Error in Trace SIP - Timeout of call server

Question

thank you for your help.

We have an application that generates calls to the customers, around 500 SIP calls simultaneous. Our app is only a customer of the SBC-Call Server. When the application start, the first calls are completed, but after that calls, we receive an timeout of the call server (50 seconds), for this reason we send a CANCEL in the signalization, because we do not receive any answer of the call server.

The trace of an call is:

0.80 We send an INVITE to call server 0.81 The call server returns 100 Trying. 50.79 We send a CANCEL (But 50 seconds later) why we do not receive any message.

What is the problem, the call server does not support the multiple sessions (500 calls)?

Answer 1

By sending the 100 Trying, the server indicates that it received the INVITE and it tries to route it. After the CANCEL, there is 487, meaning there was an active INVITE transaction. So without knowing what actually happened inside the SIP server, the assumption can be:

• the SIP server had no more resources to route the INVITE out
• INVITE was sent by the SIP server out, but there was no response from downstream to it

To really be able troubleshoot properly, you need to check the logs/activity of the SIP server and/or watch the SIP traffic on the network after the SIP server.