Tuesday, September 20, 2005

Ethernet

Ethernet (this name comes from the physical concept of ether) is a frame-based computer networking technology for local area networks (LANs). It defines wiring and signaling for the physical layer, and frame formats and protocols for the media access control (MAC)/data link layer of the OSI model. Ethernet is mostly standardized as IEEEs 802.3. It has become the most widespread LAN technology in use during the 1990s to the present, and has largely replaced all other LAN standards such as token ring, FDDI, and ARCNET.
Varieties of EthernetOther than the framing types mentioned above, most of the other differences between Ethernet varieties have all been variations on speed and wiring. Therefore, in general, network protocol stack software will work identically on most of the following types.
The following sections provide a brief summary of all the official Ethernet media types. In addition to these official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling.
Many Ethernet cards and switch ports support multiple speeds, using auto-negotiation to set the speed and duplex for the best values supported by both connected devices. If auto-negotiation fails, a multiple speed device will sense the speed used by its partner, but will assume half-duplex. A 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T.
Some early varieties of EthernetXerox Ethernet -- the original, 3-Mbit/s Ethernet implementation, which in turn had two versions, Version 1 and Version 2, during its development. The version 2 framing format is still in common use. 10BROAD36 -- Obsolete. An early standard supporting Ethernet over longer distances. It utilized broadband modulation techniques similar to those employed in cable modem systems, and operated over coaxial cable. 1BASE5 -- Also known as StarLAN, was the first implementation of Ethernet on twisted pair wiring. It operated at 1 Mbit/s and was a commercial failure.
10 Mbit/s Ethernet10BASE5 (also called Thickwire or Yellow Cable) -- This is the original 10 Mbit/s implementation of Ethernet. The early IEEE standard uses a single 50-ohm coaxial cable of a type designated RG-8, of maximum length 500 metres. Transceivers could be connected by a so-called "vampire tap", which was attached by drilling into the cable to connect to the core and screen, or using N connectors at the end of a cable segment. An AUI cable then connected the transceiver to the Ethernet device. Largely obsolete, though due to its widespread deployment in the early days, some systems may still be in use. It requires precise termination at each end of the cable. 10BASE2 (also called Thinwire or Cheapernet) -- 50 ohm RG-58 coaxial cable, of maximum length 200 metres, connects machines together, each machine using a T-adaptor to connect to its NIC, which has a BNC connector. Requires termination at each end. For many years this was the dominant 10 Mbit/s Ethernet standard. StarLAN 10 -- First implementation of Ethernet on twisted pair wiring at 10 Mbit/s. Later evolved into 10BASE-T. 10BASE-T -- Runs over 4 wires (two twisted pairs) on a cat-3 or cat-5 cable up to 100 metres in length. A hub or switch sits in the middle and has a port for each node. FOIRL -- Fiber-optic inter-repeater link. The original standard for Ethernet over fiber. 10BASE-F (also called 10BASE-FX) -- A generic term for the family of 10 Mbit/s Ethernet standards using fiber optic cable: 10BASE-FL, 10BASE-FB and 10BASE-FP. Of these only 10BASE-FL is in widespread use. 10BASE-FL -- An updated version of the FOIRL standard. 10BASE-FB -- Intended for backbones connecting a number of hubs or switches, it is now obsolete. 10BASE-FP -- A passive star network that required no repeater, it was never implemented
Fast Ethernet (100 Mbit/s)100BASE-T -- A term for any of the three standards for 100 Mbit/s Ethernet over twisted pair cable up to 100 meters long. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2. 100BASE-TX -- Similar star-shaped configuration to 10BASE-T. It also uses two pairs, but requires cat-5 cable to achieve 100Mbit/s. 100BASE-T4 -- 100 Mbit/s Ethernet over cat-3 cabling (as used for 10BASE-T installations). Uses all four pairs in the cable. Now obsolete, as cat-5 cabling is the norm. Limited to half-duplex. 100BASE-T2 -- No products exist. 100 Mbit/s Ethernet over cat-3 cabling. Supports full-duplex, and uses only two pairs. It is functionally equivalent to 100BASE-TX, but supports old telephone cable (cat-3). 100BASE-FX -- 100 Mbit/s Ethernet over multimode fibre. Maximum length is 400 meters for half-duplex connections (to ensure collisions are detected) or 2 kilometers for full-duplex. 100Base-VG -- Championed by only HP, VG was the earliest in the market. It needed four pair of cat-3 cables. It is however questionable whether VG was really Ethernet.
Gigabit Ethernet1000BASE-T -- 1 Gbit/s over cat-5e or cat-6 copper cabling. 1000BASE-SX -- 1 Gbit/s over multi-mode fiber (up to 550 m). 1000BASE-LX -- 1 Gbit/s over multi-mode fiber (up to 550 m). Optimized for longer distances (up to 10 km) over single-mode fiber. 1000BASE-LH -- 1 Gbit/s over single-mode fiber (up to 100 km). A long-haul solution. 1000BASE-CX -- A short-haul solution (up to 25 m) for running 1 Gbit/s Ethernet over special copper cable. Predates 1000BASE-T, and now obsolete.
10 Gigabit EthernetThe new 10 gigabit Ethernet standard encompasses seven different media types for LAN, MAN and WAN. It is currently specified by a supplementary standard, IEEE 802.3ae, and will be incorporated into a future revision of the IEEE 802.3 standard.
10GBASE-CX4 -- designed to support short distances over copper cabling, it uses InfiniBand 4x connectors and CX4 cabling and allows a cable length of up to 15 m. 10GBASE-SR -- designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 m and 82 m depending on cable type. It also supports 300 m operation over a new 2000 MHz.km multi-mode fiber. 10GBASE-LX4 -- uses wavelength division multiplexing to support ranges of between 240 m and 300 m over deployed multi-mode cabling. Also supports 10 km over single-mode fiber. 10GBASE-LR and 10GBASE-ER -- these standards support 10 km and 40 km respectively over single-mode fiber. 10GBASE-SW, 10GBASE-LW and 10GBASE-EW. These varieties use the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment. They correspond at the physical layer to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respectively, and hence use the same types of fiber and support the same distances. (There is no WAN PHY standard corresponding to 10GBASE-LX4.) 10GBASE-T -- Uses unshielded twisted-pair wiring. 10GBASE-T should be ready by August 2006. 10 gigabit Ethernet is very new, and it remains to be seen which of the standards will gain commercial acceptance.

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