100BASE-TX 中的X代表。。。。。

        100Base-TX是一种规格，用于描述在5类非屏蔽双绞线上如何运行100Mbps快速以太网。5类UTP是当今在局域网中使用最普遍的一种电缆。
X的意思是e Xtended的缩写。扩展的意思。
100Base-TX

This is a current, March 2001, technology used in the widely usedtwisted pair form of networking cable architecture. The structure isEthernet; the 100 indicates 100 megabits per second transfer rate, orspeed of the net. The Base means a baseband network. The T indicates atwisted pair of wires. The X means extendedspecification in that two pair of wires is connected the transmit andanother two pair to the receive ports of the hub and or NICs.The wires can be shielded STP or unshielded UTP and it takes four pairsof twisted cable for one connection, eight wires. Each transmit pair istwisted with the other transmit pair and each receive pair is twistedwith the other receive pair. The more twists the better the performanceas a common rule. The connectors used are RJ-45s. This is also known asFastEthernetX. The maximum segment is published to be 100 metersalthough with quality CAT 5 or CAT 6 UTP or STP cable and goodconnections, it can often support distances of 150 meters. It is usedmost often as a higher performance version of 10Base-T and can co-existin the same network if the proper concentrators, bridges and switchesare present. Most network managers agree that the actual throughputdifference on a busy network is usually 1.5 to 2 times faster than10Base T, not the 10 times you would expect from the specifications.With no 10Base-T switches or sensing NICs on the network, thethroughput increase is somewhat higher but seldom exceeds 3 timesfaster than 10Base-T overall. This technology is excellent for speed inelectrically noisy environments.