"James Sweet" wrote in message
news:zWCbf.12254$Ny6.9527@trnddc06...
CJT wrote:


http://www.cisco.com/en/US/tech/tk38...080091a86.html


Figure 7 of the cisco site shows all four pairs in use.


I can say with certainty from experience that 10bt uses only two of the
pairs, but 100bt and gigabit both use all four pairs. You have to make
sure you use both wires from the same pair for each set of signals too, if
you mix and match it doesn't work for 100 or gig, but 10 is slow enough
that it doesn't seem to matter for short runs.

INCORRECT, when the 100 Mb standard was being developed there were other
proposals that did call for all four (4) pairs to be used.
One argument 10 years ago -- that many installations (wiring closet to PC
desktop) were not compliant with EIA/TIA 568 (1992)-- and added undue cost
in rewiring these installations.

The referenced Cisco web page references the IEEE standards on which these
network solutions operate.

As Figure 7 shows, 1000BASE-T (1 Gb) works by using all four of the Category
5 pairs to achieve 1000 Mbps operation over the installed Category 5 copper
cabling. 1000 Mbps data rates are achieved by sending and receiving a 250
Mbps data stream over each of the four (4) pairs simultaneously (4 X 250
Mbps = 1 Gbps).

In contrast, 100BASE-TX uses two (2) pairs: one to transmit and one to
receive. Fast Ethernet on Copper (100BASE-TX) achieves 100 Mbps operation by
sending encoded symbols across the link at a symbol rate of 125 Mbaud.

Some in summary 10/100 Mb Ethernet solutions use 2 pairs and 1 Gb Ethernet
uses 4 pairs. All running on an EIA/TIA 568 compliant physical
infrastructure.

gb
IEEE member
Standards
Communications