AS5400 HPX one way audio but two RTP flows

Unanswered Question
May 26th, 2009

Hi experts, I've a strange issue.

I've 2 AS5400 HPX gateway connected to PSTN network with E1 circuits.

I've many hundred of calls every day but a little percentage of theme presents one way audio.

Using wireshark I notice two RTP flows, one from AS5400 PSTN gateway to IP network and one in the opposite direction.

RTP stream from IP device to AS5400 is correct (in wireshark you can listen the audio), but the RTP from AS5400 doesn't contain voice (wireshark plays only silence).

In attached you can find configuration of my gateway and IOS version.

Do you have any suggestion?


I have this problem too.
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Nicholas Matthews Wed, 05/27/2009 - 04:38

There are some things you can do to troubleshoot this problem:

-Track down each of these calls while they are up and look for similarities. A common problem is that there is a bad b-channel and every call through that single b-channel has one way audio. This is normally a provider problem.

-Look at the actual payload data in the capture. If it is all 0's that means that something is dead. If there is still some 'noise' it's almost definitely a provider problem.

I would start by getting the callling/called numbers, the time, and which b-channel it was on and contacting your provider.


Daniele Giordano Thu, 05/28/2009 - 04:10

Your suggestion is very helpfull.

In wireshark trace the RTP payload is noise. I think like you in a provider's problem.

Do you know a way to test E1 b-channels?

In attached you can find n example of wireshark trace.


Daniele Giordano Sat, 10/06/2012 - 09:16

After many years I've changed the provider without fix the problem. So the problem is in the AS5400.

I've recently found this post on cisco support community about AS5400 one way audio problem:

... "no voice session-handle enable" is a hidden command to revert to behavior before CSCsg52095.

It  was introduced with CSCsr60092, and changes some flag behavior at the  DSP level in scenarios where packet generation is stopped and then  resumed.

The fix was verified with 5 people hitting the issue.

So  make sure you're running 12.4(15)T15, using the stock DSPware, and have  'no voice session-handle enable' and you should be good to go.

Execute "service internal" and after "no voice session-handle enable".

I've applied the hidden command and the problem seems fixed.

Can anyone give me more informations about this hidden command and related bugs?


aemcomcco Thu, 01/10/2013 - 05:36

We have some news:

- after many years I've changed the TDM provider without fix the problem

- the problem regards about 2% of both incoming and outgoing calls, so it is indipendent from direction of the call

- the audio issue is always in the call leg from TDM to IP side

- we observed this strange issue on all AS5400HPX gateway (3 different gateway with different IP address and bought in different period)

- a bidirectional RTP flow is always estabilished

- the problematic RTP flow from TDM to IP have always the same volume level: -24,4 dBm

- the wireshark audio trace shows only noise but if I increase the volume I can hear the voice (see original attachments)

- it happens on different DSP slot

So the problem is in the AS5400. Can be a configuration problem or an IOS - DSP bug?

Do you have any suggestions?

Best Regards.


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