Gigabit Ethernet over Copper :
Here is a summary of the standards time table for the Gigabit Ethernet
over copper standard, 1000BASE-T, the challenges inherent in transmitting
1,000 Mbps over four pairs of Category 5 unshielded twisted pair cabling
(UTP-5), and the use of simple DSP techniques to create robust systems.
Some people think that it is impossible to transmit 1,000 Mbps in a LAN
over standard UTP-5 copper cable over distances of 100 m. To determine
whether Gigabit Ethernet over copper is possible, we need to examine the
standards-making process, the technical challenges, the proposed
solutions, and whether these solutions are based on time-tested principles
and products.
Gigabit Ethernet over copper is called in the standards process
1000BASE-T, and it is currently under development by the IEEE 802.3ab Task
Force. This work represents the joint effort of more than eighty-five
individuals (working for about forty-four different organizations). This
joint effort means that the proposals are carefully scrutinized, analyzed,
debated, and simulated to ensure they can be built and can interoperate
with existing Ethernet standards. Many of the individuals bring extensive
experience to the process, as they are veterans of many other LAN
standards, including the pioneering work on Ethernet. The consensus in the
task force is that there is a solid draft for a standard, which can be
implemented soon.
Here is a short presentation which I prepared for an introduction to DSP section in ADSL and Gigabit Ethernet systems:
 | DSP.PPT |
The IEEE Standard 802.ab 1000BASE-T specifies the physical layer (PHY)
for Gigabit Ethernet over CAT-5 cabling systems.
Operating over the widely-deployed CAT-5 cabling systems currently used
for 100BASE-TX, 1000BASE-T provides a smooth way to increase the data rate
by ten times over 100BASE-TX. For every incoming data byte, the trellis
encoder outputs four PAM-5 symbols to four pairs of wires at 125MBaud/s.
The trellis code has an eight-state radix-4 trellis, it provides 6dB
coding gain for an ISI free channel. In practice, the gain could be less
than 6dB due to the ISI. Signals are transmitted on both directions on
each of the four wires, therefore, echo must be removed on each wire. In
addition, near-end cross-talk (NEXT) can also be removed in a way similar
to removal of echo cancellation.
©2003 Mehran Nekuii
