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Network design
overwhelmed by broadcast traffic than 10-Mbps links. Perhaps a worst-case example is the
scenario where Avaya IP Telephones are deployed on a large subnetwork that is running IPX or
other broadcast-intensive protocol, with broadcasts approaching 500 per second. Although the
performance of the IP Telephones and the voice quality can be satisfactory in this environment,
this type of deployment is strongly discouraged.
This section covers:
Ethernet switches
Speed and duplex
Ethernet switches
The following recommendations apply to Ethernet switches to optimize operation with Avaya
endpoints. Theses recommendations are meant to provide the simplest configuration by
removing unnecessary features.
Enable spanning tree fast start feature or disable spanning tree at the port level. The
Spanning Tree Protocol is a Layer 2 loop-avoidance protocol. When a device is first
connected (or reconnected) to a port that is running spanning tree, the port takes
approximately 50 seconds to cycle through the Listening, Learning, and Forwarding states.
This 50-second delay is neither necessary nor desired on ports that are connected to IP
endpoints. Instead, enable a fast start feature on these ports to put them into the
Forwarding state almost immediately. If this feature is not available, disabling spanning
tree on the port is an option that should be considered. Do not disable spanning tree on an
entire switch or VLAN.
Disable Cisco features. Cisco features that are not required by Avaya endpoints include
channeling, cdp, and inline power. These features are nonstandard mechanisms that are
relevant only to Cisco devices, and can sometimes interfere with Avaya devices. The
CatOS command set port host <mod/port> automatically disables channeling and
trunking, and enables portfast. Execute this command first, and then manually disable cdp
and Cisco inline power. Then manually enable 802.1Q trunking as necessary.
Properly configure 802.1Q trunking on Cisco switches. When trunking is required on a
Cisco CatOS switch that is connected to an Avaya IP Telephone, enable it for 802.1Q
encapsulation in the nonegotiate mode (set trunk <mod/port> nonegotiate
dot1q). This causes the port to become a plain 802.1Q trunk port with no Cisco
autonegotiation features. When trunking is not required, explicitly disable it, because the
default is to autonegotiate trunking.
Speed and duplex
One major issue with Ethernet connectivity is proper configuration of speed and duplex. A
significant amount of misunderstanding exists in the industry as a whole with regard to the
autonegotiation standard.
how speed and duplex settings are determined and typically configured. It is imperative that the
speed and duplex settings be configured properly.
284 Avaya Application Solutions IP Telephony Deployment Guide
Table 67: Speed/duplex matrix
on page 285 is a quick reference for
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