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Table 67: Speed/duplex matrix
Device 1
configuration
Autonegotiate
Autonegotiate
Autonegotiate
Autonegotiate
100/full
10/half
100/half
A duplex mismatch condition results in a state where one side perceives a high number of
collisions, while the other side does not. This results in packet loss. Although it degrades
performance in all cases, this level of packet loss might go unnoticed in a data network because
protocols such as TCP retransmit lost packets. In voice networks, however, this level of packet
loss is unacceptable. Voice quality rapidly degrades in one direction. When voice quality
problems are experienced, duplex mismatches are the first thing to look for.
VLANS
VLANS are an often-misunderstood concept. This section begins by defining VLANS, and then
addresses configurations that require the Avaya IP Telephone to connect to an Ethernet switch
port that is configured for multiple VLANs. The IP Telephone is on one VLAN, and a personal
computer that is connected to the telephone is on a separate VLAN. Four sets of configurations
are given: Avaya Cajun P330 v3.2.8 and later, Avaya Cajun P330 pre-3.2, Cisco CatOS, and
some Cisco IOS.
Device 2
Result
configuration
Autonegotiate
100/full expected and often achieved, but not
always stable. Suitable for user PC connections,
but not suitable for server connections or uplinks.
May be suitable for a single IP Telephony call,
such as with a Softphone. Not suitable for multiple
IP Telephony calls, such as through a MedPro
circuit pack.
100/half
100/half stable. Device 1 senses the speed, and
matches accordingly. Device 1 senses no duplex
negotiation, so it goes to half duplex.
10/half
10/half stable. Device 1 senses the speed and
matches accordingly. Device 1 senses no duplex
negotiation, so it goes to half duplex.
100/full
Device 1 goes to 100/half, resulting in a duplex
mismatch, which is undesirable. Device 1 senses
the speed, and matches accordingly. Device 1
senses no duplex negotiation, so it goes to half
duplex.
100/full
100/full stable. Typical configuration for server
connections and uplinks.
10/half
Stable at respective speed and duplex. Some
100/half
enterprises do this on user ports as a matter of
policy for various reasons.
LAN issues
Issue 3.4.1 June 2005
285
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