no audio on Jabber mobile when answering calls from 2N IP Verso

[ilmatte]

Hello Cisco Community,

I have a strange problem with a 2N IP Verso Intercom registered on a Cisco Unified Call Manager 12.5. I have configured the intercom to call a Hunt Pilot when someone pushes the button. If the call is answered by an IP phone (located in the same subnet as the intercom), everything is fine and the two parties can talk to each other.

However, if the call is answered from Jabber Mobile (Android/iPhone), no audio is estabilished between the two parties. 

The main difference between the two cases is that the RTP traffic in the second case is routed through Expressway, but I have no clues on how better investigate this problem. I'm pretty sure this thing worked until some weeks/month ago, so there's something that has recently changed in the configuration somewhere which blocks the audio stream.

Does anybody has some hint to troubleshoot this issue?

Thanks to anyone in advance.

[b.winter · Accepted solution]

Have you even thought about basic IP routing and FW issues?
Maybe it's just not allowed in your network, that packets flow between the 2N device and the Expressway, because this would be the path of media packets.
You can check the tcpdump of the Expressway-C with wireshark for RTP packets from and to the Expressways.
In your case, you should see outgoing packets to the 2N device, but no incoming packets from the 2N. If that's the case, then maybe a FW is blocking the traffic somewhere.

Basic troubleshooting: Starting with Layer 1 and going up the OSI Layers, and not the other way round

[ilmatte]

Thanks @b.winter , that's something I'm actually investigating. The problem is the network architecture is quite complex, plus I'm sort of a newbie to the Cisco Communication enviroment. I am awaiting a firewall check by the guy responsible for it at the moment. I will report if this will solve the issue.

Best regards,

[ilmatte]

I'm not sure though, that the problem is the firewall. I mean: calls between local IP phones and Jabber softphones registered through Expressway works flawlessly, therefore I think the Firewall should not distinguish a call between an IP phone and a softphone vs. a call between the 2N intercom and a softphone. The 2N is a standard SIP endpoint and communicates with other endpoints with a RTP stream using standard ports which are already configured on the firewall policies.

[b.winter]

Is the 2N in the same subnet as the IP Phones?
I wouldn't say, that the 2N is a standard SIP endpoint compared to the Cisco Phones. The media port of the Cisco phones are controlled by CUCM.
But not for the 2N.

So if the 2N device uses different media ports than the Cisco phones and there is a FW between the subnet of the 2N/ip phones and the Exp-C, then maybe the FW rule for the RTP range doesn't cover all the needed ports.

But again: You can check the TCP dump of the EXP-C and check for incoming RTP packets.
Maybe the 2N has also a built-in packet capture. Otherwise you have to capture the traffic on the switch-port

Then, if you see RTP packets being sent from the 2N, but not reaching Exp or vice-versa, something in between blocks or doesn't route the packets correctly.

There is nothing else you can check anyway.
The call signaling doesn't show you, where the media packets are lost...

[ilmatte]

Hello @b.winter ,

thanks for your support. Today I discovered that there was a misconfigured firewall, which was blocking the RTP traffic between the 2N intercom and EWC. The problem here is that, the intercom doesn't use the same UDP port range for RTP, as the Cisco IP phones do. Therefore I should configure the firewall accordingly.

Best regards,