Ethernet was originally designed to operate over a heavy coaxial cable, and was later updated to also support a thinner, lighter, coaxial cable type. Both systems provided a network with excellent performance, but they utilized a bus topology which made changing a network a difficult proposition, and also left much to be desired in regard to reliability. Also, many buildings were already wired with twisted-pair wire which could support high speed networks. Installing a coaxial-based Ethernet into these buildings would mean they would have to be rewired. Therefore, a new network type known as 10 Base-T was introduced to increase reliability and allow the use of existing twisted-pair cable. 10 Base-T is the world's most widely deployed Local Area Networking technology.
10 Base-T utilizes Category 3 (or higher) Unshielded Twisted Pair (UTP) cable in a star topology. Each node on the network has its own cable run back to a common hub, and each of these cable runs may be up to 100 meters (330 feet) in length. Figure One shows a simple 10 Base-T network.
10 Base-T network
10 Base-T can also be wired in a tree topology, where one "main" hub is connected to other hubs, which are in turn connected to workstations. Please note that the depth of a 10 Base-T tree network is limited to one layer below the main hub. It is also possible to combine 10 Base-T with any combination of the other 10 Mbps Ethernet technologies in an infinite number of ways to meet nearly any requirement. Figure Two shows a combination of 10 Base-T and 10 Base-2.
10 Base-T and Thin Ethernet Combination
10 Base-T has various advantages and disadvantages which make it suitable for some applications and less suitable for others. Some of them are listed below:
10 Base-T uses two pairs of wires: one pair for transmission and the second pair for recieve. The physical connector used is an 8 position modular plug, commonly referred to as an RJ-45. All cables must be rated at a minimum of Category 3, and must be wired such that pins 1 & 2 are on one twisted pair and pins 3 & 6 are on a second pair. Common wiring standards which meet this requirement are EIA/TIA T568A and T568B.
There are two pinouts used: MDI for DTE devices (such as computers, printers, etc.) and MDI-X (hubs). Connecting an MDI port to an MDI-X port requires a straight through cable, and connecting either MDI to MDI or MDI-X to MDI-X requires a crossover cable. Pinouts of the MDI and MDI-X interfaces are shown in Table One.
10 Base-T Pinouts
There are several applications for crossover cables in 10 Base-T networks. The most common reason is to cascade hubs together in a tree topology. If both hubs have only MDI-X ports then a crossover cable is needed. Another application for a crossover cable is to connect two DTE devices together without a hub.
A standard 10 Base-T crossover cable wiring diagram is shown in Table Two.
|10 Base-T Crossover Cable|
|SIDE 1||WIRE COLOR||SIDE 2|
Crossover Cable Pinout