Advanced Autonegotiation; Sample Problem Description; How Advanced Autonegotiation Works - 3Com 4007 Release Note

18 C 2: R
HAPTER ELEASE
Advanced
Autonegotiation
Sample Problem
Description
How Advanced
Autonegotiation
Works
H
IGHLIGHTS
Advanced Autonegotiation is an enhancement to the standard
autonegotiation feature that is defined in the IEEE 802.3u specification,
which addresses how two ends of a 10/100-TX Ethernet connection
become synchronized in speed and duplex mode. Due to limitations of
the specification, certain configurations produce duplex mismatches that
generate errors, reduce network performance, and may even "lock up"
an entire 802.3u-compliant switch. 3Com developed Advanced
Autonegotiation to overcome these limitations and correct duplex
mismatches on 10/100 links. In addition, although the 802.3u
specification does not apply to 100FX ports, Advanced Autonegotiation
also helps correct duplex mismatches on these links.
To illustrate the problem with the 802.3u specification:
Imagine a switch-to-switch connection (or switch-to-PC NIC connection)
where port A has standard autonegotiation enabled but port B does not
and instead is fixed at 100 Mbps and full duplex mode. The
auto-detection process in standard autonegotiation allows port A to
detect and match the speed of port B but port A cannot detect port B's
duplex mode and therefore port A defaults to half duplex mode per the
specification. Thus, a duplex mismatch exists and causes problems for the
link, switch, and network.
This problem affects any vendor's switch that complies with the
IEEE 802.3u specification. It is not unique to 3Com.
In this example, if port B had been fixed in half duplex mode, then a
duplex mismatch would not have occurred.
New to Software Release 3.0.5, Advanced Autonegotiation is related in
functionality to the Ethernet Port Monitoring feature that was introduced
in Software Release 3.0.
Port Monitoring monitors the error counters on specified ports and
provides notification via traps and messages on the management
interfaces. Port monitoring can also partition (temporarily disable) ports
that exceed a system error threshold.