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188 Troubleshooting WLAN IP Telephony installations
– Ideally, there is no routing between any network devices used
for voice communication.
– If routing is necessary, keep it in the back-end, between the
SVP and PBX Call Server. Keep routing short and quick.
There are other access point parameters necessary for the proper
operation of voice communications. Often, these are not adjustable. By
specifying IP protocol 119 the following parameters are enabled on the
voice path in the access point:
•
Voice packet retry limit of three
If a voice packet is not ACKed, it is retried three times and then
dropped. This parameter must be enabled in the code to be able to
control the number of packet retries and limit them to three. There are
access points that identify IP protocol 119 (SpectraLink voice packets),
to limit packet retries to three and other access points simply identify
voice transmissions to limit retries.
•
Round Robin Queuing
During voice packet retry transmissions, the AP can also transmit
other voice packets in the queue. This ability prevents other wireless
telephones that use the AP from having their voice communications
held up while retries occur. This causes all other wireless telephones
to have poor audio while one wireless telephone is in a retry state.
These parameters can be invoked by specifying the voice profile or IP
protocol 119 < 10 ms latency. Disable the following parameters:
•
Dynamic Transmit Power at the Control (DTPC) for wireless clients
• AP Dynamic TX Power (or configure to On Demand Only)
•
AP Dynamic Channel Select (or configure to On Demand Only)
•
Intrusion Detection System (IDS) involvement
IDS causes the AP to go off channel and listen for other wireless
clients and APs. This causes degraded voice quality.
•
Load balancing at the AP for clients and network
• Interference detection and avoidance
• Coverage hole detection and correction
• Client Holdoff Time
• EAP or MAC Reauthentication interval
• TKIP MIC Failure Holdoff Time
Nortel Communication Server 1000
WLAN IP Telephony Installation and Commissioning
NN43001-504 03.04 Standard
23 September 2008
Copyright © 2004–2008 Nortel Networks
.