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(C) Herbert Haas
2005/03/11
100 Mbit Ethernet Overview
Fast Ethernet
100Base4T+
Signaling
Fast Ethernet
100BaseX
Signaling
100BaseTX100BaseFX
100BaseT4
(half duplex)
100VG-AnyLAN
"100BaseT"
HP and AT&T
invention for real time
applications
IEEE 802.3u
Signaling Schemes
IEEE 802.12
Demand Priority
The diagram above gives an overview of 100 Mbit/s Ethernet technologies,
which are differentiated into IEEE 802.3u and IEEE 802.12 standards. The IEEE
802.3u defines the widely used Fast Ethernet variants, most importantly those
utilizing the 100BaseX signaling scheme. The 100BaseX signaling consists of
several details, but basically it utilizes 4B5B block coding over only two pairs of
regular Cat 5 twisted pair cables or two strand 50/125 or 62.5/125-Fm multimode
fiber-optic cables.
100Base4T+ signaling has been specified to support 100 Mbit/s over Cat3 cables.
This mode allows half duplex operation only and uses a 8B6T code over 4 pairs
of wires; one pair for collision detection, three pairs for data transmission. One
unidirectional pair is used for sending only and two bi-directional pairs for both
sending and receiving.
The 100VG-AnyLAN technology had been created by HP and AT&T in 1992 to
support deterministic medium access for realtime applications. This technology
was standardized by the IEEE 802.12 working group. The access method is
called "demand priority". 100VG-AnyLAN supports voice grade cables (VG) but
requires special hub hardware. The 802.12 working group is no longer active.