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Ethernet

The global standard for physically connecting computers together in a network. Almost every reference to "network," "network ready," "LAN," "LAN connection" or "network card" implies Ethernet....

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Definition: Ethernet

The global standard for physically connecting computers together in a network. Almost every reference to "network," "network ready," "LAN," "LAN connection" or "network card" implies Ethernet. Defined by the IEEE as the 802.3 standard, the Ethernet "access method" is used to connect computers in a company or home network as well as to connect a single computer to a cable modem or DSL modem for Internet access. See LAN.

All modern computers come with Ethernet. Older desktop machines can be retrofitted via USB or by plugging an Ethernet PCI card into an unused slot inside the case. Old laptops would need a USB socket.

Ethernet is built into new TVs, Blu-ray players and vitually all modern home theater equipment. It is also built into many home appliances as well.

Ethernet Is Wired - Wi-Fi Is Wireless
Ethernet uses cables to connect devices; however, the wireless counterpart to Ethernet is "Wi-Fi," and both wired and wireless operation is commonplace in companies as well as in the home. See Wi-Fi and wireless router.

Megabits Per Second: 10, 100, 1,000 and 10,000
A 10/100 Ethernet port supports two speeds: 10 Mbps and 100 Mbps. A 10/100/1000 port also includes Gigabit Ethernet at 1 Gbps (1,000 megabits). Modern devices have at least 10/100 and very likely 10/100/1000 connections. Devices negotiate to transmit at the highest speed possible. For high-speed backbones in metropolitan and wide area networks (MANs and WANs), 10 Gigabit Ethernet (10,000 megabits) is also used (see 10 Gigabit Ethernet).

Shared or Switched
Ethernet is wired in a star configuration with a hub or switch in the middle. Hubs, which predated switches, are shared media devices. All stations attached to the hub share the total bandwidth. Switches provide each sender and receiver pair with the full bandwidth and are significantly faster than hubs (see switched Ethernet). Like the client machines, Ethernet switches and hubs also support 10/100 and 10/100/1000 speeds.

Most Ethernets Use Twisted Pairs
Ethernet uses economical twisted pair cables and standard RJ-45 connectors (see cable categories). Sometimes, spare telephone wires in a building may be used, but often only at the lowest speed. To extend distances, fiber-optic cable is also used (see 100Base-T, Gigabit Ethernet and FOIRL). The first versions of Ethernet used coaxial cable (see 10Base5 and 10Base2).

Ethernet Frames
Ethernet transmits variable length frames from 72 to 1518 bytes in length, each containing a header with the addresses of the source and destination stations and a trailer that contains error correction data. Higher-level protocols, most notably IP, fragment long messages into the frame size required by the Ethernet network (see MTU).

Collision Detection
Ethernet uses the CSMA/CD technology to broadcast each frame onto the physical wire or fiber. All stations attached to the Ethernet are "listening," and the station with the matching destination address accepts the frame and checks for errors. Ethernet is a data link protocol (MAC layer protocol) and functions at layers 1 and 2 of the OSI model. See data link protocol.

History
Invented by Robert Metcalfe and David Boggs at Xerox PARC in 1973, Ethernet first ran at 2.94 Mbps. Metcalfe later joined Digital where he facilitated a joint venture between Digital, Intel and Xerox to collaborate further on Ethernet. Version 1 was finalized in 1980, and products shipped in the following year. In 1983, the IEEE approved the Ethernet 802.3 standard. See 100Base-T, Gigabit Ethernet, 10 Gigabit Ethernet and switched Ethernet.

 ETHERNET LIMITATIONS
                 Maximum         Max.
 Type            Segment length  Nodes
 TWISTED PAIR (star topology)
  10Base-T          328 ft/100 m    1
  100Base-T         328 ft/100 m    1
  1000Base-T        328 ft/100 m    1
 COAX (bus topology)
  10Base5 "thick"  1640 ft/500 m  100
  10Base2 "thin"    607 ft/185 m   30
 FIBER (star topology)
  FOIRL                .6 mi/1 km   1
  10Base-F            1.2 mi/2 km   1
  100Base-FX MM       1.2 mi/2 km   1
  100Base-FX SM         6 mi/10 km  1




Ethernet

Twisted Pair Ethernet
Ethernet uses twisted pair wiring with RJ-45 connectors between the network adapters in the PC and a central hub or switch.




Ethernet

Ethernet Switch
This Omnitron 10/100 switch has 16 ports and, like all Ethernet switches, automatically adjusts to the transmission rate of the line.





Ethernet

The Original Ethernet
The first Ethernet (10Base5) used a bus topology and a thick coaxial cable. Transceivers connect the network adapters to the cable via a vampire tap that \"bites\" into the coax.




Ethernet

Thin Ethernet
10Base2 Ethernet was a later variation of the original 10Base5. It used a thinner coaxial cable attached to each node using BNC T-connectors.





THIS DEFINITION IS FOR PERSONAL USE ONLY
All other reproduction is strictly prohibited without permission from the publisher.
© 1981-2010 The Computer Language Company Inc. All rights reserved.

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