| A system designed to achieve 100 Mbps access time on
Ethernet networks, which is 10 times the speed of standard Ethernet. The IEEE* amended the
802.3 specifications to include 100 BaseTX, 100 BaseT4 and 100 BaseFX. 100 BaseT is
configured in a star topology and therefore requires the use of a hub. Signals are
transmitted from a central hub directly over one cable segment to the NIC's. Fast
Ethernet makes use of the same CSMA/CD access method allowing multiple
devices to operate while avoiding transmission collisions. Although Fast Ethernet works at
10 times the speed of standard Ethernet, it also operates at over 10 times less the
maximum allowable network diameter - from 2500 meter to 210 meters over copper. There are two classes of repeaters (hubs) in 100 BaseT - Class I
and Class II. When using Class I, data should not pass
through more than one repeater and two 100 meter cable segments. Class I
has a latency of .7 or less microseconds. When using Class II, data
should not pass through more than two repeaters, two 100 meter cable segments and one 10
meter interrepeater link. Class II has a latency of .46 or less
microseconds (latency is the waiting time).
The same rules apply as for 10BaseT except as noted above.
The 100BaseT standard is made up of 3 versions:
100BASE TX is full-duplex capable in point
to point unshared applications because it uses 1 pair to receive and 1 pair to transmit.
Designed to run over 2 pairs of category 5 unshielded twisted pair cable
with RJ45 connectors and EIA/TIA 568B pinning. It can also be run on IBM type 1 sheilded
twisted pair (existing Token Ring wiring) with an impedence matching device and DB9
connectors or regular STP and DB9 connectors. Max segment length is 100m.
100BASE T4 designed to run over 4 pairs of
category 3, 4 or 5 UTP cable with RJ45 connectors and EIA/TIA 568B pinning. It can also be
run over STP. 1 pair is used to receive while 3 pairs are used to transmit,
however full-duplex operation does NOT work because specific pairs are not designated to
transmit or receive. Max segment length is 100m.
100BASE FX designed to run over 2 strands
of duplex multimode fiber optic cable. It's also full-duplex capable because it uses one
strand for receive and one for transmit. Maximum cable segment varies depending on the
cabling used. Singlemode (depending on the manufacturer) can exceed 10 km when
full-duplex. Multimode maximum length is 412 meters for half-duplex and 2 km ful-duplex.
Max length from station to repeater is 150 meters.
NOTE: For full-duplex operation on 100BASE TX or FX:
1) devices must support full-duplex
2) connection must be unshared end to end. |
