hissing and static between internal / external calls in CUCM

[Gewy]

Good morning everyone.
I am reaching out to you today for some support as I have the following situation:
For some time now I have noticed that during my calls whether internal or external I hear hissing / static sounds, these sounds continue even though I have muted both microphones of the call. I have validated the following:
- Phones belong to the same Device Pool.
- Negotiation Codec: G722, G711
- I enabled the feature: "Silense Suppression" in Call Manager.
- Reset phones
- Test call with speakerphone / handset

Note: Call Manager Version: 12.5.1.10000-22 with ip phones: 3905 and 7821 registered with protocol SIP. Also, I have a Voice Gateway  model CISCO2921/K9 version 15.5(3)M4a.

However I have not been successful, I remain attentive to your kind comments of support.
Regards.

[Nithin Eluvathingal]

Are all the phones of 3905 and 7821 or only some particular ones showing this behaviour? I did not catch you mentioning that you upgraded the firmware. If the issue is on all the phones and there is a firmware upgrade option available, please try it.

[Elliot Dierksen]

Silence suppression means the end points try and determine when there is no audio to be sent, and don't send packets. I know, kind of obvious. The not obvious part is that human beings on a phone call (myself included) are quite put off by dead silence. They tend to think the call has been disconnected. In that case, the local device generates "comfort noise" so the humans don't think the call got disconnected. Sometimes the comfort noise is kind of obnoxious. I think that is what you are experiencing.