Audio drops on LAN calls

[george630us]

We are having an issue where audio will drop for 3-5 seconds periodically during an IP phone to IP phone calls. The call will stay up, just a period of silence. We have 6920 phones and the 3300 controller.

What I have noticed is that if I change the switchport access vlan (not the voice vlan that the phones are using) to a less busy vlan that the drops do not occur. These drop can happen within the same switch, we do have QoS enabled.

I think these phone might use ARP as a keep alive an suspect they cannot keep up with the amount of traffic on the busier vlan.

Any thooughts?

 

[V3RTechNP]

Some things I would do to make a diagnostic :
- Enable Voice Quality Monitoring in 3300 and look at the stats of the problematic calls. Is there any packet loss, jitter, etc.? From which end?
- Wireshark with port mirroring or a hub/tap between the switch port and IP phone to see anything strange.
- Network monitoring tool like Cacti, Nagios, etc. to get bandwidth graphs of your switch uplinks. Is there a bottleneck somewhere?
- Making sure with Wireshark that packets are really tagged with the correct voice VLAN all the way between both IP phones -- maybe the voice packets are getting untagged somewhere and switch to data VLAN due to a bad switch configuration.

The untagged VLAN shouldn't matter once the phone has booted up and switched to voice VLAN. If there's a lack of bandwidth at the switch level, whatever untagged VLAN you have there should give the same problem. So it sounds like something isn't right with your voice tagging or QoS.

 

[Valamagules]

I had this issue once, and turns out switch port speed was set incorrectly as half duplex instead of FULL.
Worth the check

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