Internet
Objectives of this chapter – To introduce shortly history and presence of the Internet – To explain how is the Internet organized – To explain the principle of access technologies – To introduce some of well-known Internet services both traditional and advanced ones.
IRC - Lecture 3 - Internet 1 Internet Recapitulation of the previous chapter What we know about TCP/IP architecture? 1. TCP/IP architecture is the primary network architecture of worldwide Internet 2. TCP/IP protocol suite is structured into 4 layers – the network interface layer, the IP layer, the transport layer, the application layer. The data-link and physical layer is provided by other transmission technology, for example by Ethernet or Wi-Fi. 3. The key protocols of TCP/IP architecture are IP protocol belonging to the IP (or network) layer and TCP protocol belonging to the transport layer 4. The next protocol of the transport layer is UDP protocol, so applications may choose for transport of their messages or TCP that is reliable and slower or UDP that is faster but not completely reliable.
IRC - Lecture 3 - Internet 2 Internet
5. TCP/IP architecture uses IPv4 and IPv6 addressing scheme for unique identifications both networks and nodes. The network assigned with unique IP address within the Internet is the IP network. The node assigned with unique IP address within the IP network is the IP node. 6. IP address is a logical identifier which is assigned to the node or manually or automatically by DHCP service. 7. Larger LANs consist of number IP networks connected together by LAN IP routers. Routers determines the best path for IP data packets („datagrams“). Routers communicate one another using the routing protocols for sharing of routing information. 8. The collection of IP networks with common routing strategy is the autonomous system (AS). Each AS of Internet has its own unique identifier, which is AS number (ASN).
IRC - Lecture 3 - Internet 3 Internet
8. The users usually use for specification of network host domain names instead of its IP addresses. Domain name is an alphanumerical string. Each IP address should be associated with one or with more domain names. 9. The conversion of the domain name to the IP address is provided within distributed DNS (Domain Name System) through DNS servers. 11. In the term of DNS, the Internet (i.e. collection of IP networks) is a hierarchical virtual structure of DNS domains. – On the top of DNS structure is a root domain, next horizontal levels are top level domains and second level domains. – Top level domains (TLD) are or generic TLD (edu, gov….) or country TLD (cz, uk, sk, fr, tr, es ……) – Second level domains are mostly represented by LANs of enterprises, universities, etc. (for example mendelu.cz, microsoft.com….) – The lowest level comprises the domain names of single nodes
IRC - Lecture 3 - Internet 4 Internet
Implementation of TCP/IP architecture in the computer
IRC - Lecture 2 - Networking 5 Internet
• Each IP devices has a „private” („local“) or „public” („Internet“) IP address. • Local IP address must be unique address on that LAN („intranet“). • Internet IP address that is provided by the Internet Service Provider (ISP) must be unique address on the Internet. • The Internet Assigned Numbers Authority (IANA) established certain blocks of IPV4 addresses for the use of private (LAN) and public (Internet) addresses. The private IP addresses will fall within these specific ranges:
IANA-reserved private IPv4 network ranges Start End No. of addresses 24-bit block (/8 prefix, 1 × A) 10.0.0.0 10.255.255.255 16777216 20-bit block (/12 prefix, 16 × B) 172.16.0.0 172.31.255.255 1048576 16-bit block (/16 prefix, 256 × C) 192.168.0.0 192.168.255.255 65536
IRC - Lecture 3 - Internet 6 Internet
private addressing private addressing
public addressing
private addressing private addressing
• Communication between intranets with private addresses is not possible because the same addresses are used here (address collisions). • Communication is possible only by using the NAT method implemented on the border router. IRC - Lecture 3 - Internet 7 Internet
The principle of method Network Address Translation • Network address translation (NAT) is a method of remapping one IP address space (typically “private”) into another (typically “public”) and back by modifying network address information in Internet Protocol (IP) datagram packet headers while they are in transit across a traffic routing device.
Network Address Translation
private public
intranet
private public
IRC - Lecture 3 - Internet 8 Internet Virtual structure of DNS domains
Infrastructure TLD gTLD ccTLD IRC - Lecture 3 - Internet 9 Internet
Historical Generic TLDs Domain Intended use com Mainly for commercial entities, but unrestricted
Originally for organizations not clearly falling within org the other gTLDs, now unrestricted
Originally for network infrastructures, now net unrestricted Educational use, but now primarily for US third edu level colleges and universities
Governmental use, but now primarily for US gov governmental entities and agencies
mil Military use, but now primarily for US military only
IRC - Lecture 3 - Internet 10 Internet
How the Internet administration is organized • The Internet Assigned Numbers Authority (IANA) is an organization responsible for maintaining a collection of registries that are critical in ensuring global coordination of the DNS root zone, Autonomous systems, IP addressing, and other Internet protocol resources. • A regional Internet registry (RIR) is an organization that manages the allocation and registration of Internet number resources within a particular region of the world. It means, RIRs control assigning and distributing IP addresses and domain registrations. • Geographically, the Internet administration is divided into five regions: – AFRINIC – APNIC – ARIN – LACNIC
– RIPE NCC IRC - Lecture 3 - Internet 11 Internet RIRs • African Network Information Center (AFRINIC)[ for Africa • American Registry for Internet Numbers (ARIN) for the United States, Canada, several parts of the Caribbean region, and Antarctica. • Asia-Pacific Network Information Centre (APNIC) for Asia, Australia, New Zealand, and neighboring countries • Latin America and Caribbean Network Information Centre (LACNIC) for Latin America and parts of the Caribbean region • Réseaux IP Européens Network Coordination Centre (RIPE NCC) for Europe, Russia, the Middle East, and Central Asia
12 IRC - Lecture 3 - Internet Internet Internet Autonomous Systems • The Internet is administratively divided into Autonomous Systems. • ASs are under maintenance and control of a network operator or ISP (Internet service provider) company. • AS is a collection of networks under a common administration sharing a common routing strategy. • Autonomous system number (ASN) is a 16-bit decimal or 32–bit number that uniquely identifies the autonomous system. • Internet is interconnection of many autonomous systems. Each AS is connected to the Internet via an exterior router. • Exterior routers communicate one another by exterior routing protocols (EGP)
IRC - Lecture 2 - Networking 13 Internet Concept of Autonomous Systems
IRC - Lecture 2 - Networking 14 Internet - ISP Internet service provider (ISP) • ISP is company that provides a link to the Internet and other related services (such as Web site hosting and Mail service) for individual user or small enterprise’s LANs. • The larger ISPs are owners of high-speed links to the Internet backbone, therefore they are independent on the telecommunication providers which keep telecommunication lines. • Access networks of ISP (so called „the last mile“ networks) are connected together by Internet backbone. • ISP network operates usually as the Autonomous System (AS).
IRC - Lecture 3 - Internet 15 Internet ISP What is ISP „peering“ • ISP „Peering“ is the arrangement of communication (i.e. traffic exchange) ISPs. Larger ISPs with their own backbone networks agree to allow traffic from other large ISPs in exchange for traffic on their backbones. • Bilateral peering is an agreement between two parties. • Multilateral peering is an agreement between more than two parties. • NIX.CZ associates Internet Service Providers in the Czech Republic with the objective of interconnecting their networks. Most of ISPs operating within Czech Republic are members if NIX.CZ (Český Telecom, SkyNet, TISCALI, GiTy, Eurotel, CESNET, INTERNET CZ,…….) http://www.nix.cz/cs/networks
IRC - Lecture 3 - Internet 16 Internet - ISP How peering works
https://www.youtube.com/watch?v=i5oe63pOhLI
IRC - Lecture 3 - Internet 17 Internet ISP List of Internet change points • https://en.wikipedia.org/wiki/List_of_Internet_exchange_ points_by_size Peering centers - examples • France - https://www.franceix.net/en/ • Ghana - http://www.gixa.org.gh/members/ • Spain - https://www.de-cix.net/en/locations/spain/madrid • Portugal - http://www.datacentermap.com/ixp/gigapix.html • Mexico - http://www.datacentermap.com/ixp/mie.html • Kazakhstan, Russia - www.dataix.ru/en/ • ...... And many others
IRC - Lecture 3 - Internet 18 Internet - ISP ISP access to the Internet – Access networks is a type of telecommunications network which connects subscribers to their immediate service provider. – POP (point-of-presence) is an access point to the Internet. A POP necessarily has a unique Internet Protocol (IP) address – Modem (modulator/demodulator) is a communication device that converts digital data from computer into analog signals for conventional lines and vice versa. There are various types of modems designed for specific lines (DSL, TV cable, modems for wireless connection ….) IRC - Lecture 3 - Internet 19 Internet - ISP ISP Access Networks („last mile“) • An access network provides the end users access to Internet from a single home computer or from a very small home network or office network. The connection to the Internet may be or fixed (broadband) connection or dial-up connection (obsolete, replaced by broadband). • Some types of the broadband connections – Wireless connection – FWA (Fixed Wireless Access) or Wi-Fi access – radio waves are transmit from POP to user-end receiving device – ADSL (Asymmetric Digital Subscriber Line) – the transmission media is an existing telephone line that is shared by voice signal (a telephony) and data signal originated at user-end computer – CATV (Cable TV) - the transmission media is an existing TV cable that is shared by TV signal and data signal (from user-end computer) IRC - Lecture 3 - Internet 20 Internet - ISP ISP access to the Internet
Tier 1
Tier 2
Tier 3
IRC - Lecture 3 - Internet 21 Internet - ISP
Features of the access technologies • The access technologies implement an asymmetric load system. • Asymmetric system is that in which the data speed or quantity differs in one direction as compared with the other direction. • Asymmetrical data flow can make more efficient use of the available infrastructure than symmetrical data flow, in which the speed or quantity of data is the same in both directions, averaged over time. • In the term of asymmetric system we use the terms “upstream speed” /“uplink speed” (in the direction from the user-end to POP) and “downstream speed” /“downlink speed” (the direction towards the user-end). • The downstream speed is usually twice or more higher then upstream speed.
IRC - Lecture 3 - Internet 22 Internet - ISP
IRC - Lecture 3 - Internet 23 Internet
Principle of ADSL technology • ADSL modem and a telephone can use the common line simultaneously. • The modem uses two different frequency ranges (for “uplink” the lower one, for “downlink” the higher one), the telephone device transmits the voice in the range of voice frequencies, which are much more lower then modem’s “uplink” or “downlink” frequencies. • All frequencies share the same telephone link (frequency multiplexing and frequency de-multiplexing) • Splitter is device that provides frequency multiplexing/de-multiplexing on the user side and on the ISP side • DSLAM (Digital Subscriber Line Access Multiplexer) is a point of aggregation of users data channels located at ISP network head office.
24 IRC - Lecture 3 - Internet Internet -ISP ADSL Access to the Internet
IRC - Lecture 3 - Internet 25 Internet - ISP
• DSLAM (Digital Subsciber Line Access Multiplexer)
• ADSL modem
• ADSL splitter
IRC - Lecture 3 - Internet 26 Internet - ISP
IRC - Lecture 3 - Internet 27 Internet - ISP Principle of CATV (Cable TV) Access to Internet
• Subscribers connect to the system via a cable modem. • Once connected, subscribers obtain a continuous connection to the Internet via the cable network.
• The cable modem communicates with the CMTS (Cable Modem Termination System) in the head office. • The CMTS provides connections for thousands of cable modems over a network IRC - Lecture 3 - Internet 28 Internet - ISP
• CMTS (Cable Modem Termination System)
• CATV modem
• CATV Set top box
IRC - Lecture 3 - Internet 29 Internet - ISP Principle of Wireless Access Networks • An alternative to copper- or cable-based high-speed access ISP AP • Systems utilize a small microwave antenna that is attached to a radio system at the customer premises • The CPE (Customer Premises Equipment) is pointed back to the ISPs AP (Access Point ) - typically a tall building or radio tower • Both point-to-point and point-to-multipoint systems, operating in licensed as well as unlicensed bands (Wi-Fi) are available
IRC - Lecture 3 - Internet 30 Internet - ISP FWA (Fixed Wireless Access) and WiFi (Wireless Local area network)
FWA
WiFi
IRC - Lecture 3 - Internet 31 Internet - ISP
Data Communication Service in Mobile Networks • Mobile networks provide both voice and data transmission • What is „Mobile Internet“ – the access to Internet (to WWW system) from a handheld device (smartphone …) • The mobile network can distribute data to Internet nodes by means of specific mobile technologies, for example UMTS 3G (Universal Mobile Telecommunications System), HSDPA (High-Speed Downlink Packet Access) • Generation (G) of mobile technology - a set of standards used for mobile devices and mobile telecommunication services and networks
IRC - Lecture 3 - Internet 32 Internet - ISP
Mobile technologies generations • GPRS 2.5 G – packet switching (similar to IP service) – the client pays for an amount of transferred data • EDGE 2.75G – the same principle as GPRS – higher data rate • UMTS/HSDPA 3G – the newer service, the faster data transmission • LTE 4G (Long term Evolution) – the newest technology (available in limited geographic areas, but telecommunications providers have been actively expanding their LTE services)
IRC - Lecture 3 - Internet 33 Internet • What is “internet” – in general wide area network formed of many local area networks using TCP/IP protocol suite. • What is “Internet” (sometimes called „Net“) – international collection of many wide area networks and local area networks. Internet provides file and data transfer, together with electronic mail functions and many other services for many millions users around the world. • INTERNET usage statistics http://www.internetworldstats.com/stats.htm The primary network architecture of the Internet is TCP/IP.
IRC - Lecture 3 - Internet 34 Internet Short History of Internet • Internet was developed from the network named ARPANET which was designed in 1969 as a military project. The aim of ARPANET – „The network could continue to function even if parts of it were destroyed in the event of a military attack or any other disaster“. • During several next years, ARPANET connected many other networks of other institutions supporting the development of ARPANET. The IP protocol was adopted as an official network protocol – „Internet was born“. • In 1986, the U.S.A. National Science Foundation initiated the development of the NSFNET providing a backbone communication service for Internet. IRC - Lecture 3 - Internet 35 Internet
• The original ARPANET was shut down. • By the early 1990s, as commercial networks began to build their own backbone infrastructures and their own routing mechanisms and NSFNET was shut down. • The origin purely academic Internet became the Internet mainly commercial. • How can user gain the access to the Internet services (mail service, Web…) – within Enterprise’s or University’s LAN – by means of ISP (Internet Service Provider) or IAP (Internet Access Provider)
IRC - Lecture 3 - Internet 36 Internet Internet is the global information system Internet is „Network of Networks“ The most popular Internet services: – Internet electronic mail service – Remote access to file systems and file transfer service – Remote session service – Internet Web system – Social networking service – Peer-to-peer interactive communication service (ICQ, Skype..) – Internet video service – Internet audio service – E-commerce, e-learning, e-government ….
IRC - Lecture 3 - Internet 37 Internet services The main pillars of Internet • TCP (Transmission Control Protocol) - for the transfer data streams between communicating applications. • IP (Internet Protocol) - for addressing of Internet nodes and for routing of datagrams between communicating nodes • DNS (Domain Name System) - for translation of domain names used in the application programs to the IP addresses used by TCP/IP protocols. • URL (Universal Resource Locater) - a way of addressing documents and other resources on the World Wide Web (WWW).
URL uses the DNS system to identify the machine where documents reside. For example: http://www.mendelu.cz/pef tells the Web browser to look for an HTML document at IP address "195.178.72.10", in the directory "pef".
IRC - Lecture 3 - Internet 38 Internet services
• The URL contains the name of the protocol required to access the resource, a domain name that identifies a specific computer on the Internet, and a pathname (hierarchical description of a file location) on the computer. • On the WWW which uses the HTTP (Hypertext Transfer Protocol), an example of a URL is: http://www.ietf.org/rfc/rfc2396.txt • A URL for a file meant to be downloaded would require that the "ftp" protocol be specified like this one ftp://www.somecompany.com/whitepapers/widgets.ps • A URL for a mail service requested for to send message to the user specific address is mailto:[email protected]
IRC - Lecture 3 - Internet 39 Internet services • The most of Internet services is based on the principle client/server • 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 fulfils the request • The client/server model has become one of the central ideas of network computing • In the Internet, the client/server model provides a convenient way to interconnect programs that are distributed across different locations • The „client side“ is usually implemented in a program running on the user´s PC, the „server side“ is implemented in a program running on a common enterprise computer (usually called „the server“) • Typically, multiple client programs share the services of a common server program
IRC - Lecture 3 - Internet 40 Internet services The key client-server services available on the Internet • FTP (File Transfer Protocol) or SFTP (Secure FTP) protocols for moving files across the Internet. • Email - Electronic Mail. A set of protocols (POP, IMAP, SMTP, MIME) used for exchanging electronic mail messages. A Listserv is a mailing list that enables the members of the list to send messages to the entire list by simply sending an email to the List Server, which then distributes the message to all members of the list. • Remote access to the host machine. A command line system that allows a person on a computer anywhere on the Internet, anywhere in the world, to become directly connected (i.e. log in) to a computer anywhere else on the Internet. • WEB system. A client/server system for transfer of hypertext documents across the Internet. The system uses most commonly HTTP (HyperText Transport Protocol).
IRC - Lecture 3 - Internet 41 Internet - services
• The different way of communications is the peer-to-peer principle • Peer-to-peer is a communications model in which each party has the same capabilities and either party can initiate a communication session. • Both sides of peer-to-peer communication model are implemented in the similar programs running on remote computers • The typical Internet services which are based on the peer-to- peer model – Instant messaging ICQ (I seek you) – Video chat Skype
IRC - Lecture 3 - Internet 42 Internet services
FTP - File Transfer Protocol • FTP is a protocol for moving files (downloading and uploading) across the Internet. • FTP protocol is the simple way to exchange files between computers on the Internet, i.e. between local file system and remote file system. • FTP protocol enables user to download, delete, move or copy files or directories in two-way between the client’s and server’s file systems.
IRC - Lecture 3 - Internet 43 Internet services FTP implementation • Protocol FTP is implemented in the client program (FTP client) and in the server program (FTP server). • The FTP client program is usually running on the user’s PC, FTP server program run on the server (for example WinSCP) • User needs to log on the server, it means, that user has created an user account on FTP server at first
IRC - Lecture 3 - Internet 44 Internet services • What is it “FTP anonymous server” - anonymous FTP server enables anyone to download files from appropriately configured FTP server. This allows users without accounts to access files by entering the username “anonymous” or “ftp”, along with their email address as a password. • Administrator of FTP anonymous server need to be careful to use it only for files meant for public consumption Try to connect the anonymous FTP server via web browser (ftp://ftp.fi.muni.cz/) or by means of WinSCP (set protocol FTP, port 21)
IRC - Lecture 3 - Internet 45 Internet services Internet remote session • A user being at the terminal communicates with a host server by „shell“. Shell is program which operates between the user and the operating system, often to try and make the operating system more friendly or easier to use. • A user being at the remote computer can communicate with a host server as if he was at terminal. That remote session is enabled by protocol TELNET. • Protocol TELNET creates a virtual communication channel connecting the user’s computer and the host server, which transmits the characters that user types on the keyboard.
IRC - Lecture 3 - Internet 46 Internet services • Host server’s responses go through the virtual channel too, and are displayed on the user computer’s monitor. • Protocol TELNET is implemented in the client program “telnet”. • Server TELNET interacts with an application, acting as a proxy terminal handler so that remote terminal appears as local to the application • Client TELNET interacts with the terminal I/O module to communicate with a local terminal; it converts the characteristics of real terminals to the network standard and vice versa.
IRC - Lecture 3 - Internet 47 Internet services Principle of Remote terminal session
Telnet client
Applications: telnet, TeraTerm, putty … Applications: telnetd, sshd …
IRC - Lecture 3 - Internet 48 Internet services • Secure Shell (ssh/SSH) is an alternative way of the remote session. – It provides the secure communication channel between a host server and a user’s computer. All data transmitted through that channel are encrypted with agreed cipher key, so they are protected against unauthorized wiretapping. – The examples of programs implementing the secure remote terminal: • Putty • TeraTerm
IRC - Lecture 3 - Internet 49 Internet services
The Internet Electronic Mail The oldest and the most popular Internet service. The most important logical elements of the Internet mail system are: • Mail User Agent (MUA) - The client program utilized by the user to send and receive mail. Reading and writing messages may be done in this program or in a separate editor (e.g. word-processor). • Mail Transfer Agent (MTA) - A mail server program, which enables email transfers from one machine to another. MTAs do not actually deliver mail themselves. They prepare messages (e.g. by insuring that their envelopes are acceptable to the receiving server) and call a Mail Delivery Agent to physically transport the messages.
50 IRC - Lecture 3 - Internet Internet services
• Mail Delivery Agent (MDA) - A program that the MTA uses to put messages into a recipient's mailbox or to transport mail to another MTA. • Mail Retrieval Agent (MRA) - A program or service that fetches messages from a mailbox on a remote server and passes them to MUA. Typically used for dial-up internet mail.
IRC - Lecture 3 - Internet 51 Internet services Internet Mail protocols SMTP, POP3, IMAP4, MIME The Simple Mail Transfer Protocol (SMTP) provides the basic electronic mail facility. It provides a mechanism for transferring mail messages between separate hosts from client to server as well as from server to another server. It uses TCP protocol for the transfer of SMTP messages between the MTA module on the side of a sender and the MTA module on the side of recipient.
IRC - Lecture 3 - Internet 52 Internet services
• The Post Office Protocol (POP3) allows server-based mail to be downloaded, but has extremely limited remote mailbox management functions (basically limited to retaining or deleting the messages held on the remote server). POP is preferred by many ISPs because it is simpler to configure and administer than IMAP. • The Internet Message Access Protocol (IMAP) is a complex and powerful protocol, which allows to access and manipulate server-based mail from any location, from multiple mailboxes, etc. IMAP offers huge opportunities to exploit email as an e-commerce tool.
IRC - Lecture 3 - Internet 53 Internet services
IRC - Lecture 3 - Internet 54 Internet services Format of a mail message
55 IRC - Lecture 3 - Internet Internet services
Format of the electronic address The generic Internet e-mail address has a form: user@mailserver The part before @ (commercial at) represents the mail user’s username (i.e. user’s login name) at that mail server and may be substituted with the user’s full name or nickname after particular configuration setting on the mail server. For example: [email protected] [email protected]
IRC - Lecture 3 - Internet 56 Internet services The MIME specification • SMTP has traditionally been limited to the delivery of simple text messages. In recent years, there has been demand for the electronic mail to accommodate various types of data, including voice, images, and video clips. • The MIME specification was evolved to satisfy that requirement • MIME (Multipurpose Internet Mail Extension) is implemented in the mail applications (MIME is built in the MUA and MTA modules)
IRC - Lecture 3 - Internet 57 Internet services The MIME capability • The message body is extended with non-text content that is attached to the text message. • Files may be in various binary formats such as the image, sound and video format or it may be programs, HTML documents, MS Word documents etc. • MIME expands the message header with next fields that supply information about message body
IRC - Lecture 3 - Internet 58 Internet services The Internet Web system • A technical definition of the World Wide Web is: all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP) – The Web enables access to various services (e-mail, remote sessions, files transfer…) since almost every protocol type available on the Internet (includes SMTP, FTP or TELNET) is accessible on the Web. – An access to the Internet service is specified by means of URL: • http://whatis.com/cgi-bin/comments.pl • ftp://www.somecompany.com/whitepapers/widgets.ps • mailto:[email protected]
IRC - Lecture 3 - Internet 59 Internet services The origin and principle of the Web • In March 1989Tim Berners-Lee of the European Particle Physics Laboratory proposed the project as a means to better communicate research ideas among members of the remote organization. The Web uses individual pages, usually combined to make up Web sites. Web pages are written in HTML that tells the Web browser how to display the page and its elements. Web pages are stored in the Web servers and their copies are sent on demand to Web browsers. Web browsers perform the content of Web pages to users.
IRC - Lecture 3 - Internet 60 Internet services Key concepts of the Web – Protocol HTTP on the client/server communication model – Hypertext Markup Language HTML – Uniform Resource Locator URL – Common Gateway Interface CGI • HTTP (Hypertext Transfer Protocol) is the protocol used to transmit and receive data over the World Wide Web. • When you type a URL into your Web browser (which implements the HTPP client side), you are actually sending an HTTP request to a Web server (which implements the HTTP server side) for a page of information (that's why URLs begin with "http://"). • HTTP server (Web server) send a requested document in its response .
IRC - Lecture 3 - Internet 61 Internet services Principle of the communication within the Web system
IRC - Lecture 3 - Internet 62 Internet services • HTML (Hypertext Markup Language) - is the set of "markup" symbols or codes inserted in a text file intended for display on a World Wide Web browser. The markup tells the Web browser how to display a Web page's words and images for the user. The individual markup codes are referred to as elements (called tags). • Hypertext is a user interface paradigm for displaying documents. A document contains automated cross- references to other documents called hyperlinks. Selecting a hyperlink causes the computer to display the linked document within a very short period of time. • A document can be static (prepared and stored in advance) or dynamically generated (in response to user input) by means of CGI Common Gateway Interface).
IRC - Lecture 3 - Internet 63 Internet services • Web server is a program that, using the client/server model and the HTTP, serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). – Every computer on the Internet that contains a Web site must have a Web server program. – The most popular Web servers are Apache (a Web server for both 32- bit Windows and UNIX-based operating systems) and Microsoft's Internet Information Server (IIS). • Web browser is an application program that provides a way to look at and interact with all the information on the World Wide Web. – Web browser runs in the graphical user interface. – Many variations of Web browser for every type of operating system are available. The most popular is Microsoft’s Internet Explorer and Netscape Navigator. The other are Opera, Mozilla Firefox, Google Chrome, etc. IRC - Lecture 3 - Internet 64 Internet services • The common gateway interface (CGI) is a standard way for a Web server to pass a Web client's request to an application program and to receive data back to forward to the user. CGI is part of the HTTP protocol. • Principle of CGI – When the client requests a Web page (for example, by clicking on a highlighted word or entering a Web site address), the server sends back the requested page. However, when a user fills out a form on a Web page and sends it in, the input usually needs to be processed. – The Web server typically passes the form information to a small application program that processes the data and may send back a confirmation message.
IRC - Lecture 3 - Internet 65 Internet services • Searching services on the Web – deals with navigation through the Web space. The amount of information resources on the Web is continuously increasing, so it is very difficult for user to find the relevant ones. The Web searcher interact with a user which enters the keywords determining the subject of his interest. The Web searches seek in their databases and then generate the list of the links to wanted information. The servers use for their work the CGI interface. They are two ways for generating of database: a subject catalog and a search engine. • List of search engines • Examples Google - search engine http://www.google.com Webcrawler - search engine http://www.webcrawler.com/ Yahoo! - subject catalog + search engine http://www.yahoo.com Seznam - subject catalog + search engine http://www.seznam.cz
IRC - Lecture 3 - Internet 66 Internet services • Web technologies is a collection of means and tools which create the client/server application environment similar to Internet’s WWW system. Those technologies may be used in the many solutions, for example at e-government, e-learning, e-commerce, etc. • The basic components are: – Web server with CGI – Web client – Database server (SQL, Oracle…) • The CGI is created with the programming tools, such as: Java, Perl, PHP, JavaScript, ActiveX, XML etc.
IRC - Lecture 3 - Internet 67 Internet services • Web client (or Web browser or HTTP client) offers very convenient working environment for users. That is why it is became de facto standard for client-side solutions. • Web technologies are employed in the most today’s distributed applications (i.e. simple application modules run on the separate systems connected together through the network). • The example of that solution can be an enterprise’s information system running at enterprise’s intranet.
IRC - Lecture 3 - Internet 68 Internet services
69 IRC - Lecture 3 - Internet Internet services The Internet services offering individual or group communications • Non-interactive – E-mail discussion group - great variety of topics is covered by LISTSERVs, which are the programs, that provide the message from one subscriber is sent to other subscribers. – USENET Newsgroups - a global electronic bulletin board system in which millions of computer users exchange information on a vast range of topics. http://www.usenet.com/ • Interactive – ICQ https://icq.com/ – Skype https://www.skype.com/ – Videoconferencing (list of best videoconferencing SW http://www.pcmag.com/article2/0,2817,2388678,00.asp) • Social media enabling the social interaction among people in which they create, share or exchange information and ideas in virtual communities and networks – YouTube, Facebook, Twitter …….
IRC - Lecture 3 - Internet 70 Internet services ICQ - I seek you • The ICQ idea is to provide people around the world with the most complete means to communicate better • Both communicating parties must have downloaded the ICQ program and have received a user identification number ICQ#. • The download and registration procedure are simple and enable you to send messages directly to partners' desktops. • The most popular method of communication on ICQ is instant messaging, enabling us to send a message that immediately pops up on an online contact's screen.
IRC - Lecture 3 - Internet 71 Internet services
Internet voice services • IP telephony refers to communications services — voice, fax, and/or voice-messaging applications — that are transported via the Internet, rather than the public switched telephone network (PSTN). • The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and compression/translation of the signal into Internet protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end.
IRC - Lecture 3 - Internet 72 Internet services • Skype is a software that allows you to make calls from your computer. Talk for as long as you like without worrying about the cost or the distance. – Free Skype-to-Skype calls • Make video calls • Send cheap text messages • Easy conference calling
– SkypeOut allows Skype users to call traditional telephone numbers, including mobile telephones, for a fee.
IRC - Lecture 3 - Internet 73 Internet services • Videoconferencing allows for multiply users a real-time collaboration. Videoconferencing programs include the audio and video components in addition to the interactive chat program. The example of programs which provide the videoconferencing are, CUseeMe, GoToMeeting and other. • The usual collaboration tools are: – audio (conduct a conversation on the Web) – video (view member’s audience) – file transfer (send files back and forth among participants) – chat (type in real time) – whiteboard (draw, mark up, and save images on a shared window or board) – document/application sharing (view and use a program on another's desktop machine) – collaborative Web browsing (visit Web pages together)
IRC - Lecture 3 - Internet 74 Internet services
Videoconferencing
IRC - Lecture 3 - Internet 75 Internet services Videoconferencing
IRC - Lecture 3 - Internet 76 Internet services
Social Networks • Network of social interactions and personal relationships. • Network of individuals (such as friends, acquaintances, and coworkers) connected by interpersonal relationships. • Online service or site through which people create and maintain interpersonal relationships. • Dedicated website or other application which enables users to communicate with each other by posting information, comments, messages, images, etc.
IRC - Lecture 3 - Internet 77 Internet services Social Networks
Facebook 2,010,000,000 YouTube 1,500,000,000 Instagram 700,000,000 Twitter 328,000,000
IRC - Lecture 3 - Internet 78 Internet - Summary
Conclusion • Internet is the public global communication network. • It provides many variable services, the number of which is growing • The traditional services are e-mail service, file transfer, remote terminal and web system • Nowadays, the most attractive for users are services based on the real-time multimedia data streaming, for example the videoconferencing, IP TV or IP telephony.
79 Internet - Summary Answer following questions: 1.What are the basic principles of the Internet? 2.What are the main services of the Internet? 3.Describe the Electronic Mail System. 4.Describe the principle of the Remote Session (TELNET, SSH) and the File Transfer Service (FTP, SFTP). 5.Describe Web System include the functionality of the CGI. 6.What are the possibilities for an interactive communication within the Internet? 7.What are the ISP companies? What is the autonomous system (AS)? What is the peering? 8.Describe in brief technologies for access to Internet (i.e. access technologies). 9.Describe in brief mobile technologies for the access to Internet services.
IRC - Lecture 3 - Internet 80 Internet
• Are there any questions?
• Thanks for your attention
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