No voice on local (virtual PBX) calls between 7911G IP Phones

Unanswered Question
May 24th, 2009


I have the following issue. I have a small number of 7911G IP Phones connected to a 2811 router. When I try to place a call between the IP Phones (virtual PBX) they ring out but when the user tries to answer the phone the microphones are mute(d). If I try to place a call to the outside world (the router is a gateway to a PSTN network connection) everything works fine. Also if I place a call to a phone linked through an ATA 186 (I have a small number of those also) it also works properly. Could someone suggest on where to find the cause or kindly direct me to some documentation that would help me solve this issue? Thank you!

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Paolo Bevilacqua Sun, 05/24/2009 - 15:20

What do you mean the microphone is muted? Does the mute button lit? Or there is just no voice path ?

bsepsi Sun, 05/24/2009 - 15:26

What I mean is that when the handset is picked up and the user tries to speak into the microphone I can't hear anything on the other phone (where I'm located) and also he cannot hear me when I try to speak. Everything works fine if the other phone is not an IP Phone, that is if the call is not a local one or if the phone is connected using a ATA 186. It seems like there is no voice path.

Paolo Bevilacqua Sun, 05/24/2009 - 15:31

Are the phones local in the same VLAN? Are these SCCP phones configured under ephone and ephone-dn ?

bsepsi Sun, 05/24/2009 - 15:34

Yes they are SCCP phones configured using epone and ephone-dn. There is no VLAN defined because it's a small network only with a few users and it's main and only purpose is to act as a office telephony network.

bsepsi Sun, 05/24/2009 - 16:05

The IOS is IP Voice one with the following version "Cisco IOS Software, 2800 Software (C2800NM-IPVOICEK9-M), Version 12.4(22)T, RELEASE SOFTWARE (fc1)". I cannot give you the phone FW because they are not near me. I can get that information only in the morning (it's midnight here).

Paolo Bevilacqua Sun, 05/24/2009 - 16:11

You should be able to see that with "show ephone phone-load". I assume the phones are all connected to a switch, get DHCP from the router in a same subnet, etc.

bsepsi Sun, 05/24/2009 - 16:15

The phone FW reported by the show ephone phone-load is SCCP11.8-3-2S. Yes they are connected to a switch and get the DHCP from router in the same subnet.

Paolo Bevilacqua Sun, 05/24/2009 - 16:27

Your problem is very strange. I recommend you start upgrading to 12.4(22)T1. If that doesn't help you should look at upgrading phone FW as well.

bsepsi Sun, 05/24/2009 - 16:32

Ok. I will try that. Tnak you!

P.S. Couldn't be some RTP or some codec related issue?

Paolo Bevilacqua Sun, 05/24/2009 - 16:39

Evidently RTP is not being received correctly across 7911s. There is no evident reason for this to happen.


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