Computer Ports
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Computer Ports In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. Physically, a port is a specialized outlet on a piece of equipment to which a plug or cable connects. Electronically, the several conductors making up the outlet provide a signal transfer between devices. The term "port" is derived from a Dutch word "poort" meaning gate, entrance or door. ETHERNET PORTS: Ethernet is a family of computer networking technologies for local area networks (LANs) commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies. Systems communicating over Ethernet divide a stream of data into individual packets called frames. Each frame contains source and destination addresses and error-checking data so that damaged data can be detected and re-transmitted. The standards define several wiring and signaling variants. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair and fiber optic links in conjunction with hubs or switches. Data rates were periodically increased from the original 10 megabits per second, to 100 gigabits per second. Since its commercial release, Ethernet has retained a good degree of compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols. HISTORY OF ETHERNET: Ethernet was developed at Xerox PARC between 1973 and 1974.[1][2] It was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation.[3] The idea was first documented in a memo that Metcalfe wrote on May 22, 1973.[1][4] In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker and Butler Lampson as inventors.[5] In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. TYPES OF CABLE USED TO CONNECT TO ETHERNET PORTS: 1) Ethernet over twisted pair: Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Other Ethernet cable standards employ coaxial cable or optical fiber. Early versions developed in the 1980s included StarLAN followed by 10BASE-T. By the 1990s, fast, inexpensive technologies began to emerge. Currently the most popular are 100BASE-TX (fast Ethernet) and 1000BASE-T (gigabit Ethernet), running at 100 Mbit/s and 1000 Mbit/s (1 Gbit/s), respectively. These standards all use 8P8C connectors.[note 1] Meanwhile higher-speed implementations generally support lower-speed standards inclusively; thus it is possible to mix different generations of equipment. Inclusive capability is designated 10/100 or 10/100/1000- for connections that support such combinations.[1]:123 The cables usually have four pairs of wires (though 10BASE-T and 100BASE-TX only require two of the pairs). The three standards support both full-duplex and half- duplex communication. 2) Category 5 cable (Cat 5): Category 5 cable (Cat 5) is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the twisted pair design and differential signaling for noise rejection. Category 5 has been superseded by the Category 5e (enhanced) specification. 3)Modular connectors: Modular connector is the name given to a family of electrical connectors originally used in telephone wiring and now used for many other purposes. Many applications that originally used a bulkier, more expensive connector have now migrated to modular connectors. Probably the most well known applications of modular connectors are for telephone jacks and for Ethernet jacks, both of which are nearly always modular connectors. Types of modular connectors: a) 4P4C: The 4P4C connector, is popularly, but incorrectly, called RJ22, RJ10, or RJ9. It is also commonly referred to as a "Handset Connector" because of the most popular usage for the connector.[5] It is the de facto industry standard for wired telephone handsets. It is used to provide connection from the base of the telephone to the handset.This handset connector is actually not a registered jack at all, since it was never intended to connect directly to the telephone service lines: RJ connects a phone to the service lines, while 4P4C connects two parts of a phone. Other RJ connector wiring standards are used by telephone companies. The 4P4C is only used for an end user application from the phone to the handset. b) 6P6C: The 6P2C, 6P4C, and 6P6C modular connectors are probably most well known for their use as RJ11, RJ14, and RJ25 registered jacks respectively. RJ11 is a physical interface often used for terminating telephone wires. It is probably the most familiar of the registered jacks, being used for single line POTS telephone jacks in most homes across the world. RJ14 is similar, but for two lines, and RJ25 is for three lines. RJ61 is a similar registered jack for four lines. The telephone line cord and its plug are more often a true RJ11 with only two conductors. Modular plugs are described as containing a number of potential contact "positions" and the actual number of contacts installed within these positions. RJ11, RJ14, and RJ25 all use the same six-position modular connector, thus are physically identical except for the different number of contacts (two, four and six respectively). c) 8P8C: The 8P8C (8 position 8 contact, also backronymed as 8 position 8 conductor) is a modular connector commonly used to terminate twisted pair and multiconductor flat cable. These connectors are commonly used for Ethernet over twisted pair, registered jacks and other telephone applications, RS-232 serial using the EIA/TIA 561 and Yost standards, and other applications involving unshielded twisted pair, shielded twisted pair, and multiconductor flat cable. Although commonly referred to as an "RJ45" in the context of Ethernet and category 5 cables, it is incorrect to refer to a generic 8P8C connector as an RJ45.[9][10][11][12] A telephone-system- standard RJ45 plug has a key which excludes insertion in an un-keyed 8P8C socket. [13] The registered jack (RJ) standard specifies a different mechanical interface and wiring scheme for an RJ45S from TIA/EIA-568-B which is often used for modular connectors used in Ethernet and telephone applications. 8P8C modular plugs and jacks look very similar to the plugs and jacks used for FCC's registered jack RJ45 variants, although the RJ45S is not compatible with 8P8C modular connectors. IEEE 1394 interface ports: The IEEE 1394 interface, developed in late 1980s and early 1990s by Apple as FireWire, is a serial bus interface standard for high-speed communications and isochronous real-time data transfer. The 1394 interface is comparable with USB and often those two technologies are considered together, though USB has more market share.[1] Apple first included FireWire in some of its 1999 models, and most Apple computers since the year 2000 have included FireWire ports, though, as of 2012, nothing beyond the 800 version (IEEE-1394b).[2] The interface is also known by the brand i.LINK (Sony), and Lynx (Texas Instruments). IEEE 1394 replaced parallel SCSI in many applications, because of lower implementation costs and a simplified, more adaptable cabling system. The 1394 standard also defines a backplane interface, though this is not as widely used. IEEE 1394 is the High-Definition Audio-Video Network Alliance (HANA) standard connection interface for A/V (audio/visual) component communication and control. FireWire is also available in wireless, fiber optic, and coaxial versions using the isochronous protocols. STANDARDS AND VERSIONS The previous standards and its three published amendments are now incorporated into a superseding standard, IEEE 1394-2008. The features individually added give a good history on the development path. FireWire 400 (IEEE 1394-1995) The original release of IEEE 1394-1995[ specified what is now known as FireWire 400. It can transfer data between devices at 100, 200, or 400 Mbit/s half-duplex data rates (the actual transfer rates are 98.304, 196.608, and 393.216 Mbit/s, i.e., 12.288, 24.576 and 49.152 megabytes per second respectively).These different transfer modes are commonly referred to as S100, S200, and S400. Cable length is limited to 4.5 metres (14.8 ft), although up to 16 cables can be daisy chained using active repeaters; external hubs, or internal hubs are often present in FireWire equipment. The S400 standard limits any configuration's maximum cable length to 72 metres (236 ft). The 6-conductor connector is commonly found on desktop computers, and can supply the connected device with power. The 6-conductor powered connector, now referred to as an alpha connector, adds power output to support external devices. Typically a device can pull about 7 to 8 watts from the port; however, the voltage varies significantly from different devices. Voltage is specified as unregulated and should nominally be about 25 volts (range 24 to 30). Apple's implementation on laptops is typically related to battery power and can be as low as 9 V. Improvements (IEEE 1394a-2000) An amendment, IEEE 1394a, was released in 2000,which clarified and improved the original specification. It added support for asynchronous streaming, quicker bus reconfiguration, packet concatenation, and a power-saving suspend mode. IEEE 1394a offers a couple of advantages over IEEE 1394. 1394a is capable of arbitration accelerations, allowing the bus to accelerate arbitration cycles to improve efficiency. It also allows for arbitrated short bus reset, in which a node can be added or dropped without causing a big drop in isochronous transmission.