Random One-Way Audio

[Brandon Pierce]

I have a strange issue that I have nailed down to one area of a customer's footprint for their UC infrastructure.  Basically, they get one-way audio on only a select few phones while others on the same VLAN and PRI do not exhibit these issues.  It's confusing as one-way audio is almost always network based but the problems follow the phone not the network if I bring it to another building on a different voice vlan.

Originally I thought it could be the PRI but since another building also uses that PRI and have no problems that kind of nixes that thought.  The network, well again, DHCP on another VLAN and the phone still has the same issues going out the same PRI.  If I change the PRI the phone works fine.  It's quite confusing and I had thought it might be a channel issue but since two entire buildings use the same PRI, that is not likely and the tests we did were on random channels since other calls were happening.

This isn't a very high call volume building the the issue does need resolved and I was hoping someone here could post some ideas since I am completely out of them.  I opened a TAC case and am waiting on them but would like some other insight from other people.  If I replace the phone having the problems, the issue will go away but then resurface again later down the road.  This issue has been happening for awhile and the recent upgrade for them from 7.0 to 9.1.2 hasn't resolved the issue either.

Summary Info:

• CUCM 9.1.2
• Cisco 2811 Voice Gateway MGCP Controlled
• Cisco 7940 Phones on SCCP
• Single voice subnet for one building
• One PRI for both buildings but only two or three phones exhibiting a problem in one of the buildings

Any insight here?  No network issues that I can think of since it's purely from IP Phone straight to the PRI and it doesn't have to traverse any other subnets.  No firewalls in play since the main internet router is elsewhere.  I was thinking originally UDP port issues but since it always happens for the same few phones.....

[Deven Gandhi]

Since you are suggesting this is not network issue, I am assuming you've done hard reset on the phones and let it grab newest firmware from TFTP server.  I would love to know how you resolve this issue with cisco TAC.  My past experience with one way audio were mostly network related.  

[Brandon Pierce]

I can't see how it is a network issue since all other phones on the network are fine and the problem follows the phone not the subnet.  It's interesting since I really want to put the blame on the PRI.  These phones have been all reset at one time or another and grabbed the latest firmware a few months ago when we did a major upgrade.  

[Scott Leport]

Is the one-way audio only present in outbound calls to the PRI or is it present in internal / intersite calls also?

If it's internal / intersite, can you run a test call between the two phones and pull the streaming statistics (click on the IP address of the phone in CUCM and navigate to Stream 1 under Streaming Statistics) and you'll see such things as Local and Remote IP address, negotiated codec etc and sender / receiver packets. You can do the same for the external call, but I would expect the Remote IP address to be displayed as your voice gateway, but it may be helpful to you and identify if the packet loss is being observed there.

Failing that, maybe this thread will be of some use since it seems loosely related to your issues:

https://supportforums.cisco.com/discussion/12444031/one-way-audio-mgcp-gateway

Good luck, I am interested in the outcome of this one.

[Ryan Huff]

First off I'll mention this, and this is really just a question because I don't see it mentioned, have you tried swapping out the handsets/cords on the impacted phones themselves? I'll be the first to admit that 7940's are tanks and never seem to die. That said, 7940's are ancient and it wouldn't be a surprise if hardware finally started to fail.

If you can try one of these 1-way audio calls and see Rx and Tx packets being exchanged on the phone, then try swapping handset/cords. Could be a failing / sporadic handset/cord issue .... shot in the dark.

• You mention that if you egress to a different PRI with these phones, you do establish two-way audio. If that is the case, is the PRI that you're switching to (that is working with two-way audio) also MGCP controlled? Is this PRI another daughter card in the same router or a separate router?

• Have you reset the MGCP gateway configuration in CCM and reset the MGCP configuration on the router? On the router, is the MGCP protocol being bound to the correct interface?

• Please attach the following output of the router:
• sh run | sec ccm-manager|sccp|mgcp

• Please attach the LAPD and control signal debug logs from the router from a 1-way audio call:
• debug isdn q921 and debug isdn q931

Thanks,

Ryan

[Brandon Pierce]

This ultimately was a foot in mouth issue and was routing.  Apparently, after reviewing the customers local gateway, they had two default routes pointing to the same direction.  One was via 0.0.0.0 0.0.0.0 fx/x and the other was 0.0.0.0 0.0.0.0 x.x.x.x.  Not sure why that would cause an issue, TAC was confused too.  My assumption is it was handling the route two different ways despite it going to the same place.