Solved : Silent Call for some external calls - SIP

[eng.sultan.b]

Some users are complain that some time they faced a silent call (each party cannot hear anything) so they close the line and call again to make the call work.

But this issue occur suddenly so I can't capture the packet or do anything to fix the issue.

More info about this issue:

- Happens for different type of IP phones.

- Happens for outgoing and incoming calls.

- Happens in different time not only in peak hours.

So if anyone have any idea about this issue please let me know.

CUCM: 10.5.2.10000-5

VG: Cisco 3945 IOS Version 15.1(1r)T1

SIP Trunk between CUCM and VG also for serves provider.

[Aseem Anand]

Hi,

It could be an MTP/Xcoder issue. You need to check the MRGL defined under the trunk and make a note of all the Xcoders and MTP's in the MRGL. In case the MTP/Xcoder gets allocated the RTP will flow like:

IP phone >>>> RTP Traffic >>>>> MTP/Xcoder >>> Voice gateway

Make sure you the VG (3945) has connectivity with all the MTP/xcoders and if there is any firewall between the two then it should allow the RTP traffic between the two.

Aseem

(Please rate if useful)

[eng.sultan.b]

Hi Aseem,

Thank you for your prompt reply. Yes I checked all the resources and they are registered and listed in the MRGL under the trunk.

Also we are using only the resources for the VG and UCS and they are on the same subnet and no firewall between them.

And like I said, this issue happens suddenly not all the time. for example:

If IP phone A called an external mobile number he can't hear anything even the ringback tone also the other party can't hear anything. but if he close the line and call again the call works fine! so I don't think it's firewall issue am I right?

Even the service provider can't find any issue.

[Aseem Anand]

Hi Sultan,

It may or may not be a firewall issue but you can make sure if there is a firewall between the two then then complete RTP port range (16384-32768) is allowed by the firewall. Also, you need to setup captures by spanning the Voice VLAN and check if there are any routing issues.

Also, on the gateway you can setup you can setup a syslog server and enable debugs to see if the issue is with calls going through a particular channel/port. When you setup a syslog server, the output gets collected in a log file on the server running syslog. You can use Kiwi syslog.

Refer to the doc below:

https://supportforums.cisco.com/document/24661/how-configure-logging-cisco-ios

Aseem

[eng.sultan.b]

Solved

I removed the hardware resources from MRG and kept the software and that solved my issue.

My friend recommended me to do that but I don't know why this caused the issue!

Anyway thanks for your time Aseem and all.