Sunday, May 2, 2010

Ethernet Standards

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The Ethernet standard you're most likely to be familiar with is 10Base-T, specified by IEEE 802.3. The "T" stands for twisted-pair cable, and the maximum length of a 10Base-T copper cable is 100 meters. The "10" refers to the 10 MegaBits Per Second (MBPS) capacity.

You may be asking "why twist the cable pairs?" Twisting pairs of wires inside the cable cuts down on the possibility of electromagnetic interference, whether that interference comes from another cable or an outside source - elevators are notorious for generating such interference.

In the previous illustrations, we looked at a network with a single coaxial cable and multiple hosts connected to that coax cable. That topology was used by the first Ethernet standards, 10Base5 and 10Base2.

The sole physical components were the Ethernet cards in the computers and coaxial cable, which is the topology we looked at in the previous example. The cable made up a bus that all the connected devices would use. This type of bus is referred to as a shared bus.

Ethernet is considered a logical bus topology.

The ending numbers in the terms "10Base5" and "10Base2" allegedly refer to the limit on the length of the cable, expressed in units of 100 meters. This is true for 10Base5; the limit on the cable length is 500 meters. It's not quite accurate for 10Base2, though; the limit on that cable is 185 meters, NOT 200 meters.

Fast Ethernet: -
Fast Ethernet is defined by IEEE 802.3u, and has a maximum capacity of 100 MBPS. Fast Ethernet copper cables also have a maximum cable length of 100 meters.

Gigabit Ethernet :-
Defined by IEEE 802.3z and 802.ab, Gigabit Ethernet has a maximum capacity of 1000 MBPS, also expressed as 1 GBPS (GigaBits Per Second). The maximum cable length is 100 meters here as well, but we cannot use a regular copper cable for Gigabit Ethernet.

Ethernet runs at 10 MBPS, defined by IEEE802.3, and its copper cable has maximum length of 100 meters. Variations include 10Base-T, 10Base-2, and 10Base-5, with the last two involving a shared cable bus.

Fast Ethernet runs at 100MBPS, is defined by IEEE 802.3u, and its copper cable has a maximum length of 100 meters.

Gigabit Ethernet runs at 1000MBPS (1 GBPS ), is defined by IEEE 802.3z, and also has a 100 meter cable length maximum - but it cannot use copper cabling.
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