Audio drops on LAN calls

[dporod]

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?

[VinceWhirlwind]

In your situation I would do the following:
1/ Rule out it being just one switch causing this - does it happen "within the switch" on multiple switches?
2/ check the switch logs for events such as STP blocking events.
3/ do performance monitoring on this switch to see what traffic is being inputted to it.
 
Congestion usually manifests itself as random dropped packets and poor quality voice, not periods of complete silence. This sounds more like some other mechanism is interrupting all traffic.

[Dogbreath]

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.

Look at traffic graphs for the switchports with handsets on. If the switchport only has a handset on it, there should be a clear pattern of symmetric traffic. If there is way more RX than TX on a port with only a handset on, then there must be a lot of broadcast traffic.

[dporod]

In your situation I would do the following:
1/ Rule out it being just one switch causing this - does it happen "within the switch" on multiple switches?
2/ check the switch logs for events such as STP blocking events.
3/ do performance monitoring on this switch to see what traffic is being inputted to it.
 
Congestion usually manifests itself as random dropped packets and poor quality voice, not periods of complete silence. This sounds more like some other mechanism is interrupting all traffic.

It happens both within the switch and on multiple switches. STP looks fine. I've done packet captures on the switch, looks normal.

[Dogbreath]

You need a packet capture covering when the issue happens. Do you see a gap in the RTP when the issue happens?