Internet Message Access Protocol From Wikipedia, the free encyclopedia "IMAP" redirects here. For the antipsychotic, see Fluspirilene. Internet message access protocol (IMAP) is one of the two most prevalent Internet standard protocols for e- mail retrieval, the other being the Post Office Protocol (POP).[1] Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server.

 [edit]E-mail protocols The Internet Message Access Protocol (commonly known as IMAP) is an Application Layer Internet protocol that allows an e-mail client to access e-mail on a remote mail server. The current version, IMAP version 4 revision 1 (IMAP4rev1), is defined by RFC 3501. An IMAP server typically listens on well-known port 143. IMAP over SSL (IMAPS) is assigned well-known port number 993. IMAP supports both on-line and off-line modes of operation. E-mail clients using IMAP generally leave messages on the server until the user explicitly deletes them. This and other characteristics of IMAP operation allow multiple clients to manage the same mailbox. Most e-mail clients support IMAP in addition to POP to retrieve messages; however, fewer email services support IMAP.[2]IMAP offers access to the mail storage. Clients may store local copies of the messages, but these are considered to be a temporary cache. Incoming e-mail messages are sent to an e-mail server that stores messages in the recipient's email box. The user retrieves the messages with an e-mail client that uses one of a number of e-mail retrieval protocols. Some clients and servers preferentially use vendor-specific, proprietary protocols, but most support the Internet standard protocols, SMTP for sending e-mail and POP and IMAP for retrieving e-mail, allowing interoperability with other servers and clients. For example, Microsoft's Outlook client uses a proprietary protocol to communicate with a Microsoft Exchange Server server as does IBM's Notes client when communicating with a Domino server, but all of these products also support POP, IMAP, and outgoing SMTP. Support for the Internet standard protocols allows many e- mail clients such as Pegasus Mail or Mozilla Thunderbird (see comparison of e-mail clients) to access these servers, and allows the clients to be used with other servers (see list of mail servers). [edit]History IMAP was designed by Mark Crispin in 1986 as a remote mailbox protocol, in contrast to the widely used POP, a protocol for retrieving the contents of a mailbox.[3] IMAP was previously known as Internet Mail Access Protocol, Interactive Mail Access Protocol (RFC 1064), and Interim Mail Access Protocol.[4] [edit]Original IMAP The original Interim Mail Access Protocol was implemented as a Xerox Lisp machine client and a TOPS- 20 server. No copies of the original interim protocol specification or its software exist.[citation needed] Although some of its commands and responses were similar to IMAP2, the interim protocol lacked command/response tagging and thus its syntax was incompatible with all other versions of IMAP. [edit]IMAP2 The interim protocol was quickly replaced by the Interactive Mail Access Protocol (IMAP2), defined in RFC 1064 (in 1988) and later updated by RFC 1176 (in 1990). IMAP2 introduced command/response tagging and was the first publicly distributed version. [edit]IMAP3 IMAP3 is an extinct and extremely rare variant of IMAP.[5] It was published as RFC 1203 in 1991. It was written specifically as a counter proposal to RFC 1176, which itself proposed modifications to IMAP2.[6] IMAP3 was never accepted by the marketplace.[7][8] The IESG reclassified RFC1203 "Interactive Mail Access Protocol - Version 3" as a Historic protocol in 1993. The IMAP Working Group used RFC1176 (IMAP2) rather than RFC1203 (IMAP3) as its starting point.[9][10] [edit]IMAP2bis With the advent of MIME, IMAP2 was extended to support MIME body structures and add mailbox management functionality (create, delete, rename, message upload) that was absent in IMAP2. This experimental revision was called IMAP2bis; its specification was never published in non-draft form. An internet draft of IMAP2bis was published by the IETF IMAP Working Group in October 1993. This draft was based upon the following earlier specifications: unpublished IMAP2bis.TXT document, RFC1176, and RFC1064 (IMAP2).[11] The IMAP2bis.TXT draft documented the state of extensions to IMAP2 as of December 1992.[12] Early versions of Pine were widely distributed with IMAP2bis support[5] (Pine 4.00 and later supports IMAP4rev1). [edit]IMAP4 An IMAP Working Group formed in the IETF in the early 1990s took over responsibility for the IMAP2bis design. The IMAP WG decided to rename IMAP2bis to IMAP4 to avoid confusion with a competing IMAP3 proposal from another group that never got off the ground.[citation needed] The expansion of the IMAP acronym also changed to the Internet Message Access Protocol [edit]Advantages over POP [edit]Connected and disconnected modes of operation When using POP, clients typically connect to the e-mail server briefly, only as long as it takes to download new messages. When using IMAP4, clients often stay connected as long as the user interface is active and download message content on demand. For users with many or large messages, this IMAP4 usage pattern can result in faster response times. [edit]Multiple clients simultaneously connected to the same mailbox The POP protocol requires the currently connected client to be the only client connected to the mailbox. In contrast, the IMAP protocol specifically allows simultaneous access by multiple clients and provides mechanisms for clients to detect changes made to the mailbox by other, concurrently connected, clients. See for example RFC3501 section 5.2 which specifically cites "simultaneous access to the same mailbox by multiple agents" as an example. [edit]Access to MIME message parts and partial fetch Usually all Internet e-mail is transmitted in MIME format, allowing messages to have a tree structure where the leaf nodes are any of a variety of single part content types and the non-leaf nodes are any of a variety of multipart types. The IMAP4 protocol allows clients to separately retrieve any of the individual MIME parts and also to retrieve portions of either individual parts or the entire message. These mechanisms allow clients to retrieve the text portion of a message without retrieving attached files or to stream content as it is being fetched. [edit]Message state information Through the use of flags defined in the IMAP4 protocol, clients can keep track of message state; for example, whether or not the message has been read, replied to, or deleted. These flags are stored on the server, so different clients accessing the same mailbox at different times can detect state changes made by other clients. POP provides no mechanism for clients to store such state information on the server so if a single user accesses a mailbox with two different POP clients, state information—such as whether a message has been accessed—cannot be synchronized between the clients. The IMAP4 protocol supports both pre-defined system flags and client defined keywords. System flags indicate state information such as whether a message has been read. Keywords, which are not supported by all IMAP servers, allow messages to be given one or more tags whose meaning is up to the client. Adding user created tags to messages is an operation supported by some web-based email services, such as Gmail. [edit]Multiple mailboxes on the server IMAP4 clients can create, rename, and/or delete mailboxes (usually presented to the user as folders) on the server, and move messages between mailboxes. Multiple mailbox support also allows servers to provide access to shared and public folders. The IMAP4 Access Control List (ACL) Extension (RFC 4314) may be used to regulate access rights. [edit]Server-side searches IMAP4 provides a mechanism for a client to ask the server to search for messages meeting a variety of criteria. This mechanism avoids requiring clients to download every message in the mailbox in order to perform these searches. [edit]Built-in extension mechanism Reflecting the experience of earlier Internet protocols, IMAP4 defines an explicit mechanism by which it may be extended. Many extensions to the base protocol have been proposed and are in common use. IMAP2bis did not have an extension mechanism, and POP now has one defined by RFC 2449. [edit]Disadvantages While IMAP remedies many of the shortcomings of POP, this inherently introduces additional complexity. Much of this complexity (e.g., multiple clients accessing the same mailbox at the same time) is compensated for by server- side workarounds such as Maildir or database backends. The IMAP specification has been criticised for being insufficiently strict and allowing behaviours that effectively negate its usefulness. For instance, the specification states that each message stored on the server has a "unique id" to allow the clients to identify the messages they have already seen between sessions. However, the specification also allows these UIDs to be invalidated with no restrictions, practically defeating their purpose.[13] Unless the mail storage and searching algorithms on the server are carefully implemented, a client can potentially consume large amounts of server resources when searching massive mailboxes. IMAP4 clients need to maintain a TCP/IP connection to the IMAP server in order to be notified of the arrival of new mail. Notification of mail arrival is done through in-band signaling, which contributes to the complexity of client-side IMAP protocol handling somewhat.[14] A private proposal, push IMAP, would extend IMAP to implement push e-mail by sending the entire message instead of just a notification. However, push IMAP has not been generally accepted and current IETF work has addressed the problem in other ways (see the Lemonade Profile for more information). Unlike some proprietary protocols which combine sending and retrieval operations, sending a message and saving a copy in a server-side folder with a base-level IMAP client requires transmitting the message content twice, once to SMTP for delivery and a second time to IMAP to store in a sent mail folder. This is remedied by a set of extensions defined by the IETF LEMONADE Working Group for mobile devices: URLAUTH (RFC 4467) and CATENATE (RFC 4469) in IMAP and BURL (RFC 4468) in SMTP- SUBMISSION. POP servers don't support server-side folders so clients have no choice but to store sent items on the client. Many IMAP clients can be configured to store sent mail in a client-side folder, or to BCC oneself and then filter the incoming mail instead of saving a copy in a folder directly. In addition to the LEMONADE "trio", Courier Mail Server offers a non-standard method of sending using IMAP by copying an outgoing message to a dedicated outbox folder. Like POP, IMAP is an e-mail only protocol. As a result, items such as contacts, appointments or tasks cannot be managed or accessed using IMAP. [edit]See also

. List of mail servers . Comparison of e-mail clients . Post Office Protocol (POP) . Push-IMAP . Simple Mail Access Protocol . Webmail . IMAP IDLE

MIME From Wikipedia, the free encyclopedia This article is about the email content type system. For the World Wide Web content type system, see Internet media type. For mime as an art form, see Mime artist. For the British engineering society, see Institution of Mechanical Engineers. Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email to support:

. Text in character sets other than ASCII . Non-text attachments . Message bodies with multiple parts . Header information in non-ASCII character sets MIME's use, however, has grown beyond describing the content of email to describe content type in general, including for the web (see Internet media type) and as a storage for rich content in some commercial products (e.g., IBM Lotus Domino and IBM Lotus Quickr). Virtually all human-written Internet email and a fairly large proportion of automated email is transmitted via SMTP in MIME format. Internet email is so closely associated with the SMTP and MIME standards that it is sometimes called SMTP/MIME email.[1] The content types defined by MIME standards are also of importance outside of email, such as in communication protocols like HTTP for the World Wide Web. HTTP requires that data be transmitted in the context of email- like messages, although the data most often is not actually email. MIME is specified in six linked RFC memoranda: RFC 2045, RFC 2046, RFC 2047, RFC 4288, RFC 4289 and RFC 2049, which together define the specifications. [edit]Introduction The basic Internet email transmission protocol, SMTP, supports only 7-bit ASCII characters (see also 8BITMIME). This effectively limits Internet email to messages which, when transmitted, include only the characters sufficient for writing a small number of languages, primarily English. Other languages based on the Latin alphabet typically include diacritics and are not supported in 7-bit ASCII, meaning text in these languages cannot be correctly represented in basic email. MIME defines mechanisms for sending other kinds of information in email. These include text in languages other than English using character encodings other than ASCII, and 8-bit binary content such as files containing images, sounds, movies, and computer programs. Parts of MIME are also reused in communication protocols such as HTTP, which requires that data be transmitted in the context of email-like messages even though the data might not (and usually doesn't) actually have anything to do with email, and the message body can actually be binary. Mapping messages into and out of MIME format is typically done automatically by an email client or by mail servers when sending or receiving Internet (SMTP/MIME) email. The basic format of Internet email is defined in RFC 5322, which is an updated version of RFC 2822 and RFC 822. These standards specify the familiar formats for text email headers and body and rules pertaining to commonly used header fields such as "To:", "Subject:", "From:", and "Date:". MIME defines a collection of email headers for specifying additional attributes of a message including content type, and defines a set of transfer encodings which can be used to represent 8-bit binary data using characters from the 7-bit ASCII character set. MIME also specifies rules for encoding non-ASCII characters in email message headers, such as "Subject:", allowing these header fields to contain non-English characters. MIME is extensible. Its definition includes a method to register new content types and other MIME attribute values. The goals of the MIME definition included requiring no changes to existing email servers and allowing plain text email to function in both directions with existing clients. These goals were achieved by using additional RFC 822- style headers for all MIME message attributes and by making the MIME headers optional with default values ensuring a non-MIME message is interpreted correctly by a MIME-capable client. A simple MIME text message is therefore likely to be interpreted correctly by a non-MIME client even if it has email headers which the non-MIME client won't know how to interpret. Similarly, if the quoted printable transfer encoding (see below) is used, the ASCII part of the message will be intelligible to users with non- MIME clients. [edit]MIME headers [edit]MIME-Version The presence of this header indicates the message is MIME-formatted. The value is typically "1.0" so this header appears as

MIME-Version: 1.0

According to MIME co-creator Nathaniel Borenstein, the intention was to allow MIME to change, to advance to version 2.0 and so forth, but this decision led to the opposite outcome, making it nearly impossible to create a new version of the standard. "We did not adequately specify how to handle a future MIME version," Borenstein said. "So if you write something that knows 1.0, what should you do if you encounter 2.0 or 1.1? I sort of thought it was obvious but it turned out everyone implemented that in different ways. And the result is that it would be just about impossible for the Internet to ever define a 2.0 or a 1.1."[2] [edit]Content-ID The Content-ID header is primarily of use in multi-part messages (as discussed below); a Content-ID is a permanently globally unique identifier for a message part, allowing each part to be universally referred to by its Content-ID (e.g., in IMG tags of an HTML message allowing the inline display of attached images).[3] The content ID is contained within angle brackets in the Content-ID header. Here is an example:

Content-ID: <[email protected] >

The standards don't really have a lot to say about exactly what is in a Content-ID; they're only supposed to be globally and permanently unique (meaning that no two are ever the same, even when generated by different people in different times and places). To achieve this, some conventions have been adopted; one of them is to include an at sign (@), with the hostname of the computer which created the content ID to the right of it. This ensures the content ID is different from any created by other computers (well, at least it is when the originating computer has a unique Internet hostname; if, as sometimes happens, an anonymous machine inserts something generic like localhost, uniqueness is no longer guaranteed). Then, the part to the left of the at sign is designed to be unique within that machine; a good way to do this is to append several constantly-changing strings that programs have access to. In this case, four different numbers were inserted, with dots between them: the rightmost one is a timestamp of the number of seconds since January 1, 1970, known as the Unix epoch; to the left of it is the process ID of the program that generated the message (on servers running Unix or Linux, each process has a number which is unique among the processes in progress at any moment, though they do repeat over time); to the left of that is a count of the number of messages generated so far by the current process; and the leftmost number is the number of parts in the current message that have been generated so far. Put together, these guarantee that the content ID will never repeat; even if multiple messages are generated within the same second, they either have different process IDs or a different count of messages generated by the same process. That's just an example of how a unique content ID can be generated; different programs do it differently. It's only necessary that they remain unique, a requirement that is necessary to ensure that, even if a bunch of different messages are joined together as part of a bigger multi-part message (as happens when a message is forwarded as an attachment, or assembled into a MIME-format digest), you won't have two parts with the same content ID, which would be likely to confuse mail programs greatly. There's a similar header called Message-ID which assigns a unique identifier to the message as a whole; this is not actually part of the MIME standards, since it can be used on non-MIME as well as MIME messages. If the originating mail program doesn't add a message ID, a server handling the message later on probably will, since a number of programs (both clients and servers) want every message to have one to keep track of them. Some headers discussed in the Other Headers article make use of message IDs. When referenced in the form of a Web URI, content IDs and message IDs are placed within the URI schemes cid and mid respectively, without the angle brackets: cid:[email protected]. net [edit]Content-Type This header indicates the Internet media type of the message content, consisting of a type and subtype, for example

Content-Type: text/plain

Through the use of the multipart type, MIME allows messages to have parts arranged in a tree structure where the leaf nodes are any non-multipart content type and the non-leaf nodes are any of a variety of multipart types. This mechanism supports:

. simple text messages using text/plain (the default value for "Content-Type: ") . text plus attachments (multipart/mixed with a text/plain part and other non-text parts). A MIME message including an attached file generally indicates the file's original name with the "Content-disposition:" header, so the type of file is indicated both by the MIME content-type and the (usually OS-specific) filename extension . reply with original attached (multipart/mixed with a text/plain part and the original message as a message/rfc822 part) . alternative content, such as a message sent in both plain text and another format such as HTML (multipart/alternative with the same content in text/plain and text/html forms) . image, audio, video and application (for example, image/jpeg, audio/mp3, video/mp4, and application/msword and so on) . many other message constructs [edit]Content-Disposition The original MIME specifications only described the structure of mail messages. They did not address the issue of presentation styles. The content-disposition header field was added in RFC 2183 to specify the presentation style. A MIME part can have:

. an inline content-disposition, which means that it should be automatically displayed when the message is displayed, or . an attachment content-disposition, in which case it is not displayed automatically and requires some form of action from the user to open it. In addition to the presentation style, the content- disposition header also provides fields for specifying the name of the file, the creation date and modification date, which can be used by the reader's mail user agent to store the attachment. The following example is taken from RFC 2183, where the header is defined

Content-Disposition: attachment; filename=genome.jpeg; modification-date="Wed, 12 February 1997 16:29:51 -0500";

The filename may be encoded as defined by RFC 2231. As of 2010, a good majority of mail user agents do not follow this prescription fully. The widely used Mozilla Thunderbird mail client makes its own decisions about which MIME parts should be automatically displayed, ignoring the content-disposition headers in the messages. Thunderbird prior to version 3 also sends out newly composed messages with inline content-disposition for all MIME parts. Most users are unaware of how to set the content-disposition to attachment.[4] Many mail user agents also send messages with the file name in the name parameter of the content-type header instead of the filename parameter of the content- disposition header. This practice is discouraged.[5] [edit]Content-Transfer-Encoding In June 1992, MIME (RFC 1341, since made obsolete by RFC 2045) defined a set of methods for representing binary data in ASCII text format. The content-transfer- encoding: MIME header has 2-sided significance:

. It indicates whether or not a binary-to-text encoding scheme has been used on top of the original encoding as specified within the Content-Type header: 1. If such a binary-to-text encoding method has been used, it states which one. 2. If not, it provides a descriptive label for the format of content, with respect to the presence of 8 bit or binary content. The RFC and the IANA's list of transfer encodings define the values shown below, which are not case sensitive. Note that '7bit', '8bit', and 'binary' mean that no binary-to- text encoding on top of the original encoding was used. In these cases, the header is actually redundant for the email client to decode the message body, but it may still be useful as an indicator of what type of object is being sent. Values 'quoted-printable' and 'base64' tell the email client that a binary-to-text encoding scheme was used and that appropriate initial decoding is necessary before the message can be read with its original encoding (e.g. UTF- 8).

. Suitable for use with normal SMTP: . 7bit – up to 998 octets per line of the code range 1..127 with CR and LF (codes 13 and 10 respectively) only allowed to appear as part of a CRLF line ending. This is the default value. . quoted-printable – used to encode arbitrary octet sequences into a form that satisfies the rules of 7bit. Designed to be efficient and mostly human readable when used for text data consisting primarily of US- ASCII characters but also containing a small proportion of bytes with values outside that range. . base64 – used to encode arbitrary octet sequences into a form that satisfies the rules of 7bit. Designed to be efficient for non-text 8 bit and binary data. Sometimes used for text data that frequently uses non-US-ASCII characters. . Suitable for use with SMTP servers that support the 8BITMIME SMTP extension: . 8bit – up to 998 octets per line with CR and LF (codes 13 and 10 respectively) only allowed to appear as part of a CRLF line ending. . Suitable only for use with SMTP servers that support the BINARYMIME SMTP extension (RFC 3030): . binary – any sequence of octets. There is no encoding defined which is explicitly designed for sending arbitrary binary data through SMTP transports with the 8BITMIME extension. Thus base64 or quoted- printable (with their associated inefficiency) must sometimes still be used. This restriction does not apply to other uses of MIME such as Web Services with MIME attachments or MTOM [edit]Encoded-Word Since RFC 2822, conforming message header names and values should be ASCII characters; values that contain non-ASCII data should use the MIME encoded- word syntax (RFC 2047) instead of a literal string. This syntax uses a string of ASCII characters indicating both the original character encoding (the "charset") and the content-transfer-encoding used to map the bytes of the charset into ASCII characters. The form is: "=?charset?encoding?encoded text?=". . charset may be any character set registered with IANA. Typically it would be the same charset as the message body. . encoding can be either "Q" denoting Q-encoding that is similar to the quoted-printable encoding, or "B" denoting base64 encoding. . encoded text is the Q-encoded or base64-encoded text. . An encoded-word may not be more than 75 characters long, including charset, encoding, encoded text, and delimiters. If it is desirable to encode more text than will fit in an encoded-word of 75 characters, multiple encoded-words (separated by CRLF SPACE) may be used. [edit]Difference between Q-encoding and quoted- printable The ASCII codes for the question mark ("?") and equals sign ("=") may not be represented directly as they are used to delimit the encoded-word. The ASCII code for space may not be represented directly because it could cause older parsers to split up the encoded word undesirably. To make the encoding smaller and easier to read the underscore is used to represent the ASCII code for space creating the side effect that underscore cannot be represented directly. Use of encoded words in certain parts of headers imposes further restrictions on which characters may be represented directly. For example, Subject: =?iso-8859-1?Q?=A1Hola,_se=F1or!?= is interpreted as "Subject: ¡Hola, señor!". The encoded-word format is not used for the names of the headers (for example Subject). These header names are always in English in the raw message. When viewing a message with a non-English email client, the header names are usually translated by the client. [edit]Multipart messages A MIME multipart message contains a boundary in the "Content-Type: " header; this boundary, which must not occur in any of the parts, is placed between the parts, and at the beginning and end of the body of the message, as follows:

MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=frontier

This is a message with multiple parts in MIME format. --frontier Content-Type: text/plain

This is the body of the message. --frontier Content-Type: application/octet-stream Content-Transfer-Encoding: base64

PGh0bWw+CiAgPGhlYWQ+CiAgPC9oZWFkPgogIDxib2R 5PgogICAgPHA+VGhpcyBpcyB0aGUg Ym9keSBvZiB0aGUgbWVzc2FnZS48L3A+CiAgPC9ib2R 5Pgo8L2h0bWw+Cg= --frontier--

Each part consists of its own content header (zero or more Content- header fields) and a body. Multipart content can be nested. The content-transfer-encoding of a multipart type must always be "7bit", "8bit" or "binary" to avoid the complications that would be posed by multiple levels of decoding. The multipart block as a whole does not have a charset; non-ASCII characters in the part headers are handled by the Encoded-Word system, and the part bodies can have charsets specified if appropriate for their content-type. Notes:

. Before the first boundary is an area that is ignored by MIME-compliant clients. This area is generally used to put a message to users of old non-MIME clients. . It is up to the sending mail client to choose a boundary string that doesn't clash with the body text. Typically this is done by inserting a long random string. . The last boundary must have two hyphens at the end. [edit]Multipart subtypes The MIME standard defines various multipart-message subtypes, which specify the nature of the message parts and their relationship to one another. The subtype is specified in the "Content-Type" header of the overall message. For example, a multipart MIME message using the digest subtype would have its Content-Type set as "multipart/digest". The RFC initially defined 4 subtypes: mixed, digest, alternative and parallel. A minimally compliant application must support mixed and digest; other subtypes are optional. Applications must treat unrecognised subtypes as "multipart/mixed". Additional subtypes, such as signed and form-data, have since been separately defined in other RFCs. The following is a list of the most commonly used subtypes; it is not intended to be a comprehensive list. [edit]Mixed Multipart/mixed is used for sending files with different "Content-Type" headers inline (or as attachments). If sending pictures or other easily readable files, most mail clients will display them inline (unless otherwise specified with the "Content-disposition" header). Otherwise it will offer them as attachments. The default content-type for each part is "text/plain". Defined in RFC 2046, Section 5.1.3 [edit]Digest Multipart/digest is a simple way to send multiple text messages. The default content-type for each part is "message/rfc822". Defined in RFC 2046, Section 5.1.5 [edit]Message A message/rfc822 part contains an email message, including any headers. Rfc822 is a misnomer, since the message may be a full MIME message. This is used for digests as well as for email forwarding. Defined in RFC 2046. [edit]Alternative The multipart/alternative subtype indicates that each part is an "alternative" version of the same (or similar) content, each in a different format denoted by its "Content-Type" header. The formats are ordered by how faithful they are to the original, with the least faithful first and the most faithful last. Systems can then choose the "best" representation they are capable of processing; in general, this will be the last part that the system can understand, although other factors may affect this. Since a client is unlikely to want to send a version that is less faithful than the plain text version, this structure places the plain text version (if present) first. This makes life easier for users of clients that do not understand multipart messages. Most commonly, multipart/alternative is used for email with two parts, one plain text (text/plain) and one HTML (text/html). The plain text part provides backwards compatibility while the HTML part allows use of formatting and hyperlinks. Most email clients offer a user option to prefer plain text over HTML; this is an example of how local factors may affect how an application chooses which "best" part of the message to display. While it is intended that each part of the message represent the same content, the standard does not require this to be enforced in any way. At one time, anti-spam filters would only examine the text/plain part of a message,[citation needed] because it is easier to parse than the text/html part. But spammers eventually took advantage of this, creating messages with an innocuous-looking text/plain part and advertising in the text/html part. Anti- spam software eventually caught up on this trick, penalizing messages with very different text in a multipart/alternative message.[citation needed] Defined in RFC 2046, Section 5.1.4 [edit]Related A multipart/related is used to indicate that each message part is a component of an aggregate whole. It is for compound objects consisting of several inter-related components - proper display cannot be achieved by individually displaying the constituent parts. The message consists of a root part (by default, the first) which reference other parts inline, which may in turn reference other parts. Message parts are commonly referenced by the "Content-ID" part header. The syntax of a reference is unspecified and is instead dictated by the encoding or protocol used in the part. One common usage of this subtype is to send a web page complete with images in a single message. The root part would contain the HTML document, and use image tags to reference images stored in the latter parts. Defined in RFC 2387 [edit]Report Multipart/report is a message type that contains data formatted for a mail server to read. It is split between a text/plain (or some other content/type easily readable) and a message/delivery-status, which contains the data formatted for the mail server to read. Defined in RFC 6522 [edit]Signed A multipart/signed message is used to attach a digital signature to a message. It has two parts, a body part and a signature part. The whole of the body part, including mime headers, is used to create the signature part. Many signature types are possible, like application/pgp-signature (RFC 3156) and application/pkcs7-signature (S/MIME). Defined in RFC 1847, Section 2.1 [edit]Encrypted A multipart/encrypted message has two parts. The first part has control information that is needed to decrypt the application/octet-stream second part. Similar to signed messages, there are different implementations which are identified by their separate content types for the control part. The most common types are "application/pgp- encrypted" (RFC 3156) and "application/pkcs7-mime" (S/MIME). Defined in RFC 1847, Section 2.2 [edit]Form Data As its name implies, multipart/form-data is used to express values submitted through a form. Originally defined as part of HTML 4.0, it is most commonly used for submitting files via HTTP. Defined in RFC 2388 [edit]Mixed-Replace (experimental) The content type multipart/x-mixed-replace was developed as part of a technology to emulate server push and streaming over HTTP. All parts of a mixed-replace message have the same semantic meaning. However, each part invalidates - "replaces" - the previous parts as soon as it is received completely. Clients should process the individual parts as soon as they arrive and should not wait for the whole message to finish. Originally developed by Netscape,[6] it is still supported by Mozilla, Firefox, Chrome,[7] Safari (but not in Safari on the iPhone)[citation needed] and Opera, but traditionally ignored by Microsoft. It is commonly used in IP cameras as the MIME type for MJPEG streams.[8] [edit]Byteranges The multipart/byteranges is used to represent noncontiguous byte ranges of a single message. It is used by HTTP when a server returns multiple byte ranges and is defin

100BASE-T  Reprints In 100 Mbps (megabits per second) Ethernet (known as Fast Ethernet), there are three types of physical wiring that can carry signals:

 100BASE-T4 (four pairs of telephone twisted pair wire)  100BASE-TX (two pairs of data grade twisted-pair wire)  100BASE-FX (a two-strand optical fiber cable) This designation is an Institute of Electrical and Electronics Engineers shorthand identifier. The "100" in the media type designation refers to the transmission speed of 100 Mbps. The "BASE" refers to baseband signalling, which means that only Ethernet signals are carried on the medium. The "T4," "TX," and "FX" refer to the physical medium that carries the signal. (Through repeaters, media segments of different physical types can be used in the same system.)

The TX and FX types together are sometimes referred to as "100BASE-X." (The designation for "100BASE-T" is also sometimes seen as "100BaseT.")

RELATED GLOSSARY TERMS: MDI/MDIX (medium dependent interface/MDI crossover), 802.3,Ethernet Glossary, Quad FastEthernet (QFE), 10BASE-2, coaxial cable (illustrated), Power over Ethernet (PoE), Ethernet point-of-presence (EPOP), DVMRP (Distance Vector Multicast Routing Protocol), 1000BASE-T 100Base-T

An Ethernet standard that transmits at 100 Mbps. Called "Fast Ethernet" when first deployed in 1995 and officially the IEEE 802.3u standard, it is a 100 Mbps version of 10Base-T (10 Mbps Ethernet). Like 10Base-T, 100Base-T is a shared media LAN when used with a hub (all nodes share the 100 Mbps) and 100 Mbps between each pair of nodes when used with a switch. Most Ethernet adapters and switches are 10/100 devices, which support both 100Base-T and 10Base-T (see 10/100 adapter).

100Base-T, 100Base-T4 and 100Base-TX 100Base-T uses two pairs of wires in Category 5 UTP cable, while 100Base-TX requires two pairs in Category 6 cable. 100Base-T4 uses all four wire pairs in older Category 3 cables. See 10Base- T and 100Base-FX.

"Twisted Pair" Ethernet All stations in a 10Base-T and 100Base-T Ethernet are wired to a central hub or switch using twisted pair wires and RJ-45 connectors.

Post Office Protocol From Wikipedia, the free encyclopedia This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2007) In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection.[1] POP and IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-mail retrieval.[2] Virtually all modern e-mail clients and servers support both. The POP protocol has been developed through several versions, with version 3 (POP3) being the current standard. Most webmail service providers such as Hotmail, Gmail and Yahoo! Mail also provide IMAP and POP3 service. [edit]Overview POP supports simple download-and-delete requirements for access to remote mailboxes (termed maildrop in the POP RFC's).[3] Although most POP clients have an option to leave mail on server after download, e-mail clients using POP generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect. Other protocols, notably IMAP, (Internet Message Access Protocol) provide more complete and complex remote access to typical mailbox operations. Many e-mail clients support POP as well as IMAP to retrieve messages; however, fewer Internet Service Providers (ISPs) support IMAP[citation needed]. A POP3 server listens on well-known port 110. Encrypted communication for POP3 is either requested after protocol initiation, using the STLS command, if supported, or by POP3S, which connects to the server using Transport Layer Security (TLS) or Secure Sockets Layer (SSL) on well- known TCP port 995. Available messages to the client are fixed when a POP session opens the maildrop, and are identified by message-number local to that session or, optionally, by a unique identifier assigned to the message by the POP server. This unique identifier is permanent and unique to the maildrop and allows a client to access the same message in different POP sessions. Mail is retrieved and marked for deletion by message-number. When the client exits the session, the mail marked for deletion is removed from the maildrop. [edit]History POP (POP1) is specified in RFC 918 (1984), POP2 by RFC 937 (1985). The original specification of POP3 is RFC 1081 (1988). Its current specification is RFC 1939, updated with an extension mechanism, RFC 2449 and an authentication mechanism in RFC 1734. POP2 has been assigned well-known port 109. The original POP3 specification supported only an unencrypted USER/PASS login mechanism or Berkeley .rhosts access control. POP3 currently supports several authentication methods to provide varying levels of protection against illegitimate access to a user's e-mail. Most are provided by the POP3 extension mechanisms. POP3 clients support SASL authentication methods via the AUTH extension. MIT Project Athena also produced a Kerberized version. RFC 1460 introduced APOP into the core protocol. APOP is a challenge/response protocol which uses the MD5 hash function in an attempt to avoid replay attacks and disclosure of the shared secret. Clients implementing APOP include Mozilla Thunderbird, Opera Mail, Eudora, KMail, Novell Evolution, RimArts' Becky!,[4] Windows Live Mail, PowerMail, Apple Mail, and Mutt. An informal proposal had been outlined for a "POP4" specification, complete with a working server implementation. This "POP4" proposal added basic folder management, multipart message support, as well as message flag management, allowing for a light protocol which supports some popular IMAP features which POP3 currently lacks. However, in doing so, it shared with IMAP the embedding in a communication protocol a specific model of a mailbox, which, although common, is not universal. No progress has been observed in this "POP4" proposal since 2003.[5] [edit]Extensions An extension mechanism was proposed in RFC 2449 to accommodate general extensions as well as announce in an organized manner support for optional commands, such as TOP and UIDL. The RFC did not intend to encourage extensions, and reaffirmed that the role of POP3 is to provide simple support for mainly download- and-delete requirements of mailbox handling. The extensions are termed capabilities and are listed by the CAPA command. Except for APOP, the optional commands were included in the initial set of capabilities. Following the lead of ESMTP (RFC 5321), capabilities beginning with an X signify local capabilities. [edit]STARTTLS The STARTTLS extension allows the use of Transport Layer Security (TLS) or Secure Sockets Layer (SSL) to be negotiated using the STLS command, on the standard POP3 port, rather than an alternate. Some clients and servers instead use the alternate-port method, which uses TCP port 995 (POP3S). [edit]SDPS Demon Internet introduced extensions to POP3 that allow multiple accounts per domain, and has become known as Standard Dial-up POP3 Service (SDPS).[1] To access each account, the username includes the hostname, as john@hostname or john+hostname. Google Apps uses the same method. [edit]Comparison with IMAP Clients that leave mail on servers generally use the UIDL command to get the current association of message- numbers to message identified by its unique identifier. The unique identifier is arbitrary, and might be repeated if the mailbox contains identical messages. In contrast, IMAP uses a 32-bit unique identifier (UID) that is assigned to messages in ascending (although not necessarily consecutive) order as they are received. When retrieving new messages, an IMAP client requests the UIDs greater than the highest UID among all previously-retrieved messages, whereas a POP client must fetch the entire UIDL map. For large mailboxes, this can require significant processing. MIME serves as the standard for attachments and non- ASCII text in e-mail. Although neither POP3 nor SMTP require MIME-formatted e-mail, essentially all non-ASCII Internet e-mail comes MIME-formatted, so POP clients must also understand and use MIME. IMAP, by design, assumes MIME-formatted e-mail.

IPv6 From Wikipedia, the free encyclopedia IPv6 (Internet Protocol version 6) is a version of the Internet Protocol (IP) that is intended to succeed IPv4, which is the communications protocolcurrently used to direct almost all Internet traffic.[1] IPv6 will allow the Internet to support many more devices by greatly increasing the number of possible addresses.

Logo for IPv6 released by the Internet Society. The Internet operates by transferring data between hosts in packets that are routed across networks as specified by routing protocols. These packets require an addressing scheme, such as IPv4 or IPv6, to specify their source and destination. Each host, computer or other device on the Internet must be assigned an IP address in order to communicate. The growth of the Internet has created a need for more addresses than are possible with IPv4, which allows 32 bits for an IP address, and therefore has 232 (4 294 967 296) possible addresses. IPv6, which was developed by the Internet Engineering Task Force (IETF) to deal with this long-anticipated IPv4 address exhaustion, uses 128-bit addresses, allowing 2128 (approximately3.4×1038) addresses. This expansion can accommodate vastly more devices and users on the internet as well as providing greater flexibility in allocating addresses and efficiency for routing traffic. It also eliminates the primary need for network address translation (NAT), which has gained widespread deployment as an effort to alleviate IPv4 address exhaustion. Like IPv4, IPv6 is an internet-layer protocol for packet- switched internetworking and provides end-to- end datagram transmission across multiple IP networks. It is described in Internet standard document RFC 2460, published in December 1998.[2] In addition to offering more addresses, IPv6 also implements features not present in IPv4. It simplifies aspects of address assignment (stateless address autoconfiguration), network renumbering and router announcements when changing network connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link- layer media addressing information (MAC address). Network security is also integrated into the design of the IPv6 architecture, including the option of IPsec. The last top level (/8) blocks of 16 million free IPv4 addresses were assigned in February 2011 by the Internet Assigned Numbers Authority (IANA) to the five Regional Internet registries (RIRs). However, many free addresses still remain within most assigned blocks, and each RIR will continue with standard address allocation policy until it is at its last /8 block. After that, only blocks of 1024 addresses (a /22) will be made available from the RIR to each Local Internet registry (LIR). As of February 2011, only the Asia-Pacific Network Information Centre (APNIC) had reached this stage.[3] For the Internet to make use of the advantages of IPv6 over IPv4, most hosts on the Internet, as well as the networks connecting them, need to deploy the IPv6 protocol. However, IPv6 deployment has been slow. While deployment of IPv6 is accelerating, especially in the Asia- Pacific region and some European countries, areas such as the Americas and Africa are comparatively lagging in deployment of IPv6. IPv6 does not implement interoperability features with IPv4, and creates essentially a parallel, independent network. Exchanging traffic between the two networks requires special translator gateways, but modern computer operating systems implement dual-protocol software for transparent access to both networks either natively or using atunneling protocol such as 6to4, 6in4, or Teredo. In December 2010, despite marking its 12th anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general worldwide deployment. [edit]Motivation and origin [edit]IPv4 Main article: IPv4

Decomposition of an IPv4 address to its binary value. Internet Protocol Version 4 (IPv4) was the first publicly used version of the Internet Protocol. IPv4 addresses are typically displayed as four numbers, each in the range 0 to 255, or 8 bits per number, for a total of 32 bits. Thus IPv4 provides an addressing capability of 232 or approximately 4.3 billion addresses. Address exhaustion was not initially a concern in IPv4 as this version was originally presumed to be an internal test within ARPA, and not intended for public use. The decision to put a 32-bit address space on there was the result of a year's battle among a bunch of engineers who couldn't make up their minds about 32, 128, or variable-length. And after a year of fighting, I said—I'm now at ARPA, I'm running the program, I'm paying for this stuff, I'm using American tax dollars, and I wanted some progress because we didn't know if this was going to work. So I said: OK, it's 32-bits. That's enough for an experiment; it's 4.3 billion terminations. Even the Defense Department doesn't need 4.3 billion of everything and couldn't afford to buy 4.3 billion edge devices to do a test anyway. So at the time I thought we were doing an experiment to prove the technology and that if it worked we'd have opportunity to do a production version of it. Well, it just escaped! It got out and people started to use it, and then it became a commercial thing. So this [IPv6] is the production attempt at making the network scalable. —Vint Cerf, Google IPv6 Conference 2008[4] During the first decade of operation of the Internet (by the late 1980s), it became apparent that methods had to be developed to conserve address space. In the early 1990s, even after the redesign of the addressing system using a classless network model, it became clear that this would not suffice to prevent IPv4 address exhaustion, and that further changes to the Internet infrastructure were needed.[5] [edit]Working-group proposal By the beginning of 1992, several proposals appeared and by the end of 1992, the IETF announced a call for white papers.[6] In September 1993, the IETF created a temporary, ad-hoc IP Next Generation (IPng) area to deal specifically with IPng issues. The new area was led by Allison Mankin and Scott Bradner, and had a directorate with 15 engineers from diverse backgrounds for direction- setting and preliminary document review:[5][7] The working- group members were J. Allard (Microsoft), Steve Bellovin (AT&T), Jim Bound (Digital Equipment Corporation), Ross Callon (Wellfleet), Brian Carpenter (CERN), Dave Clark (MIT), John Curran (NEARNET), Steve Deering (Xerox), Dino Farinacci (Cisco), Paul Francis (NTT), Eric Fleischmann (Boeing), Mark Knopper (Ameritech), Greg Minshall (Novell), Rob Ullmann (Lotus), and Lixia Zhang (Xerox).[citation needed] The Internet Engineering Task Force adopted the IPng model on July 25, 1994, with the formation of several IPng working groups.[5] By 1996, a series of RFCs was released defining Internet Protocol version 6 (IPv6), starting with RFC 1883. (Version 5 was used by the experimental Internet Stream Protocol.) It is widely expected that the Internet will use IPv4 alongside IPv6 for the foreseeable future. IPv4-only and IPv6-only nodes cannot communicate directly, and need assistance from an intermediary gateway or must use other transition mechanisms. [edit]Exhaustion of IPv4 addresses Main article: IPv4 address exhaustion On February 3, 2011, in a ceremony in Miami, the Internet Assigned Numbers Authority (IANA) assigned the last batch of five /8 address blocks to the Regional Internet Registries,[8] officially depleting the global pool of completely fresh blocks of addresses.[9] Each /8 address block represents approximately 16.7 million possible addresses, for a total of over 80 million potential addresses combined. At the time, it was anticipated that these addresses could well be fully consumed within three to six months at then- current rates of allocation.[10] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, which will be allocated in a much more restricted way.[11] In 2003, the director of Asia-Pacific Network Information Centre (APNIC), Paul Wilson, stated that, based on then- current rates of deployment, the available space would last for one or two decades.[12] In September 2005, a report by Cisco Systems suggested that the pool of available addresses would exhaust in as little as 4 to 5 years.[13] In 2008, a policy process started for the end- game and post-exhaustion era.[14] In 2010, a daily updated report projected the global address pool exhaustion by the first quarter of 2011, and depletion at the five regional Internet registriesbefore the end of 2011.[15] [edit]Comparison to IPv4 IPv6 specifies a new packet format, designed to minimize packet header processing by routers.[2][16] Because the headers of IPv4 packets and IPv6 packets are significantly different, the two protocols are not interoperable. However, in most respects, IPv6 is a conservative extension of IPv4. Most transport and application-layer protocols need little or no change to operate over IPv6; exceptions are application protocols that embed internet- layer addresses, such as FTP and NTPv3, where the new address format may cause conflicts with existing protocol syntax. [edit]Larger address space

Decomposition of an IPv6 address into its binary form The main advantage of IPv6 over IPv4 is its larger address space. The length of an IPv6 address is 128 bits, compared to 32 bits in IPv4.[2]The address space therefore has 2128 or approximately 3.4×1038 addresses. By comparison, this amounts to approximately 4.8×1028addresses for each of the seven billion people alive in 2011.[17] In addition, the IPv4 address space is poorly allocated, with approximately 14% of all available addresses utilized.[18] While these numbers are large, it was not the intent of the designers of the IPv6 address space to assure geographical saturation with usable addresses. Rather, the longer addresses simplify allocation of addresses, enable efficientroute aggregation, and allow implementation of special addressing features. In IPv4, complex Classless Inter-Domain Routing (CIDR) methods were developed to make the best use of the small address space. The standard size of a subnet in IPv6 is 264 addresses, the square of the size of the entire IPv4 address space. Thus, actual address space utilization rates will be small in IPv6, but network management and routing efficiency is improved by the large subnet space and hierarchical route aggregation. Renumbering an existing network for a new connectivity provider with different routing prefixes is a major effort with IPv4.[19][20] With IPv6, however, changing the prefix announced by a few routers can in principle renumber an entire network, since the host identifiers (the least- significant 64 bits of an address) can be independently self-configured by a host.[21] [edit]Multicasting Multicasting, the transmission of a packet to multiple destinations in a single send operation, is part of the base specification in IPv6. In IPv4 this is an optional although commonly implemented feature.[22] IPv6 multicast addressing shares common features and protocols with IPv4 multicast, but also provides changes and improvements by eliminating the need for certain protocols. IPv6 does not implement traditional IP broadcast, i.e. the transmission of a packet to all hosts on the attached link using a special broadcast address, and therefore does not define broadcast addresses. In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group at address ff02::1, which is analogous to IPv4 multicast to address224.0.0.1. IPv6 also provides for new multicast implementations, including embedding rendezvous point addresses in an IPv6 multicast group address, which simplifies the deployment of inter-domain solutions.[23] In IPv4 it is very difficult for an organization to get even one globally routable multicast group assignment, and the implementation of inter-domain solutions is very arcane.[24] Unicast address assignments by a local Internet registry for IPv6 have at least a 64-bit routing prefix, yielding the smallest subnet size available in IPv6 (also 64 bits). With such an assignment it is possible to embed the unicast address prefix into the IPv6 multicast address format, while still providing a 32-bit block, the least significant bits of the address, or approximately 4.2 billion multicast group identifiers.[citation needed] Thus each user of an IPv6 subnet automatically has available a set of globally routable source-specific multicast groups for multicast applications.[25] [edit]Stateless address autoconfiguration (SLAAC) See also: IPv6 address IPv6 hosts can configure themselves automatically when connected to a routed IPv6 network using the Neighbor Discovery Protocol via Internet Control Message Protocol version 6 (ICMPv6) router discovery messages. When first connected to a network, a host sends a link-local router solicitation multicast request for its configuration parameters; if configured suitably, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters.[21] If IPv6 stateless address autoconfiguration is unsuitable for an application, a network may use stateful configuration with the Dynamic Host Configuration Protocol version 6 (DHCPv6) or hosts may be configured statically. Routers present a special case of requirements for address configuration, as they often are sources for autoconfiguration information, such as router and prefix advertisements. Stateless configuration for routers can be achieved with a special router renumbering protocol.[26] [edit]Mandatory network-layer security Internet Protocol Security (IPsec) was originally developed for IPv6, but found widespread deployment first in IPv4, into which it was back-engineered. Earlier, IPsec was an integral part of the base IPv6 protocol suite,[2][27] but has since been made optional.[28] [edit]Simplified processing by routers In IPv6, the packet header and the process of packet forwarding have been simplified. Although IPv6 packet headers are at least twice the size of IPv4 packet headers, packet processing by routers is generally more efficient,[2][16] thereby extending the end-to-end principle of Internet design. Specifically:

. The packet header in IPv6 is simpler than that used in IPv4, with many rarely used fields moved to separate optional header extensions. . IPv6 routers do not perform fragmentation. IPv6 hosts are required to either perform path MTU discovery, perform end-to-end fragmentation, or to send packets no larger than the IPv6 default minimum MTU size of 1280 octets. . The IPv6 header is not protected by a checksum; integrity protection is assumed to be assured by both link-layer and higher-layer (TCP, UDP, etc.) error detection. UDP/IPv4 may actually have a checksum of 0, indicating no checksum; IPv6 requires UDP to have its own checksum. Therefore, IPv6 routers do not need to recompute a checksum when header fields (such as thetime to live (TTL) or hop count) change. This improvement may have been made less necessary by the development of routers that perform checksum computation at link speed using dedicated hardware, but it is still relevant for software-based routers. . The TTL field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue. [edit]Mobility Unlike mobile IPv4, mobile IPv6 avoids triangular routing and is therefore as efficient as native IPv6. IPv6 routers may also allow entire subnets to move to a new router connection point without renumbering.[29] [edit]Options extensibility The IPv6 protocol header has a fixed size (40 octets). Options are implemented as additional extension headers after the IPv6 header, which limits their size only by the size of an entire packet. The extension header mechanism makes the protocol extensible in that it allows future services for quality of service, security, mobility, and others to be added without redesign of the basic protocol.[2] [edit]Jumbograms IPv4 limits packets to 65535 (216−1) octets of payload. An IPv6 node can optionally handle packets over this limit, referred to as jumbograms, which can be as large as 4294967295 (232−1) octets. The use of jumbograms may improve performance over high-MTU links. The use of jumbograms is indicated by the Jumbo Payload Option header.[30] [edit]Privacy Like IPv4, IPv6 supports globally unique static IP addresses, which can be used to track a single device's Internet activity. Most devices are used by a single user, so a device's activity is often assumed to be equivalent to a user's activity. This is a cause for concern to anyone who wish to keep their Internet activity secret. Activity tracking based on IP address is a potential privacy issue for all IP-enabled devices. However, device activity can be particularly simple to track when the host identifier portion of the IPv6 address is automatically generated from the network interface's MAC address. Privacy extensions for IPv6 have been defined to address these privacy concerns.[31] When privacy extensions are enabled, the operating system generates ephemeral IP addresses by concatenating a randomly generated host identifier with the assigned network prefix. These ephemeral addresses, instead of trackable static IP addresses, are used to communicate with remote hosts. The use of ephemeral addresses makes it difficult to accurately track a user's Internet activity by scanning activity streams for a single IPv6 address.[32] Privacy extensions are enabled by default in Windows, Mac OS X (since 10.7), and iOS (since version 4.3).[33] Some Linux distributions have enabled privacy extensions as well.[34] Privacy extensions do not protect the user from other forms of activity tracking, such as tracking cookies. Privacy extensions do little to protect the user from tracking if only one or two hosts are using a given network prefix, and the activity tracker is privy to this information. In this scenario, the network prefix is the unique identifier for tracking. Network prefix tracking is less of a concern if the user's ISP assigns a dynamic network prefix via DHCP.[35][36] [edit]Packet format Main article: IPv6 packet

IPv6 packet header An IPv6 packet has two parts: a header and payload. The header consists of a fixed portion with minimal functionality required for all packets and may contain optional extensions to implement special features. The fixed header occupies the first 40 octets (320 bits) of the IPv6 packet. It contains the source and destination addresses, traffic classification options, a hop counter, and a pointer for extension headers, if any. The Next Header field, present in each extension, points to the next element in the chain of extensions. The last field points to the upper-layer protocol that is carried in the packet's payload. Extension headers carry options that are used for special treatment of a packet in the network, e.g., for routing, fragmentation, and for security using theIPsec framework. Without special options, a payload must be less than 64kB. With a Jumbo Payload option (in a Hop-By- Hop Options extension header), the payload must be less than 4 GB. Unlike in IPv4, routers never fragment a packet. Hosts are expected to use Path MTU Discovery to make their packets small enough to reach the destination without needing to be fragmented. See IPv6 Packet#Fragmentation. [edit]Addressing Main article: IPv6 address Compared to IPv4, the most obvious advantage of IPv6 is its larger address space. IPv4 addresses are 32 bits long and number about 4.3×109 (4.3 billion).[37] IPv6 addresses are 128 bits long and number about 3.4×1038. IPv6's addresses are deemed enough for the foreseeable future.[38] IPv6 addresses are written in eight groups of four hexadecimal digits separated by colons, such as 2001:0db8:85a3:0000:0000:8a2e:0370:7334. IPv6 unicast addresses other than those that start with binary 000 are logically divided into two parts: a 64-bit (sub-)network prefix, and a 64-bit interface identifier.[39] For stateless address autoconfiguration (SLAAC) to work, subnets require a /64 address block, as defined in RFC 4291 section 2.5.1. Local Internet registries get assigned at least /32 blocks, which they divide among ISPs.[40] The obsolete RFC 3177 recommended the assignment of a /48 to end-consumer sites. This was replaced by RFC 6177, which "recommends giving home sites significantly more than a single /64, but does not recommend that every home site be given a /48 either". /56s are specifically considered. It remains to be seen if ISPs will honor this recommendation; for example, during initial trials, Comcast customers were given a single /64 network.[41] IPv6 addresses are classified by three types of networking methodologies: unicast addresses identify each network interface, anycast addresses identify a group of interfaces, usually at different locations of which the nearest one is automatically selected, and multicast addresses are used to deliver one packet to many interfaces. The broadcast method is not implemented in IPv6. Each IPv6 address has a scope, which specifies in which part of the network it is valid and unique. Some addresses are unique only on the local (sub-)network. Others are globally unique. Some IPv6 addresses are reserved for special purposes, such as loopback, 6to4 tunneling, and Teredo tunneling. See RFC 5156. Also, some address ranges are considered special, such as link-local addresses for use on the local link only, Unique Local addresses (ULA) as described in RFC 4193, and solicited-node multicast addresses used in the Neighbor Discovery Protocol. [edit]IPv6 in the Domain Name System Main article: IPv6 address#IPv6 addresses in the Domain Name System In the Domain Name System, hostnames are mapped to IPv6 addresses by AAAA resource records, so- called quad-A records. For reverse resolution, the IETF reserved the domain ip6.arpa, where the name space is hierarchically divided by the 1- digit hexadecimal representation of nibble units (4 bits) of the IPv6 address. This scheme is defined in RFC 3596. [edit]Address format An IPv6 address is represented by 8 groups of 16-bit hexadecimal values separated by colons (:). For example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 The hexadecimal digits are case-insensitive. An IPv6 address can be abbreviated with the following rules: 1. Omit leading zeroes in a 16-bit value. 2. Replace one or more groups of consecutive zeroes by a double colon. Below is an example of these rules:

Address fe80 : 0000 : 0000 : 0000 : 0202 : b3ff : fe1e : 8329

After Rule fe80 : 0 : 0 : 0 : 202 : b3ff : fe1e : 8329 1

After Rule fe80 : : 202 : b3ff : fe1e : 8329 2

Below are the text representations of these addresses: fe80:0000:0000:0000:0202:b3ff:fe1e:8329 fe80:0:0:0:202:b3ff:fe1e:8329 fe80::202:b3ff:fe1e:8329 Another interesting example is the loopback address:[37] 0:0:0:0:0:0:0:1 ::1 As IPv6 addresses may have more than one representation, which can lead to confusion, there is a proposed standard for representing them in text.[42] [edit]Transition mechanisms

IPv6 transition

mechanisms

Standards Track

 4in6  6in4  6over4  DS-Lite  6rd  6to4  ISATAP  NAT64 / DNS64  Teredo  SIIT Experimental

 TSP Informational  IVI  TRT Drafts

 4rd  AYIYA  dIVI Deprecated

 NAT-PT  NAPT-PT

 V

 T

 E Until IPv6 completely supplants IPv4, a number of transition mechanisms[43] are needed to enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure. People have made various proposals for this transition period:

. RFC 2185, Routing Aspects of IPv6 Transition . RFC 2766, Network Address Translation — Protocol Translation NAT-PT, obsoleted as explained in RFC 4966 Reasons to Move the Network Address Translator — Protocol Translator NAT-PT to Historic Status . RFC 3053, IPv6 Tunnel Broker . RFC 3056, 6to4. Connection of IPv6 Domains via IPv4 Clouds . RFC 3142, An IPv6-to-IPv4 Transport Relay Translator . RFC 4213, Basic Transition Mechanisms for IPv6 Hosts and Routers . RFC 4380, Teredo: Tunneling IPv6 over UDP through Network Address Translations NATs . RFC 4798, Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE) . RFC 5214, Intra-Site Automatic Tunnel Addressing Protocol ISATAP . RFC 5569, IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) . RFC 5572, IPv6 Tunnel Broker with the Tunnel Setup Protocol (TSP) . RFC 6180, Guidelines for Using IPv6 Transition Mechanisms during IPv6 Deployment . RFC 6343, Advisory Guidelines for 6to4 Deployment [edit]Dual IP stack implementation The dual-stack protocol implementation in an operating system is a fundamental IPv4-to- IPv6 transition technology. It implements IPv4 and IPv6 protocol stacks either independently or in a hybrid form. The hybrid form is commonly implemented in modern operating systems that implement IPv6. Dual-stack hosts are described in RFC 4213. Modern hybrid dual-stack implementations of IPv4 and IPv6 allow programmers to write networking code that works transparently on IPv4 or IPv6. The software may use hybridsockets designed to accept both IPv4 and IPv6 packets. When used in IPv4 communications, hybrid stacks use an IPv6 application programming interface and represent IPv4 addresses in a special address format, the IPv4-mapped IPv6 address. [edit]IPv4-mapped IPv6 addresses Hybrid dual-stack IPv6/IPv4 implementations recognize a special class of addresses, the IPv4-mapped IPv6 addresses. In these addresses, the first 80 bits are zero, the next 16 bits are one, and the remaining 32 bits are the IPv4 address. You may see these addresses with the first 96 bits written in the standard IPv6 format, and the remaining 32 bits written in the customary dot-decimal notation of IPv4. For example, ::ffff:192.0.2.128 represents the IPv4 address 192.0.2.128. A deprecated format for IPv4-compatible IPv6 addresses was ::192.0.2.128.[44] Because of the significant internal differences between IPv4 and IPv6, some of the lower- level functionality available to programmers in the IPv6 stack does not work identically with IPv4-mapped addresses. Some common IPv6 stacks do not implement the IPv4-mapped address feature, either because the IPv6 and IPv4 stacks are separate implementations (e.g., Microsoft Windows 2000, XP, and Server 2003), or because of security concerns (OpenBSD).[45] On these operating systems, a program must open a separate socket for each IP protocol it uses. On some systems, e.g., the Linux kernel, NetBSD, and FreeBSD, this feature is controlled by the socket option IPV6_V6ONLY, as specified in RFC 3493.[46] [edit]Tunneling In order to reach the IPv6 Internet, an isolated host or network must use the existing IPv4 infrastructure to carry IPv6 packets. This is done using a technique known as tunneling, which encapsulates IPv6 packets within IPv4, in effect using IPv4 as a link layer for IPv6. IP protocol 41 indicates IPv4 packets which encapsulate IPv6 datagrams. Some routers or network address translation devices may block protocol 41. To pass through these devices, you might use UDP packets to encapsulate IPv6 datagrams. Other encapsulation schemes, such as AYIYA or Generic Routing Encapsulation, are also popular. Conversely, on IPv6-only internet links, when access to IPv4 network facilities is needed, tunneling of IPv4 over IPv6 protocol occurs, using the IPv6 as a link layer for IPv4. [edit]Automatic tunneling Automatic tunneling refers to a technique where the routing infrastructure automatically determines the tunnel endpoints. Some automatic tunneling techniques are below. 6to4 is recommended by RFC 3056. It uses protocol 41 encapsulation.[47] Tunnel endpoints are determined by using a well- known IPv4 anycast address on the remote side, and embedding IPv4 address information within IPv6 addresses on the local side. 6to4 is widely deployed today. Teredo is an automatic tunneling technique that uses UDP encapsulation and can allegedly cross multiple NAT boxes.[48] IPv6, including 6to4 and Teredo tunneling, are enabled by default inWindows Vista[49] and Windows 7. Most Unix systems implement only 6to4, but Teredo can be provided by third-party software such as Miredo. ISATAP[50] treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4 address to a link-local IPv6 address. Unlike 6to4 and Teredo, which are inter- site tunnelling mechanisms, ISATAP is an intra-site mechanism, meaning that it is designed to provide IPv6 connectivity between nodes within a single organisation. [edit]Configured and automated tunneling (6in4) In configured tunneling, the tunnel endpoints are explicitly configured, either by an administrator manually or the operating system's configuration mechanisms, or by an automatic service known as a tunnel broker;[51] this is also referred to as automated tunneling. Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, well-administered networks. Automated tunneling provides a compromise between the ease of use of automatic tunneling and the deterministic behaviour of configured tunneling. Raw encapsulation of IPv6 packets using IPv4 protocol number 41 is recommended for configured tunneling; this is sometimes known as 6in4 tunneling. As with automatic tunneling, encapsulation within UDP may be used in order to cross NAT boxes and firewalls. [edit]Proxying and translation for IPv6-only hosts Main article: IPv6 transition mechanisms After the regional Internet registries have exhausted their pools of available IPv4 addresses, it is likely that hosts newly added to the Internet might only have IPv6 connectivity. For these clients to have backward-compatible connectivity to existing IPv4-only resources, suitable IPv6 transition mechanisms must be deployed. One form of address translation is the use of a dual-stack application-layer proxy server, for example a web proxy. NAT-like techniques for application-agnostic translation at the lower layers in routers and gateways have been proposed. The NAT-PT standard was dropped due to a number of criticisms,[52]however more recently the continued low adoption of IPv6 has prompted a new standardization effort under the name NAT64. [edit]Application transition RFC 4038, Application Aspects of IPv6 Transition, is an informational RFC that covers the topic of IPv4 to IPv6 application transition mechanisms. Other RFCs that pertain to IPv6 at the application level are:

. RFC 3493, Basic Socket Interface Extensions for IPv6 . RFC 3542, Advanced Sockets Application Program Interface (API) for IPv6 Similar to the OS-level WAN stack, applications can be:

. IPv4 only . IPv6 only . dual set of IPv4 and IPv6 only . hybrid IPv4 and IPv6 [edit]IPv6 readiness Compatibility with IPv6 networking is mainly a software or firmware issue. However, much of the older hardware that could in principle be upgraded is likely to be replaced instead. The American Registry for Internet Numbers (ARIN) suggested that all Internet servers be prepared to serve IPv6-only clients by January 2012.[53] Sites will only be accessible over NAT64 if they do not use IPv4 literals as well. [edit]Software Most personal computers running recent operating system versions are IPv6- ready. Most popular applications with network capabilities are ready, and most others could be easily upgraded with help from the developers. Java applications adhering to Java 1.4 (February 2002) standards work with IPv6.[54] [edit]Hardware and embedded systems Low-level equipment such as network adapters and network switches may not be affected by the change, since they transmit link-layer frames without inspecting the contents. However, networking devices that obtain IP addresses or perform routing of IP packets do need to understand IPv6. Most equipment would be IPv6 capable with a software or firmware update if the device has sufficient storage and memory space for the new IPv6 stack. However, manufacturers may be reluctant to spend on software development costs for hardware they have already sold when they are poised for new sales from IPv6-ready equipment.[citation needed] In some cases, non-compliant equipment needs to be replaced because the manufacturer no longer exists or software updates are not possible, for example, because the network stack is implemented in permanent read-only memory. The CableLabs consortium published the 160 Mbit/s DOCSIS 3.0 IPv6-ready specification for cable modems in August 2006. The widely used DOCSIS 2.0 does not support IPv6. The new 'DOCSIS 2.0 + IPv6' standard supports IPv6, which may on the cable modem side require only a firmware upgrade.[55][56] It is expected that only 60% of cable modems' servers and 40% of cable modems will be DOCSIS 3.0 by 2011.[57] However, most ISPs that support DOCSIS 3.0 do not support IPv6 across their networks. Other equipment which is typically not IPv6- ready ranges from Voice over Internet Protocol devices to laboratory equipment and printers.[citation needed] [edit]Deployment Main article: IPv6 deployment The introduction of Classless Inter-Domain Routing (CIDR) in the Internet routing and IP address allocation methods in 1993 and the extensive use of network address translation (NAT) delayed the inevitable IPv4 address exhaustion, but the final phase of exhaustion started on February 3, 2011.[15] However, despite a decade long development and implementation history as a Standards Track protocol, general worldwide deployment is still in its infancy. As of October 2011, about 3% of domain names and 12% of the networks on the internet have IPv6 protocol support.[58] IPv6 has been implemented on all major operating systems in use in commercial, business, and home consumer environments. Since 2008, the domain name system can be used in IPv6. IPv6 was first used in a major world event during the 2008 Summer Olympic Games,[59] the largest showcase of IPv6 technology since the inception of IPv6.[60] Countries like China or the Federal U.S. Government are also starting to require IPv6 capability on their equipment. Finally, modern cellular telephone specifications mandate IPv6 operation and deprecate IPv4 as an optional capability.[61]

IPv4

Follow Internet Protocol version 4 (IPv4) is the fourth revision in the development of the Internet Protocol (IP) and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet. As of 2012 IPv4 is still the most widely deployed Internet Layer protocol. IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980). IPv4 is a connectionless protocol for use on packet- switched Link Layer networks (e.g., Ethernet). It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol, such as the Transmission Control Protocol (TCP). IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4294967296 (2) addresses.

Clients and Servers In general, all of the machines on the Internet can be categorized as two types: servers and clients. Those machines that provide services (like Web servers or FTP servers) to other machines are servers. And the machines that are used to connect to those services are clients. When you connect to Yahoo! at www.yahoo.com to read a page, Yahoo! is providing a machine (probably a cluster of very large machines), for use on the Internet, to service your request. Yahoo! is providing a server. Your machine, on the other hand, is probably providing no services to anyone else on the Internet. Therefore, it is a user machine, also known as a client. It is possible and common for a machine to be both a server and a client, but for our purposes here you can think of most machines as one or the other. A server machine may provide one or more services on the Internet. For example, a server machine might have software running on it that allows it to act as a Web server, an e-mail server and an FTP server. Clients that come to a server machine do so with a specific intent, so clients direct their requests to a specific software server running on the overall server machine. For example, if you are running a Web browser on your machine, it will most likely want to talk to the Web server on the server machine. Your Telnetapplication will want to talk to the Telnet server, your e-mail application will talk to the e-mail server, and so on...

client/server  Reprints Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request. Although the client/server idea can be used by programs within a single computer, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common. For example, to check your bank account from your computer, a client program in your computer forwards your request to a server program at the bank. That program may in turn forward the request to its own client program that sends a request to a database server at another bank computer to retrieve your account balance. The balance is returned back to the bank data client, which in turn serves it back to the client in your personal computer, which displays the information for you.

The client/server model has become one of the central ideas of network computing. Most business applications being written today use the client/server model. So does the Internet's main program, TCP/IP. In marketing, the term has been used to distinguish distributed computing by smaller dispersed computers from the "monolithic" centralized computing of mainframe computers. But this distinction has largely disappeared as mainframes and their applications have also turned to the client/server model and become part of network computing.

In the usual client/server model, one server, sometimes called a daemon, is activated and awaits client requests. Typically, multiple client programs share the services of a common server program. Both client programs and server programs are often part of a larger program or application. Relative to the Internet, your Web browser is a client program that requests services (the sending of Web pages or files) from a Web server (which technically is called a Hypertext Transport Protocol or HTTP server) in another computer somewhere on the Internet. Similarly, your computer with TCP/IP installed allows you to make client requests for files from File Transfer Protocol (FTP) servers in other computers on the Internet.

Other program relationship models included master/slave, with one program being in charge of all other programs, and peer- to-peer, with either of two programs able to initiate a transaction. Getting started with client/servers

To explore how client/servers are used in the enterprise, here are some additional resources: How server virtualization improves efficiency in a client-server model: Here an experienced network expert explains how virtualization can optimize productivity in this expert response. Slow response times from client/server PC's running IFS applications: How do you find out the culprit of a network delays when you see little bandwidth being used? Read this Q&A to see what an experienced network administrating expert has to say.

RELATED GLOSSARY TERMS: virtual area network (VAN), 10- high-day busy period (10HD busy period), graceful degradation, online, softswitch, maximum transmission unit (MTU), traffic shaping (packet shaping), Dialed Number Identification Service (DNIS), WATS (wide-area telephone service), mail user agent (MUA)

Perbezaan antara 3G vs 4G Edisi ke-2 1:03 PM Syed Mohd Nooh No comments Jawapan: Bagaikan "tsunami" atau empohan maklumat mengenai kedatang teknologi internet 4G, ramai pelangan dan pengguna tertanya-tanya tentang apa sebenarnya perbezaan antara rangkain 4G yang baru dengan rangkaian 3G yang sudah semakin mendapat tempat di hati penguna tegar teknologi tanpa wayar. Jika kita perhatikan, iklan tentang kelajuan yang lebih tinggi dan pantas sering di paparkan tanpa memberitahu kepada penguna tentang penjeleasan yang tepat. "Internet Provider" seperti Maxis, Celcom dan dsb pula jelas mengambil langkah tunggu dan lihat untuk menggunakan teknologi 4G ini dan tampaknya kurang yakin akan keperluan untuk pengguna untuk menerokai teknologi 4G. Pengeluar telefon bimbit pula sering membuat perbandingan dengan persaing-pesaing mereka dengan mengunakan teknologi yang belum "matang" dan masih samar- samar.

Cara yang paling mudah untuk menjelaskan perbezaan antara 3G dan 4G ini boleh di jelaskan dengan membuat analisis yang mudah tentang tujuan utama kenapa teknologi ini dicipta. Generasi ketiga atau 3G (3rd Generation) internet tanpa wayar ini direka berdasarkan teknologi yang pada peringkat awalnya di reka untuk tujuan membuat panggilan telefon. Oleh kerana panggilan telefon memerlukan penghantaran jumlah data yang kurang besar berbanding melayari intenet, ciptaan teknologi internet 3G hanya bertujuan untuk menanangi keperluan penghantaran atau pemindahan jumlah data dengan kelajuan yang sederhana tidak seperti keperluan untuk memindahkan jumlah data yang besar untuk menonton video streaming di internet. Ini sebabnya telefon yang berteknologi 3G di pasaran adakalanya bermasalah ketika pengguna cuba untuk mengakses video streaming atau laman web yang mempunya jumlah datan yang besar.

Untuk menyahut cabaran arus penggunaan internet tanpa wayar dan juga keperluan pengguna tegar internet, terciptanya 4G internet tanpa wayar, direka untuk komunikasi yang merangkumi pemindahan data yang lebih banyak dari panggilan telefon. Pengendalian kemudahan panggilan telefon boleh di anggap terlalu mudah dengan ada teknologi 4G, kerana teknologi ini memang direka untuk komunikasi internet, streaming video, menonton televisyen dan setiap tugas yang sebelum ini hanya boleh dilakukan jika pengguna mempunyai sambungan selaju DSL; kini boleh di lakukan dengan telefon pada rangkaian 4G.

Salah satu perbezaan yang ketara antara rangkaian 3G dan 4G adalah kelajuan muat turun yang ditawarkan. Kelajuan muat turun pada rangkaian 3G umumnya sekitar 0.6 - 1.4 Megabits sesaat, dengan maksimum kelajuan 3.1 Megabits sesaat pada waktu tertentu. Untuk rangkaian 4G pula, ianya menawarkan kelajuan muat turun antara 3 - 6 Megabits sesaat, dengan maksimum kelajuan 10 Megabits sesaat, 3 -5 kali ganda kelajuan maksimum yang boleh di capai dari rangkaian generasi ketiga (3G).

Perbezaan lain yang boleh di ambil kira adalah perbezaan muat naik antara kedua-dua rankaian tersebut. Contohnya, untuk muak naik video atau fail dari computer ke laman web, rangkaian 3G menawarkan kelajuan hanya pada 0.5 Megabit berbanding 1 Megabits dengan menggunakan rangkaian 4G. Boleh di katakan rangkaian 4G boleh memuat naik dua kali ganda kepantasan rangkaian 3G.

Contoh lain kelajuan rangkaian 4G, jika muat turun rancangan televisyen mengambil masa kira-kira 19 minit pada rangkaian 3G, namun ianya mengambil kurang dari 5 minit jika menggunakan rangkaian 4G. Selain dari itu, membuat tempahan makan malam hanya mengambil masa setengah saat pada rangkaian 4G, 5 saat jika menggunakan rangkaian 3G dan banyak lagi contoh-contoh lain tentang kelajuan teknologi 4G ini.

Semua ini bermakna bahawa 4G internet tanpa wayar akan membolehkan pengguna untuk mengakses internet pada telefon mereka pada kelajuan yang sama jika mereka lakukan di rumah menggunakan DSL. Boleh di katakan, teknologi 4G pada telefon makin menghampiri kelajuan jika menggunakan computer biasa. Mungkin pada masa hadapan kita tidak perlu lagi bergantung kepada computer untuk melayari internet dengan patas, kita hanya memerlukan telefon yang dilengkapi dengan teknologi 4G sahaja.

Kepada mereka yang ingin tahu lebih mendalam tentang teknologi ini, boleh rujuk jadual di bawah.

Dates Cool New Features

70's to Telefon bimbit diperkenalkan, 1G 80's terutamanya untuk suara sahaja. Peningkatan prestasi dengan membolehkan pengguna pada 90's to satu saluran pada satu masa. 2G 2000 Semakin banyak telefon bimbit digunakan untuk pemindahan data dan suara. Internet berubah dengan fokus terhadap penghantaran 2001- data."Enhanced multimedia dan 2.5G 2004 "video streaming" menjadi kenyataan. Telefon boleh melayar laman web tetapi terhad. Kebolehan untuk menggunakan "Enhanced multimedia" dan "video streaming" semakin meningkat. 2004- 3G Standard dicipta untuk 2005 membolehkan akses universal dan mudah alih antara peranti yang berlainan (Telefon, PDA, dll) Kelajuan mencapai hingga 40Mbps. Keupayaan untuk menggunakan "Enhanced 4G 2006+ multimedia" dan "video streaming" semakin meningkat. Peranti dilengkapi untuk "roaming" di seluruh dunia.

Technology

1G Analog CMRT AMPS Digital Circuit D- 2G GSM CDMA Switched AMPS Digital Packet 2.5G GPRS EDGE Switched Digital Packet W- 3G UMTS CDMA2000 Switched CDMA 4G Digital Broadband 802.11

Data Rate

1G 9.6 Kbps to 14.4 Kbps D-AMPS 9.6 Kbps to 14.4 Kbps GSM 9.6 Kbps to 14.4 Kbps 2G IS95A 9.6 Kbps to 14.4 Kbps IS95B 115 Kbps 2.5G 56 Kbps to 144 Kbps UMTS 2+ Mbps, up to 384 Kbps 384 Kbps (wide area access), 2 3G WCDMA Mbps (local area access) CDMA2000 614 Kbps 4G 20-40 Mbps

The differences between social media and social networking are just about as vast as night and day. There are some key differences and knowing what they are can help you gain a better understanding on how to leverage them for your brand and business. 1. By Any Definition Social media is a way to transmit, or share information with a broad audience. Everyone has the opportunity to create and distribute. All you really need is an internet connection and you're off to the races. On the other hand, social networking is an act of engagement. Groups of people with common interests, or like-minds, associate together on social networking sites and build relationships through community. 2. Communication Style Social media is more akin to a communication channel. It's a format that delivers a message. Like television, radio or newspaper, social media isn't a location that you visit. Social media is simply a system that disseminates information ‘to' others. With social networking, communication is two-way. Depending on the topic, subject matter or atmosphere, people congregate to join others with similar experiences and backgrounds. Conversations are at the core of social networking and through them relationships are developed. 3. Return on Investment It can be difficult to obtain precise numbers for determining the ROI from social media. How do you put a numeric value on the buzz and excitement of online conversations about your brand, product or service? This doesn't mean that ROI is null, it just means that the tactics used to measure are different. For instance, influence, or the depth of conversation and what the conversations are about, can be used to gauge ROI. Social networking's ROI is a bit more obvious. If the overall traffic to your website is on the rise and you're diligently increasing your social networking base, you probably could attribute the rise in online visitors to your social efforts. 4. Timely Responses Social media is hard work and it takes time. You can't automate individual conversations and unless you're a well-known and established brand, building a following doesn't happen overnight. Social media is definitely a marathon and not a sprint. Because social networking is direct communication between you and the people that you choose connect with, your conversations are richer, more purposeful and more personal. Your network exponentially grows as you meet and get introduced to others. 5. Asking or Telling A big no-no on with social media is skewing or manipulating comments, likes, diggs, stumbles or other data, for your own benefit (personal or business). Asking friends, family, co-workers or anyone else to cast a vote just to cast it, doesn't do anyone much good for anyone and it can quickly become a PR nightmare if word leaks out about dishonest practices. With social networking, you can tell your peers about your new business or blog and discuss how to make it a success. The conversations that you create can convert many people into loyal fans, so it's worth investing the time. Social media and social networking do have some overlap, but they really aren't the same thing. Knowing that they're two separate marketing concepts can make a difference in how you position your business going forward. Share your thoughts or add a comment or two. We'd love to hear from you.

Institute of Electrical and Electronics Engineers From Wikipedia, the free encyclopedia "IEEE" redirects here. It is not to be confused with the Institution of Electrical Engineers (IEE). The Institute of Electrical and Electronics Engineers (IEEE, read I-Triple-E) is a non- profit professional association headquartered in New York Citythat is dedicated to advancing technological innovation and excellence. It has more than 400,000 members in more than 160 countries, about 51.4% of whom reside in the United States.[2][3] [edit]History

The IEEE corporate office is on the 17th floor of 3 Park Avenue in New York City The IEEE is incorporated under the Not-for-Profit Corporation Law of the state of New York in the United States.[4] It was formed in 1963 by the merger of the Institute of Radio Engineers (IRE, founded 1912) and the American Institute of Electrical Engineers (AIEE, founded 1884). The major interests of the AIEE were wire communications (telegraphy and telephony) and light and power systems. The IRE concerned mostly radioengineering, and was formed from two smaller organizations, the Society of Wireless and Telegraph Engineers and the Wireless Institute. With the rise of electronics in the 1930s, electronics engineers usually became members of the IRE, but the applications of electron tube technology became so extensive that the technical boundaries differentiating the IRE and the AIEE became difficult to distinguish. After World War II, the two organizations became increasingly competitive, and in 1961, the leadership of both the IRE and the AIEE resolved to consolidate the two organizations. The two organizations formally merged as the IEEE on January 1, 1963. Notable Presidents of IEEE and its founding organizations include Elihu Thomson (AIEE, 1889–1890), Alexander Graham Bell (AIEE, 1891–1892),Charles Proteus Steinmetz (AIEE, 1901–1902), Lee De Forest (IRE, 1930), Frederick E. Terman (IRE, 1941), William R. Hewlett (IRE, 1954), Ernst Weber (IRE, 1959; IEEE, 1963), and Ivan Getting (IEEE, 1978). IEEE's Constitution defines the purposes of the organization as "scientific and educational, directed toward the advancement of the theory and practice of Electrical, Electronics, Communications and Computer Engineering, as well as Computer Science, the allied branches of engineering and the relatedarts and sciences."[1] In pursuing these goals, the IEEE serves as a major publisher of scientific journals and organizer of conferences, workshops, and symposia (many of which have associated published proceedings). It is also a leading standards development organization for the development of industrial standards (having developed over 900 active industry technical standards) in a broad range of disciplines, including electric power and energy,biomedical technology and healthcare, information technology, information assurance, telecommunications, consumer electronics, transportation, aerospace, and nanotechnology. IEEE develops and participates in educational activities such as accreditation of electrical engineering programs in institutes of higher learning. The IEEE logo is a diamond- shaped design which illustrates the right hand grip rule embedded in Benjamin Franklin's kite, and it was created at the time of the 1963 merger. [5] IEEE has a dual complementary regional and technical structure – with organizational units based on geography (e.g., the IEEE Philadelphia Section, IEEE South Africa Section [1]) and technical focus (e.g., the IEEE Computer Society). It manages a separate organizational unit (IEEE- USA) which recommends policies and implements programs specifically intended to benefit the members, the profession and the public in the United States. The IEEE includes 38 technical Societies, organized around specialized technical fields, with more than 300 local organizations that hold regular meetings. The IEEE Standards Association is in charge of the standardization activities of the IEEE. [edit]Publications Main article: List of IEEE publications IEEE produces 30% of the world's literature in the electrical and electronics engineering and computer science fields, publishing well over 100 peer-reviewed journals.[6] The published content in these journals as well as the content from several hundred annual conferences sponsored by the IEEE are available in the IEEE online digital library for subscription-based access and individual publication purchases.[7] In addition to journals and conference proceedings, the IEEE also publishes tutorials and the standards that are produced by its standardization committees. [edit]Educational activities

Picture of the place where an office of IEEE works in the District University of Bogotá, Colombia. The IEEE provides learning opportunities within the engineering sciences, research, and technology. The goal of the IEEE education programs is to ensure the growth of skill and knowledge in the electricity-related technical professions and to foster individual commitment to continuing education among IEEE members, the engineering and scientific communities, and the general public. IEEE offers educational opportunities such as IEEE eLearning Library,[8] the Education Partners Program,[9] Standards in Education[10] and Continuing Education Units (CEUs).[11] IEEE eLearning Library is a collection of online educational courses designed for self-paced learning. Education Partners, exclusive for IEEE members, offers on-line degree programs, certifications and courses at a 10% discount. The Standards in Education website explains what standards are and the importance of developing and using them. The site includes tutorial modules and case illustrations to introduce the history of standards, the basic terminology, their applications and impact on products, as well as news related to standards, book reviews and links to other sites that contain information on standards. Currently, twenty-nine states in the United States require Professional Development Hours (PDH) to maintain a Professional Engineering license, encouraging engineers to seek Continuing Education Units (CEUs) for their participation in continuing education programs. CEUs readily translate into Professional Development Hours (PDHs), with 1 CEU being equivalent to 10 PDHs. Countries outside the United States, such as South Africa, similarly require continuing professional development (CPD) credits, and it is anticipated that IEEE Expert Now courses will feature in the CPD listing for South Africa. IEEE also sponsors a website[12] designed to help young people understand better what engineering means, and how an engineering career can be made part of their future. Students of age 8–18, parents, and teachers can explore the site to prepare for an engineering career, ask experts engineering-related questions, play interactive games, explore curriculum links, and review lesson plans. This website also allows students to search for accredited engineering degree programs in Canada and the United States; visitors are able to search by state/province/territory, country, degree field, tuition ranges, room and board ranges, size of student body, and location (rural, suburban, or urban). [edit]Standards and development process Main article: IEEE Standards Association IEEE is one of the leading standards-making organizations in the world. IEEE performs its standards making and maintaining functions through the IEEE Standards Association (IEEE-SA). IEEE standards affect a wide range of industries including: power and energy, biomedical and healthcare, Information Technology (IT), telecommunications, transportation, nanotechnology, information assurance, and many more. In 2005, IEEE had close to 900 active standards, with 500 standards under development. One of the more notable IEEE standards is the IEEE 802 LAN/MAN group of standards which includes the IEEE 802.3 Ethernet standard and the IEEE 802.11 Wireless Networking standard. [edit]Membership and member grades Most IEEE members are electrical and electronics engineers, but the organization's wide scope of interests has attracted people in other disciplines as well (e.g., computer science, mechanicaland civil engineering) as well as biologists, physicists, and mathematicians. An individual can join the IEEE as a student member, professional member, or associate member. In order to qualify for membership, the individual must fulfil certain academic or professional criteria and abide to the code of ethics and bylaws of the organization. There are several categories and levels of IEEE membership and affiliation:

. Student Members: Student membership is available for a reduced fee to those who are enrolled in an accredited institution of higher education as undergraduate or graduate students in technology or engineering. . Members: Ordinary or professional Membership requires that the individual have graduated from a technology or engineering program of an appropriately accredited institution of higher education or have demonstrated professional competence in technology or engineering through at least six years of professional work experience. An associate membership is available to individuals whose area of expertise falls outside the scope of the IEEE or who does not, at the time of enrollment, meet all the requirements for full membership. Students and Associates have all the privileges of members, except the right to vote and hold certain offices. . Society Affiliates: Some IEEE Societies also allow a person who is not an IEEE member to become a Society Affiliate of a particular Society within the IEEE, which allows a limited form of participation in the work of a particular IEEE Society. . Senior Members: Upon meeting certain requirements, a professional member can apply for Senior Membership, which is the highest level of recognition that a professional member can directly apply for. Applicants for Senior Member must have at least three letters of recommendation from Senior, Fellow, or Honorary members and fulfill other rigorous requirements of education, achievement, remarkable contribution, and experience in the field. The Senior Members are a selected group, and certain IEEE officer positions are available only to Senior (and Fellow) Members. Senior Membership is also one of the requirements for those who are nominated and elevated to the grade IEEE Fellow, a distinctive honor. . Fellow Members: The Fellow grade of membership is the highest level of membership, and cannot be applied for directly by the member – instead the candidate must be nominated by others. This grade of membership is conferred by the IEEE Board of Directors in recognition of a high level of demonstrated extraordinary accomplishment. . Honorary Members: Individuals who are not IEEE members but have demonstrated exceptional contributions, such as being a recipient of an IEEE Medal of Honor, may receive Honorary Membership from the IEEE Board of Directors. . Life Members and Life Fellows: Members who have reached the age of 65 and whose number of years of membership plus their age in years adds up to at least 100 are recognized as Life Members – and, in the case of Fellow members, as Life Fellows. [edit]Awards Through its awards program, the IEEE recognizes contributions that advance the fields of interest to the IEEE. For nearly a century, the IEEE Awards Program has paid tribute to technical professionals whose exceptional achievements and outstanding contributions have made a lasting impact on technology, society and the engineering profession. Funds for the awards program, other than those provided by corporate sponsors for some awards, are administered by the IEEE Foundation. [edit]Medals

. IEEE Medal of Honor . IEEE Edison Medal . IEEE Founders Medal (for leadership, planning, and administration) . IEEE James H. Mulligan, Jr. Education Medal . IEEE Alexander Graham Bell Medal (for communications engineering) . IEEE Simon Ramo Medal (for systems engineering) . IEEE Medal for Engineering Excellence . IEEE Medal for Environmental and Safety Technologies . IEEE Medal in Power Engineering . IEEE Richard W. Hamming Medal (for information technology) . IEEE Heinrich Hertz Medal (for electromagnetics) . IEEE John von Neumann Medal (for computer-related technology) . IEEE Jack S. Kilby Signal Processing Medal . IEEE Dennis J. Picard Medal for Radar Technologies and Applications . IEEE Robert N. Noyce Medal (for microelectronics) . IEEE Medal for Innovations in Healthcare Technology . IEEE/RSE Wolfson James Clerk Maxwell Award . IEEE Centennial Medal [edit]Technical field awards

. IEEE Biomedical Engineering Award . IEEE Cledo Brunetti Award (for nanotechnology and miniaturization) . IEEE Components, Packaging, and Manufacturing Technologies Award . IEEE Control Systems Award . IEEE Electromagnetics Award . IEEE James L. Flanagan Speech and Audio Processing Award . IEEE Andrew S. Grove Award (for solid-state devices) . IEEE Herman Halperin Electric Transmission and Distribution Award . IEEE Masaru Ibuka Consumer Electronics Award . IEEE Internet Award . IEEE Reynold B. Johnson Data Storage Device Technology Award . IEEE Reynold B. Johnson Information Storage Systems Award . IEEE Richard Harold Kaufmann Award (for industrial systems engineering) . IEEE Joseph F. Keithley Award in Instrumentation and Measurement . IEEE Gustav Robert Kirchhoff Award (for electronic circuits and systems) . IEEE Leon K. Kirchmayer Graduate Teaching Award . IEEE Koji Kobayashi Computers and Communications Award . IEEE William E. Newell Power Electronics Award . IEEE Daniel E. Noble Award (for emerging technologies) . IEEE Donald O. Pederson Award in Solid-State Circuits . IEEE Frederik Philips Award (for management of research and development) . IEEE Photonics Award . IEEE Emanuel R. Piore Award (for information processing systems in computer science) . IEEE Judith A. Resnik Award (for space engineering) . IEEE Robotics and Automation Award . IEEE Frank Rosenblatt Award (for biologically and linguistically motivated computational paradigms such as neural networks . IEEE David Sarnoff Award (for electronics) . IEEE Charles Proteus Steinmetz Award (for standardization) . IEEE Marie Sklodowska-Curie Award (for nuclear and plasma engineering) . IEEE Eric E. Sumner Award (for communications technology) . IEEE Undergraduate Teaching Award . IEEE Nikola Tesla Award (for power technology) . IEEE Kiyo Tomiyasu Award (for technologies holding the promise of innovative applications) [edit]Recognitions

. IEEE Haraden Pratt Award . IEEE Richard M. Emberson Award . IEEE Corporate Innovation Recognition . IEEE Ernst Weber Engineering Leadership Recognition . IEEE Honorary Membership [edit]Prize paper awards

. IEEE Donald G. Fink Prize Paper Award . IEEE W.R.G. Baker Award [edit]Scholarships

. IEEE Life Members Graduate Study Fellowship in Electrical Engineering was established by the IEEE in 2000. The fellowship is awarded annually to a first year, full time graduate student obtaining their masters for work in the area of electrical engineering, at an engineering school/program of recognized standing worldwide.[13] . IEEE Charles LeGeyt Fortescue Graduate Scholarship was established by the IRE in 1939 to commemorate Charles Legeyt Fortescue's contributions to electrical engineering. The scholarship is awarded for one year of full-time graduate work obtaining their masters in electrical engineering an ANE engineering school of recognized standing in the United States.[14] [edit]Societies IEEE is supported by 38 societies, each one focused on a certain knowledge area. They provide specialized publications, conferences, business networking and sometimes other services.[15][16]

. IEEE Aerospace and Electronic Systems Society . IEEE Instrumentation & Measurement Society . IEEE Antennas & Propagation Society . IEEE Intelligent Transportation Systems Society . IEEE Broadcast Technology Society . IEEE Magnetics Society . IEEE Circuits and Systems Society . IEEE Microwave Theory and Techniques Society . IEEE Communications Society . IEEE Nuclear and Plasma Sciences Society . IEEE Components, Packaging & Manufacturing . IEEE Oceanic Engineering Society Technology Society . IEEE Photonics Society . IEEE Computational Intelligence Society . IEEE Power Electronics Society . IEEE Computer Society . IEEE Power & Energy Society . IEEE Consumer Electronics Society . IEEE Product Safety Engineering Society . IEEE Control Systems Society . IEEE Professional Communication Society . IEEE Dielectrics & Electrical Insulation Society . IEEE Reliability Society . IEEE Education Society . IEEE Robotics and Automation Society . IEEE Electromagnetic Compatibility Society . IEEE Signal Processing Society . IEEE Electron Devices Society . IEEE Society on Social Implications of Technology . IEEE Engineering in Medicine and Biology Society . IEEE Solid-State Circuits Society . IEEE Geoscience and Remote Sensing Society . IEEE Systems, Man & Cybernetics Society . IEEE Industrial Electronics Society . IEEE Ultrasonics, Ferroelectrics & Frequency Control . IEEE Industry Applications Society Society . IEEE Information Theory Society . IEEE Vehicular Technology Society [edit]Technical councils IEEE technical councils are collaborations of several IEEE societies on a broader knowledge area. There are currently seven technical councils:[15][17]

. IEEE Biometrics Council . IEEE Council on Electronic Design Automation . IEEE Nanotechnology Council . IEEE Sensors Council . IEEE Council on Superconductivity . IEEE Systems Council . IEEE Technology Management Council [edit]Technical committees To allow a quick response to new innovations, IEEE can also organize technical committees on top of their societies and technical councils. There are currently two such technical committees:[15]

. IEEE Committee on Earth Observation (ICEO) . IEEE Technical Committee on RFID (CRFID) [edit]Organizational units

. Technical Activities Board (TAB) [edit]IEEE Foundation The IEEE Foundation is a charitable foundation established in 1973 to support and promote technology education, innovation and excellence.[18] It is incorporated separately from the IEEE, although it has a close relationship to it. Members of the Board of Directors of the foundation are required to be active members of IEEE, and one third of them must be current or former members of the IEEE Board of Directors. Initially, the IEEE Foundation's role was to accept and administer donations for the IEEE Awards program, but donations increased beyond what was necessary for this purpose, and the scope was broadened. In addition to soliciting and administering unrestricted funds, the foundation also administers donor-designated funds supporting particular educational, humanitarian, historical preservation, and peer recognition programs of the IEEE.[18] As of the end of 2009, the foundation's total assets were $27 million, split equally between unrestricted and donor-designated funds.[19] [edit]Copyright policy The IEEE requires authors to transfer their copyright for works they submit for publication.[20][21] The IEEE generally does not create its own research. It is a professional organization that coordinates journal peer- review activities and holds subject-specific conferences in which authors present their research. The IEEE then publishes the authors' papers in journals and other proceedings, and authors are required to give up their exclusive rights to their works.[20] Section 6.3.1 IEEE Copyright Policies – subsections 7 and 8 – states that "all authors…shall transfer to the IEEE in writing any copyright they hold for their individual papers", but that the IEEE will grant the authors permission to make copies and use the papers they originally authored, so long as such use is permitted by the Board of Directors. The guidelines for what the Board considers a "permitted" use are not entirely clear, although posting a copy on a personally controlled website is allowed. The author is also not allowed to change the work absent explicit approval from the organization. The IEEE justifies this practice in the first paragraph of that section, by stating that they will "serve and protect the interests of its authors and their employers".[20][21] The IEEE places research papers and other publications such as IEEE standards behind a "pay wall"[20], although the IEEE explicitly allows authors to make a copy of the papers that they authored freely available on their own website. As of September 2011, the IEEE also provides authors for most new journal papers with the option to pay to allow free download of their papers by the public from the IEEE publication website.[22] IEEE publications have received a Green[23] rating the from SHERPA/RoMEO guide[24] for affirming "authors and/or their companies shall have the right to post their IEEE-copyrighted material on their own servers without permission" (IEEE Publication Policy 8.1.9.D[25]). This open access policy effectively allows authors, at their choice, to make their article openly available. Roughly 1/3 of the IEEE authors take this route[citation needed]. Some other professional associations do not impose the same requirements on authors. For example, the USENIX association[20] requires that the author only give up the right to publish the paper elsewhere for 12 months (in addition to allowing authors to post copies of the paper on their own website during that time). The organization operates successfully even though all of its publications are freely available online.[20] Institut Jurutera Elektrik dan Elektronik (IEEE) Institut Elektrik dan Elektronik Jurutera Standards Association (IEEE-SA) adalah pemaju utama piawaian industri global dalam pelbagai industri, termasuk Teknologi Maklumat, Kuasa dan Tenaga, Telekomunikasi, Pengangkutan, Perubatan dan Kesihatan dan Piawaian baru dan teknologi baru muncul seperti Nanoteknologi. Di samping itu, untuk memajukan teori dan amalan elektrik, elektronik dan komputer kejuruteraan dan sains komputer, IEEE menaja persidangan dan simposium dan mesyuarat dan menerbitkan kertas kerja teknikal penting dan standard. IEEE membangunkan menonjol 802 ® Standard untuk Kawasan Tempatan dan Rangkaian Wireless Metropolitan dan rangkaian berwayar. 802 standard ® boleh didapati untuk muat turun bebas dari Get IEEE 802 laman web ®.

IEEE mempunyai 42 masyarakat teknikal dan majlis-majlis teknikal yang banyak yang telah kumpulan yang bekerjasama secara aktif untuk membangunkan standard. Berikut adalah senarai beberapa kumpulan utama yang mempunyai laman web awam dilihat.

Masyarakat IEEE Komunikasi Ia adalah sebuah komuniti yang terdiri daripada pelbagai kumpulan profesional industri dengan kepentingan bersama dalam memajukan semua teknologi komunikasi. Persatuan menaja penerbitan, persidangan, program pendidikan, aktiviti tempatan, jawatankuasa teknikal, dan standard. Masyarakat IEEE Komputer Antara aktiviti teknikal yang banyak, ia mempunyai pembangunan standard yang sangat aktif organisasi yang diketuai oleh Lembaga Piawaian Aktiviti (BPS) yang menyediakan satu rangka kerja organisasi dan persekitaran yang kondusif dalam mana untuk membangunkan secara meluas diterima, standard bunyi, tepat pada masanya, dan teknikal yang cemerlang yang akan memajukan teori dan amalan sains dan teknologi pemprosesan komputer dan maklumat. Masyarakat IEEE EMC IEEE Society Keserasian Elektromagnetik (EMC) adalah pemaju utama antarabangsa ujian asas dan standard pengukuran untuk EMC IEEE Power Engineering Society Seperti masyarakat kakak, ia menaja penerbitan, persidangan, aktiviti-aktiviti pendidikan, jawatankuasa teknikal dan standard. Fokus standard adalah penjanaan, penghantaran dan pengagihan kuasa elektrik. Jawatankuasa Standard IEEE 802 membangunkan standard Rangkaian Kawasan Tempatan dan Rangkaian Kawasan Metropolitan standard. Piawaian yang paling banyak digunakan adalah untuk keluarga Ethernet, Token Ring, Wireless LAN, Merapatkan dan Maya menghubungkan LAN. Satu Kumpulan Kerja individu memberikan fokus untuk setiap kawasan.

IEEE juga menawarkan pelbagai bahan pada proses pembangunan standard. Berikut adalah beberapa berguna Web:

IEEE Piawaian Pembangunan Online (menyediakan panduan lengkap langkah demi langkah untuk membangunkan Standard IEEE) IEEE SA Latihan Persembahan (Pembentangan Latihan IEEE- SA)

4G From Wikipedia, the free encyclopedia This article is about the mobile telecommunications standard. For other uses, see 4G (disambiguation). This article may be too technical for most readers to understand. Please help improve this article to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (December 2011) In telecommunications, 4G is the fourth generation of cell phone mobile communications standards. It is a successor of the third generation (3G) standards. A 4G system provides mobile ultra-broadband Internet access, for example to laptops with USB wireless modems, to smartphones, and to other mobile devices. Conceivable applications include amended mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing and 3D television. Two 4G candidate systems are commercially deployed: The Mobile WiMAX standard (at first in South Korea in 2006), and the first-release Long term evolution (LTE) standard (in Scandinavia since 2009). It has however been debated if these first-release versions should be considered as 4G or not. See technical definition. In the U.S. Sprint Nextel has deployed Mobile WiMAX networks since 2008, and MetroPCS was the first operator to offer LTE service in 2010. USB wireless modems have been available since the start, while WiMAX smartphones have been available since 2010, and LTE smartphones since 2011. Equipment made for different continents are not always compatible, because of different frequency bands. Mobile WiMAX and LTE smartphones are currently (April 2012) not available for the European market. [edit]Technical definition In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 100 megabits per second (Mbit/s) for high mobility communication (such as from trains and cars) and 1 gigabit per second (Gbit/s) for low mobility communication (such as pedestrians and stationary users).[1] Since the above mentioned first-release versions of Mobile WiMAX and LTE support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers. On December 6, 2010, ITU-R recognized that these two technologies, as well as other beyond-3G technologies that do not fulfill the IMT-Advanced requirements, could nevertheless be considered "4G", provided they represent forerunners to IMT-Advanced compliant versions and "a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed".[2] Mobile WiMAX Release 2 (also known as WirelessMAN- Advanced or IEEE 802.16m') and LTE Advanced (LTE-A) are IMT-Advanced compliant backwards compatible versions of the above two systems, standardized during the spring 2011,[citation needed] and promising peak bit rates in the order of 1 Gbit/s. Services are expected in 2013.[3] As opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but all-Internet Protocol (IP) based communication such as IP telephony. As seen below, the spread spectrum radio technology used in 3G systems, is abandoned in all 4G candidate systems and replaced by OFDMA multi- carrier transmission and other frequency-domain equalization (FDE) schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation (echoes). The peak bit rate is further improved by smart antennaarrays for multiple-input multiple-output (MIMO) communications. Finally, the term "generation" used to name successive evolutions of radio networks in general is arbitrary. There are several interpretations of it, and no official definition despite the large consensus behind ITU-R's labels. As you can read along this article, a comment is made about the legitimate use of the term almost each time it is used. From the point of view of ITU-R, 4G is equivalent to IMT- Advanced which has specific performance requirements as explained below. But from the point of view of operators, a generation of network refers to the deployment of a new non-backward compatible technology. This usually corresponds to a huge investment with its own depreciation period, marketing strategy (if any), and deployment phases. It can even be different among operators. From the end user point of view, only performance makes sense. We expect that the next generation of network performs better than the previous one which is not that simple to state. Indeed while a new generation of network arrives, the previous one keeps evolving to a point where it outperforms the first version of the new generation. In many countries, GSM, UMTS and LTE networks still coexist. It is thus much less ambiguous to use the name of the technology/standard, possibly followed by its version number, than a subjective arbitrary generation number which is destined to be challenged endlessly. [edit]Background The nomenclature of the generations generally refers to a change in the fundamental nature of the service, non- backwards-compatible transmission technology, higher peak bitrates, new frequency bands, wider channel frequency bandwidth in Hertz, and higher capacity for many simultaneous data transfers (higher system spectral efficiency in bit/second/Hertz/site). New mobile generations have appeared about every ten years since the first move from 1981 analog (1G) to digital (2G) transmission in 1992. This was followed, in 2001, by 3G multi-media support, spread spectrum transmission and at least 200 kbit/s peak bitrate, in 2011/2012 expected to be followed by "real" 4G, which refers to all-Internet Protocol (IP) packet-switched networks giving mobile ultra- broadband (gigabit speed) access. While the ITU has adopted recommendations for technologies that would be used for future global communications, they do not actually perform the standardization or development work themselves, instead relying on the work of other standards bodies such as IEEE, The WiMAX Forum and 3GPP. In mid 1990s, the ITU-R standardization organization released the IMT-2000 requirements as a framework for what standards should be considered 3G systems, requiring 200 kbit/s peak bit rate. In 2008, ITU-R specified the IMT-Advanced (International Mobile Telecommunications Advanced) requirements for 4G systems. The fastest 3G-based standard in the UMTS family is the HSPA+ standard, which was commercially available in 2009 and offers 28 Mbit/s downstreams (22 Mbit/s upstreams) without MIMO, i.e. only with one antenna, and in 2011 accelerated up to 42 Mbit/s peak bit rate downstreams using either DC-HSPA+ (simultaneous use of two 5 MHz UMTS carrier)[4] or 2x2 MIMO. In theory 672 Mbit/s is possible, but still not deployed. The fastest 3G- based standard in the CDMA2000 family is the EV-DO Rev. B, which was available in 2010 and offers 15.67 Mbit/s downstreams.[citation needed] [edit]IMT-Advanced Requirements This article uses 4G to refer to IMT-Advanced (International Mobile Telecommunications Advanced), as defined by ITU-R. An IMT-Advanced cellular system must fulfill the following requirements:[5] . Based on an all-IP packet switched network. . Peak data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access. . Dynamically share and use the network resources to support more simultaneous users per cell. . Scalable channel bandwidth 5–20 MHz, optionally up to 40 MHz.[6][7] . Peak link spectral efficiency of 15 bit/s/Hz in the downlink, and 6.75 bit/s/Hz in the uplink (meaning that 1 Gbit/s in the downlink should be possible over less than 67 MHz bandwidth). . System spectral efficiency of up to 3 bit/s/Hz/cell in the downlink and 2.25 bit/s/Hz/cell for indoor usage.[6] . Smooth handovers across heterogeneous networks. . Ability to offer high quality of service for next generation multimedia support. In September 2009, the technology proposals were submitted to the International Telecommunication Union (ITU) as 4G candidates.[8] Basically all proposals are based on two technologies:

. LTE Advanced standardized by the 3GPP . 802.16m standardized by the IEEE (i.e. WiMAX) Implementations of Mobile WiMAX and first-release LTE are largely considered a stopgap solution that will offer a considerable boost until WiMAX 2 (based on the 802.16m spec) and LTE Advanced are deployed. The latter standard versions were ratified in spring 2011, but are still far from being implemented.[5] The first set of 3GPP requirements on LTE Advanced was approved in June 2008.[9] LTE Advanced was to be standardized in 2010 as part of Release 10 of the 3GPP specification. LTE Advanced will be based on the existing LTE specification Release 10 and will not be defined as a new specification series. A summary of the technologies that have been studied as the basis for LTE Advanced is included in a technical report.[10] First release LTE and Mobile WiMAX implementations are in some sources considered pre-4G or near-4G, as they do not fully comply with the planned requirements of 1 Gbit/s for stationary reception and 100 Mbit/s for mobile. Confusion has been caused by some mobile carriers who have launched products advertised as 4G but which according to some sources are pre-4G versions, commonly referred to as '3.9G', which do not follow the ITU-R defined principles for 4G standards, but today can be called 4G according to ITU-R. A common argument for branding 3.9G systems as new-generation is that they use different frequency bands from 3G technologies; that they are based on a new radio-interface paradigm; and that the standards are not backwards compatible with 3G, whilst some of the standards are forwards compatible with IMT- 2000 compliant versions of the same standards. [edit]System standards [edit]IMT-2000 compliant 4G standards Recently, ITU-R Working Party 5D approved two industry- developed technologies (LTE Advanced and WirelessMAN-Advanced)[11] for inclusion in the ITU’s International Mobile Telecommunications Advanced (IMT- Advanced program), which is focused on global communication systems that would be available several years from now. [edit]LTE Advanced See also: 3GPP Long Term Evolution (LTE) below LTE Advanced (Long-term-evolution Advanced) is a candidate for IMT-Advanced standard, formally submitted by the 3GPP organization to ITU-T in the fall 2009, and expected to be released in 2012. The target of 3GPP LTE Advanced is to reach and surpass the ITU requirements.[12] LTE Advanced is essentially an enhancement to LTE. It is not a new technology but rather an improvement on the existing LTE network. This upgrade path makes it more cost effective for vendors to offer LTE and then upgrade to LTE Advanced which is similar to the upgrade from WCDMA to HSPA. LTE and LTE Advanced will also make use of additional spectrum and multiplexing to allow it to achieve higher data speeds. Coordinated Multi-point Transmission will also allow more system capacity to help handle the enhanced data speeds. Release 10 of LTE is expected to achieve the IMT Advanced speeds. Release 8 currently supports up to 300 Mbit/s download speeds which is still short of the IMT-Advanced standards.[13] Data speeds of LTE Advanced

LTE Advanced

Peak download 1 Gbit/s

Peak upload 500 Mbit/s [edit]IEEE 802.16m or WirelessMAN-Advanced The IEEE 802.16m or WirelessMAN- Advanced evolution of 802.16e is under development, with the objective to fulfill the IMT-Advanced criteria of 1 Gbit/s for stationary reception and 100 Mbit/s for mobile reception.[14] [edit]Forerunner versions [edit]3GPP Long Term Evolution (LTE) See also: LTE Advanced above

Telia-branded Samsung LTE modem The pre-4G technology 3GPP Long Term Evolution (LTE) is often branded "4G-LTE", but the first LTE release does not fully comply with the IMT- Advanced requirements. LTE has a theoretical net bit rate capacity of up to 100 Mbit/s in the downlink and 50 Mbit/s in the uplink if a 20 MHz channel is used — and more if multiple-input multiple-output (MIMO), i.e. antenna arrays, are used. The physical radio interface was at an early stage named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA). The first LTE USB dongles do not support any other radio interface. The world's first publicly available LTE service was opened in the two Scandinavian capitals Stockholm (Ericsson and Nokia Siemens Networkssystems) and Oslo (a Huawei system) on 14 December 2009, and branded 4G. The user terminals were manufactured by Samsung.[15] Currently, the three publicly available LTE services in the United States are provided by MetroPCS,[16] Verizon Wireless,[17] and AT&T. As of April 2012, US Cellular[18] also offers 4G LTE. Sprint Nextel has also stated it's considering switching from WiMax to LTE in the near future.[17] T-Mobile Hungary launched a public beta test (called friendly user test) on 7 October 2011, and offers commercial 4G LTE service since 1 January 2012.[citation needed] In South Korea, SK Telecom and LG U+ have enabled access to LTE service since 1 July 2011 for data devices, slated to go nationwide by 2012.[19]

Data speeds of LTE

LTE

Peak download 100 Mbit/s

Peak upload 50 Mbit/s

[edit]Mobile WiMAX (IEEE 802.16e) The Mobile WiMAX (IEEE 802.16e-2005) mobile wireless broadband access (MWBA) standard (also known as WiBro in South Korea) is sometimes branded 4G, and offers peak data rates of 128 Mbit/s downlink and 56 Mbit/s uplink over 20 MHz wide channels[citation needed]. In June 2006, the world's first commercial mobile WiMAX service was opened by KT in Seoul, South Korea.[20] Sprint Nextel has begun using Mobile WiMAX, as of September 29, 2008 branded as a "4G" network even though the current version does not fulfil the IMT Advanced requirements on 4G systems.[21] In Russia, Belarus and Nicaragua WiMax broadband internet access is offered by a Russian company Scartel, and is also branded 4G, Yota.

Data speeds of WiMAX

WiMAX

Peak download 128 Mbit/s

Peak upload 56 Mbit/s

[edit]TD-LTE for China Market Just when Long-Term Evolution (LTE) and WiMax vigorously promoting in the global telecommunications industry, the former (LTE) is also the most powerful 4G mobile communication leading technology, is a meteoric rise, and quickly occupied the Chinese market. Qualcomm and the Yota's TD- LTE is not yet mature, but many domestic and international wireless carriers one after another turn to TD-LTE. IBM data show that 67% of the operators are considering LTE, because this is the main source of their future market. The above news also confirmed this statement of IBM. While only 8% of the operators to consider the use of WiMAX. WiMax can provide the fastest network transmission to its customers on the market, but still not the rival of LTE. TD-LTE is not the first 4G wireless mobile broadband network data standard, it is China's 4G standard that amendmented and published by China's largest telecom operators - China Mobile. After a series of field trials, is expected into the commercial phase in the next two years . Ulf Ewaldsson, Ericsson's vice president said: "the Chinese Ministry of Industry and China Mobile in the fourth quarter of this year will hold a large-scale field test, by then, Ericsson will help the hand." But view from the current development trend, whether this standard advocated by China Mobile will be widely recognized by the international market, is still debatable. [edit]Discontinued candidate systems [edit]UMB (formerly EV-DO Rev. C) Main article: Ultra Mobile Broadband UMB (Ultra Mobile Broadband) was the brand name for a discontinued 4G project within the 3GPP2 standardization group to improve the CDMA2000 mobile phone standard for next generation applications and requirements. In November 2008, Qualcomm, UMB's lead sponsor, announced it was ending development of the technology, favouring LTE instead.[22] The objective was to achieve data speeds over 275 Mbit/s downstream and over 75 Mbit/s upstream. [edit]Flash-OFDM At an early stage the Flash-OFDM system was expected to be further developed into a 4G standard. [edit]iBurst and MBWA (IEEE 802.20) systems The iBurst system (or HC-SDMA, High Capacity Spatial Division Multiple Access) was at an early stage considered as a 4G predecessor. It was later further developed into the Mobile Broadband Wireless Access (MBWA) system, also known as IEEE 802.20. [edit]Data rate comparison The following table shows a comparison of 4G candidate systems as well as other competing technologies.

Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s) Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

HSPA+ is widely deployed . Revision 11 of the 3GPP 21 5.8 CDMA/F states Used 42 11.5

HSPA+ 3GPP DD that HSP in 4G 84 22 MIMO A+ is 672 168 expected to have a throughp ut capacity of 672 Mbps.

100 50 LTE- Genera OFDMA/

LTE 3GPP Cat3 Cat3/ Advance l 4G MIMO/S 150 4 d update Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

C-FDMA Cat4 75 expected 300 Cat5 to offer Cat5 (in 20 peak (in MHz rates up 20 MH FDD)[ to 1 z 23] Gbit/s FDD)[2 fixed 3] speeds and 100 Mb/s to mobile users.

37 17 Wirele MIMO- With 2x2 WiMax (10 M (10 M [2

802.16 ssMA SOFDM MIMO.

rel 1 Hz Hz N A 4] TDD) TDD)

83 46 With 2x2 WiMax 802.16 Wirele MIMO- (20 M (20 M MIMO.E

rel 1.5 -2009 ssMA SOFDM Hz Hz nhanced Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

N A TDD) TDD) with 141 138 20Mhz (2x20 (2x20 channels MHz MHz in FDD) FDD) 802.16- 2009[24]

2x2 2x2 MIMO MIM Also low 110 O mobility (20 M 70 users can Hz (20 M aggregat e Wirele MIMO- TDD) Hz WiMA 802.16 multiple ssMA SOFDM 183 TDD)

X rel 2 m channels N A (2x20 188 MHz (2x20 for up to FDD) MHz DL 4x4 FDD) throughp ut MIMO 4x4 [24] 219 MIM 1Gbps (20 M O Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

Hz 140(2 TDD) 0 MH 365 z (2x20 TDD) MHz 376 FDD) (2x20 MHz FDD)

Mobile Mobile Interne range t 30 km Flash- mobilit 5.3 1.8 (18 Flash- Flash- OFD y up to 10.6 3.6 miles)

OFDM OFDM M 200 mp 15.9 5.4 extended h range 55 (350 k km (34 m/h) miles)

HIPE Mobile HIPER OFDM 56.9 RMA Interne Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

MAN N t

Antenna, RF front end enha ncements and 288.8 (using minor 4x4 protocol configuration timer in 20 MHz Mobile tweaks 802.11 OFDM/ bandwidth) or have Wi-Fi Intern (11n) MIMO 600 (using et helped 4x4 deploy configuration long in 40 MHz range P2 bandwidth) P networ ks compro mising on radial coverage Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

, throughp ut and/or spectra efficienc y (310 km & 382 k m) Cell Radius: 3–12 km Speed: HC- 250 km/h Mobile SDMA/T Spectral

iBurst 802.20 Intern 95 36 DD/MIM Efficienc et O y: 13 bits/s/Hz /cell Spectru m Reuse Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

Factor: "1" EDGE Mobile TDMA/F 3GPP Re

Evoluti GSM Intern 1.6 0.5 DD lease 7

on et HSDPA is widely deployed . Typical downlink UMTS CDMA/F rates W- DD UMTS today 2 CDMA Genera 0.384 0.384 /3GS Mbit/s, HSDPA l 3G CDMA/F 14.4 5.76

M ~200 +HSUP DD/MIM kbit/s A O uplink; HSPA+ downlink up to 56 Mbit/s. UMTS- UMTS Mobile CDMA/T 16 Reported Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

TDD /3GS Interne DD speeds M t accordin g to IPWir eless usi ng 16QAM modulati on similar toHSDP A+HSU PA EV- Rev B DO Rel. note: N 0 is the Mobile 2.45 0.15 EV- CDM CDMA/F number Interne 3.1 1.8 DO Rev A2000 DD of 1.25 t 4.9xN 1.8xN .A MHz EV- chunks DO Rev of Comparison of Mobile Internet Access methods

Dow Ups Com Prim nstre trea Fam Radio mon ary am m Notes ily Tech Name Use (Mbi (Mb t/s) it/s)

.B spectrum used. EV-DO is not designed for voice, and requires a fallback to 1xRTT when a voice call is placed or received. Notes: All speeds are theoretical maximums and will vary by a number of factors, including the use of external antennae, distance from the tower and the ground speed (e.g. communications on a train may be poorer than when standing still). Usually the bandwidth is shared between several terminals. The performance of each technology is determined by a number of constraints, including the spectral efficiency of the technology, the cell sizes used, and the amount of spectrum available. For more information, see Comparison of wireless data standards. For more comparison tables, see bit rate progress trends, comparison of mobile phone standards, spectral efficiency comparison table and OFDM system comparison table. [edit]Principal technologies in all candidate systems [edit]Key features The following key features can be observed in all suggested 4G technologies:

. Physical layer transmission techniques are as follows:[25] . MIMO: To attain ultra high spectral efficiency by means of spatial processing including multi- antenna and multi-user MIMO . Frequency-domain-equalization, for example multi-carrier modulation (OFDM) in the downlink or single-carrier frequency-domain- equalization (SC-FDE) in the uplink: To exploit the frequency selective channel property without complex equalization . Frequency-domain statistical multiplexing, for example (OFDMA) or (single-carrier FDMA) (SC- FDMA, a.k.a. linearly precoded OFDMA, LP- OFDMA) in the uplink: Variable bit rate by assigning different sub-channels to different users based on the channel conditions . Turbo principle error-correcting codes: To minimize the required SNR at the reception side . Channel-dependent scheduling: To use the time- varying channel . Link adaptation: Adaptive modulation and error- correcting codes . Mobile-IP utilized for mobility . IP-based femtocells (home nodes connected to fixed Internet broadband infrastructure) As opposed to earlier generations, 4G systems does not support circuit switched telephony. Most[which?] 4G standards lack soft-handover support, also known as cooperative relaying. [edit]Multiplexing and Access schemes This section contains information which may be of unclear or questionable importance or relevance t o the article's subject matter. Please help improve this article by clarifying or removing superfluous information. (May 2010) The Migration to 4G standards incorporates elements of many early technologies and often you will read about solutions that use Code (a cypher), Frequency or Time as the basis of multiplexing the spectrum more efficiently. While Spectrum is considered finite, Cooper's Law has shown that we have developed more efficient ways of using spectrum just as the Moore's law has show our ability to increase processing. As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced an access scheme called CDMA. Usage of CDMA increased the system capacity, but as a theoretical drawback placed a soft limit on it rather than the hard limit (i.e. a CDMA network setup does not inherently reject new clients when it approaches its limits, resulting in a denial of service to all clients when the network overloads; though this outcome is avoided in practical implementations by admission control of circuit switched or fixed bitrate communication services). Data rate is also increased as this access scheme (providing the network is not reaching its capacity) is efficient enough to handle the multipath channel. This enabled the third generation systems, such as IS-2000, UMTS, HSXPA, 1xEV- DO, TD-CDMA and TD-SCDMA, to use CDMA as the access scheme. However, the issue with CDMA is that it suffers from poor spectral flexibility and computationally intensive time-domain equalization (high number of multiplications per second) for wideband channels. Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC- FDMA), Interleaved FDMA and Multi-carrier CDMA (MC-CDMA) are gaining more importance for the next generation systems. These are based on efficient FFT algorithms and frequency domain equalization, resulting in a lower number of multiplications per second. They also make it possible to control the bandwidth and form the spectrum in a flexible way. However, they require advanced dynamic channel allocation and traffic adaptive scheduling. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is used for the downlink. By contrast, Singel-carrier FDE is used for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus require energy-inefficient linear amplifiers. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved. The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMOenvironments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver. In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase- shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards. [edit]IPv6 support Main articles: Network layer, Internet protocol, and IPv6 Unlike 3G, which is based on two parallel infrastructures consisting of circuit switched and packet switched network nodes respectively, 4G will be based on packet switching only. This will requirelow-latency data transmission. By the time that 4G was deployed, the process of IPv4 address exhaustion was expected to be in its final stages. Therefore, in the context of 4G, IPv6 support is essential to support a large number of wireless-enabled devices. By increasing the number of IP addresses, IPv6 removes the need for network address translation (NAT), a method of sharing a limited number of addresses among a larger group of devices, although NAT will still be required to communicate with devices that are on existing IPv4 networks. As of June 2009, Verizon has posted specifications that require any 4G devices on its network to support IPv6.[26] [edit]Advanced antenna systems Main articles: MIMO and MU-MIMO The performance of radio communications depends on an antenna system, termed smart or intelligent antenna. Recently, multiple antenna technologies are emerging to achieve the goal of 4G systems such as high rate, high reliability, and long range communications. In the early 1990s, to cater for the growing data rate needs of data communication, many transmission schemes were proposed. One technology, spatial multiplexing, gained importance for its bandwidth conservation and power efficiency. Spatial multiplexing involves deploying multiple antennas at the transmitter and at the receiver. Independent streams can then be transmitted simultaneously from all the antennas. This technology, called MIMO (as a branch of intelligent antenna), multiplies the base data rate by (the smaller of) the number of transmit antennas or the number of receive antennas. Apart from this, the reliability in transmitting high speed data in the fading channel can be improved by using more antennas at the transmitter or at the receiver. This is called transmit or receive diversity. Both transmit/receive diversity and transmit spatial multiplexing are categorized into the space-time coding techniques, which does not necessarily require the channel knowledge at the transmitter. The other category is closed-loop multiple antenna technologies, which require channel knowledge at the transmitter. [edit]Open-wireless Architecture and Software- defined radio (SDR) One of the key technologies for 4G and beyond is called Open Wireless Architecture (OWA), supporting multiple wireless air interfaces in an open architecture platform. SDR is one form of open wireless architecture (OWA). Since 4G is a collection of wireless standards, the final form of a 4G device will constitute various standards. This can be efficiently realized using SDR technology, which is categorized to the area of the radio convergence. [edit]History of 4G and pre-4G technologies The 4G system was originally envisioned by the Defense Advanced Research Projects Agency (DARPA).[citation needed] The DARPA selected the distributed architecture and end-to-end Internet protocol (IP), and believed at an early stage in peer- to-peer networking in which every mobile device would be both a transceiver and a router for other devices in the network, eliminating the spoke-and-hub weakness of 2G and 3G cellular systems.[27] Since the 2.5G GPRS system, cellular systems have provided dual infrastructures: packet switched nodes for data services, and circuit switched nodes for voice calls. In 4G systems, the circuit-switched infrastructure is abandoned and only a packet- switched network is provided, while 2.5G and 3G systems require both packet-switched and circuit- switched network nodes, i.e. two infrastructures in parallel. This means that in 4G, traditional voice calls are replaced by IP telephony.

. In 2002, the strategic vision for 4G— which ITU designated as IMT-Advanced—was laid out. . In 2005, OFDMA transmission technology is chosen as candidate for the HSOPA downlink, later renamed 3GPP Long Term Evolution (LTE) air interface E-UTRA. . In November 2005, KT demonstrated mobile WiMAX service in Busan, South Korea.[28] . In April 2006, KT started the world's first commercial mobile WiMAX service in Seoul, South Korea.[29] . In mid-2006, Sprint Nextel announced that it would invest about US$5 billion in a WiMAX technology buildout over the next few years[30] ($5.76 billion in real terms[31]). Since that time Sprint has faced many setbacks, that have resulted in steep quarterly losses. On May 7, 2008, Sprint, Imagine, Google, Intel, Comcast, Brig ht House, and Time Warner announced a pooling of an average of 120 MHz of spectrum; Sprint merged its Xohm WiMAX division with Clearwire to form a company which will take the name "Clear". . In February 2007, the Japanese company NTT DoCoMo tested a 4G communication system prototype with 4x4 MIMO called VSF-OFCDM at 100 Mbit/s while moving, and 1 Gbit/s while stationary. NTT DoCoMo completed a trial in which they reached a maximum packet transmission rate of approximately 5 Gbit/s in the downlink with 12x12 MIMO using a 100 MHz frequency bandwidth while moving at 10 km/h,[32] and is planning on releasing the first commercial network in 2010. . In September 2007, NTT Docomo demonstrated e- UTRA data rates of 200 Mbit/s with power consumption below 100 mW during the test.[33] . In January 2008, a U.S. Federal Communications Commission (FCC) spectrum auction for the 700 MHz former analog TV frequencies began. As a result, the biggest share of the spectrum went to Verizon Wireless and the next biggest to AT&T.[34] Both of these companies have stated their intention of supporting LTE. . In January 2008, EU commissioner Viviane Reding suggested re-allocation of 500–800 MHz spectrum for wireless communication, including WiMAX.[35] . On 15 February 2008 - Skyworks Solutions released a front-end module for e-UTRAN.[36][37][38] . In 2008, ITU-R established the detailed performance requirements of IMT-Advanced, by issuing a Circular Letter calling for candidate Radio Access Technologies (RATs) for IMT-Advanced.[39] . In April 2008, just after receiving the circular letter, the 3GPP organized a workshop on IMT-Advanced where it was decided that LTE Advanced, an evolution of current LTE standard, will meet or even exceed IMT-Advanced requirements following the ITU-R agenda. . In April 2008, LG and Nortel demonstrated e-UTRA data rates of 50 Mbit/s while travelling at 110 km/h.[40] . On 12 November 2008, HTC announced the first WiMAX-enabled mobile phone, the Max 4G[41] . In December 2008, San Miguel Corporation, southeast Asia's largest food and beverage conglomerate, has signed a memorandum of understanding with Qatar Telecom QSC (Qtel) to build wireless broadband and mobile communications projects in the Philippines. The joint-venture formed wi-tribe Philippines, which offers 4G in the country.[42] Around the same time Globe Telecom rolled out the first WiMAX service in the Philippines. . On 3 March 2009, Lithuania's LRTC announcing the first operational "4G" mobile WiMAX network in Baltic states.[43] . In December 2009, Sprint began advertising "4G" service in selected cities in the United States, despite average download speeds of only 3– 6 Mbit/s with peak speeds of 10 Mbit/s (not available in all markets).[44] . On 14 December 2009, the first commercial LTE deployment was in the Scandinavian capitals Stockholm and Oslo by the Swedish- Finnish network operator TeliaSonera and its Norwegian brandname NetCom (Norway). TeliaSonera branded the network "4G". The modem devices on offer were manufactured by Samsung (dongle GT-B3710), and the network infrastructure created by Huawei (in Oslo) and Ericsson (in Stockholm). TeliaSonera plans to roll out nationwide LTE across Sweden, Norway and Finland.[45][46] TeliaSonera used spectral bandwidth of 10 MHz, and single-in-single-out, which should provide physical layer net bitrates of up to 50 Mbit/s downlink and 25 Mbit/s in the uplink. Introductory tests showed a TCP throughput of 42.8 Mbit/s downlink and 5.3 Mbit/s uplink in Stockholm.[47] . On 25 February 2010, Estonia's EMT opened LTE "4G" network working in test regime.[48] . On 4 June 2010, Sprint Nextel released the first WiMAX smartphone in the US, the HTC Evo 4G.[49] . In July 2010, Uzbekistan's MTS deployed LTE in Tashkent.[50] . On 25 August 2010, Latvia's LMT opened LTE "4G" network working in test regime 50% of territory. . On 6 December 2010, at the ITU World Radiocommunication Seminar 2010, the ITU stated that LTE, WiMax and similar "evolved 3G technologies" could be considered "4G".[2] . On 12 December 2010, VivaCell-MTS launches in Armenia 4G/LTE commercial test network with a live demo conducted in Yerevan.[51] . On 28 April 2011, Lithuania's Omnitel opened LTE "4G" network working in 5 biggest cities.[52] . In September 2011, All three Saudi telecom companies STC, Mobily and Zain announced that they will offer 4G LTE for high speed USB sticks for mobile computers, with further development for telephones by 2013.[53] . In 2011, Argentina´s Claro launch 4G HSPA+ network in the country. . In 2011, Thailand's Truemove-H launch 4G HSPA+ network with nation-wide availability. . On February 10, 2011, the Samsung Galaxy Indulge offered by MetroPCS is the first commercially available LTE smartphone[54][55] . On March 17, 2011, HTC ThunderBolt offered by Verizon in the U.S. was the second LTE smartphone to be sold commercially.[56][57] . On 31 January 2012, Thailand's AIS and its subsidiaries DPC under co-operative with CAT Telecom for 1800 MHz frequency band and TOT for 2300 MHz frequency band launch the first field trial LTE in Thailand by authorization from NBTC[58] . In February 2012, Ericsson demonstrated mobile- TV over LTE, utilizing the new eMBMS service (enhanced Multimedia Broadcast Multicast Service).[59] . On 10 April 2012, Bharti Airtel launched 4G [LTE] in Kolkata, first in India which resulted India to be one of the first countries in the world to deploy the cutting edge technology commercially.[60] . On 20 May 2012, Azerbaijan's biggest mobile operator Azercell launched 4G [LTE].[61] [edit]Deployment plans This section of the article is too long to read comfortably, and needs subsections. Please format the article according to the guidelines laid out in the Manual of Style. (May 2012) In May 2005, Digiweb, an Irish fixed and wireless broadband company, announced that they had received a mobile communications license from the Irish telecoms regulator ComReg. This service will be issued the mobile code 088 in Ireland and will be used for the provision of 4G mobile communications.[62][63] Digiweb launched a mobile broadband network using FLASH-OFDM technology at 872 MHz. On September 20, 2007, Verizon Wireless announced plans for a joint effort with the Vodafone Group to transition its networks to the 4G standard LTE. On December 9, 2008, Verizon Wireless announced their intentions to build and begin to roll out an LTE network by the end of 2009. Since then, Verizon Wireless has said that they will start their rollout by the end of 2010. On July 7, 2008, South Korea announced plans to spend 60 billion won, or US$58,000,000, on developing 4G and even 5G technologies, with the goal of having the highest mobile phone market share by 2012, and the hope of an international standard.[64] Telus and Bell Canada, the major Canadian cdmaOne and EV-DO carriers, have announced that they will be cooperating towards building a fourth generation (4G) LTE wireless broadband network in Canada. As a transitional measure, they are implementing 3G UMTS that went live in November 2009.[65] Sprint Nextel offers a 3G/4G connection plan, currently available in select cities in the United States.[44] It delivers rates up to 10 Mbit/s. Sprint has announced that they will launch a LTE network in early 2012.[66] In the United Kingdom and in Ireland, O2 UK and O2 Ireland (both subsidiaries of Telefónica Europe) are to use Slough as a guinea pig in testing the 4G network and has called upon Huawei to install LTE technology in six masts across the town to allow people to talk to each other via HD video conferencing and play PlayStation games while on the move.[67] On February 29, 2012, the first commercial 4G LTE service in the UK launched in Borough of Southwark, London.[68] Ofcom is in the process of auctioning off the UK-wide 4G spectrum. This will use the airspace made available following the country's analogue television signal switch off.[69] Verizon Wireless has announced that it plans to augment its CDMA2000-based EV-DO 3G network in the United States with LTE, and is supposed to complete a rollout of 175 cities by the end of 2011, two thirds of the US population by mid-2012, and cover the existing 3G network by the end of 2013.[70] AT&T, along with Verizon Wireless, has chosen to migrate toward LTE from 2G/GSM and 3G/HSPA by 2011.[71] Sprint Nextel has deployed WiMAX technology which it has labeled 4G as of October 2008. It is currently deploying to additional markets and is the first US carrier to offer a WiMAX phone.[72] The U.S. FCC is exploring the possibility of deployment and operation of a nationwide 4G public safety network which would allow first responders to seamlessly communicate between agencies and across geographies, regardless of devices. In June 2010 the FCC released a comprehensive white paper which indicates that the 10 MHz of dedicated spectrum currently allocated from the1700 MHz spectrum for public safety will provide adequate capacity and performance necessary for normal communications as well as serious emergency situations.[73] TeliaSonera started deploying LTE (branded "4G") in Stockholm and Oslo November 2009 (as seen above), and in several Swedish, Norwegian, and Finnish cities during 2010. In June 2010, Swedish television companies used 4G to broadcast live television from the Swedish Crown Princess' Royal Wedding.[74] Safaricom, a telecommunication company in East& Central Africa, began its setup of a 4G network in October 2010 after the now retired& Kenya Tourist Board Chairman, Michael Joseph, regarded their 3G network as a white elephant i.e. it failed to perform to expectations. Huawei was given the contract the network is set to go fully commercial by the end of Q1 of 2011 Telstra announced on 15 February 2011, that it intends to upgrade its current Next G network to 4G with Long Term Evolution (LTE) technology in the central business districts of all Australian capital cities and selected regional centers by the end of 2011.[75][when?] Sri Lanka Telecom Mobitel and Dialog Axiata announced that first time in South Asia Sri Lanka have successfully tested and demonstrated 4G technology on 6 May 2011(Sri Lanka Telecom Mobitel) and 7 May 2011(Dialog Axiata) and began the setup of their 4G Networks in Sri Lanka.[76][77] Mobitel was able to reach 96Mbit/s of speed while Dialog Axiata reached 128Mbit/s on their demonstration. In mid September 2011, [5] Mobily of Saudi Arabia, announced their 4G LTE networks to be ready after months of testing and evaluations. In December 2011, UAE's Etisalat announced commercial launch of 4G LTE services covering over 70% of country's urban areas.[citation needed] As of May, 2012 only few areas have been covered.[citation needed] In India on 10 April 2012, India's telecom company Bharti Airtel has launched India's first 4g services in Kolkata using TD-LTE technology.[78] It's only 14 months back before the official launching in Kolkata when a group consisting of China Mobile, Bharti Airtel and SoftBank Mobile came together, called GTI (Global TDLTE Initiative) in Barcelona and they signed the commitment towardsTD-LTE (Time-Division Long-Term Evolution) standards for the Asian region. On 27 April 2012, Brazil’s telecoms regulator Agencia Nacional de Telecomunicacoes (Anatel) announced that the 6 host cities for the 2013 Confederations Cup to be held there will be the first to have their networks upgraded to 4G.[79] On 21 June 2012, SFR will launch 4G in Marseille. It will be the first 4G commercial launch in France. [edit]Beyond 4G research Main article: 5G A major issue in 4G systems is to make the high bit rates available in a larger portion of the cell, especially to users in an exposed position in between several base stations. In current research, this issue is addressed by macro-diversity techniques, also known as group cooperative relay, and also by Beam- Division Multiple Access (BDMA).[80] Pervasive networks are an amorphous and at present entirely hypothetical concept where the user can be simultaneously connected to several wireless access technologies and can seamlessly move between them (See vertical handoff, IEEE 802.21). These access technologies can be Wi-Fi, UMTS, EDGE, or any other future access technology. Included in this concept is also smart-radio (also known as cognitive radio) technology to efficiently manage spectrum use and transmission power as well as the use of mesh routing protocols to create a pervasive network.