Troubleshooting guide

Hardware
77
Distorted audio
only on NSU
Voice encoding is not
inverted.
For T1, enable invert for Voice encoding in link descriptor. For
CEPT or API, enable ADI invert for voice encoding. (This does not
apply to Embedded PRI.)
Broken Audio,
intermittent
Handsfree on the far
end.
Ensure that neither device is using handsfree. Some handsfree
phones only operate at half duplex.
Packet loss, jitter via
network.
1. Identify the speech path between the two end points, including
router, switch WAN in the audio stream.
2. The network administrator needs to apply QOS/TOS to minimize
jitter over slow speed interface (T1, Frame Relay, etc.), and give
voice traffic priority over data.
Limited bandwidth and
too many calls across
router, or combination
data and voice.
1. Limit the number of calls to remote subnets.
2. The network administrator needs to apply QOS/TOS to give
voice traffic priority over data.
Physical port error
(CRC, faulty cable,
duplex mismatch,
HUB).
1. Identify the speech path between the two end points, including
router, switch WAN in the audio stream.
2. Verify that there is no duplex mismatch in each port settings, or
faulty cable, or faulty port.
3. Make sure that the IP Phone is not plugged into a HUB.
Compression zone
enabled.
Compression will save bandwidth, but may cause noticeable
clipping. If not sure, disable compression to see if it makes a
difference.
Router's CPU is
exhausted or
congested.
Router may be running excessive filtering. The network
administrator may need to monitor the performance of the router.
Broken Audio,
intermittent
Layer 2 Switch ports
configured incorrectly.
1. In the Layer 2 Switch form of the System Administration Tool,
configure all L2 ports in the voice path with the same settings.
The recommended settings for the “Duplex Mode” field and the
“Flow Control” field is “Auto”.
2. If the network requires fixed settings, use the following:
- State - Enabled
- Speed - 100 Mb
- Duplex Mode - Full DX
- Flow Control - Enabled
- Voice VLAN - Tagged
3. If you change these fields to fixed settings, you must also set the
IP phones to use the fixed settings. You change the IP phone
settings through the Configuration menu. See “Access
Configuration Menu on Single-Mode IP Phones” on page 188.
4. In the Configuration menu, select Hardware Config? and then
select Modify Port Setting and modify the settings.
Table 20: Audio Quality Troubleshooting(continued)
Symptom Prossible Cause Corrective Action
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