For general SIP Proxy questions, try checking FAQ entry for SIP Problems.
Generally, problems with SIP fall into few categories:
- Timeouts
- Unauthorized or Disallowed Responses
- Dropped or Delayed Messages
There are several tools available to help diagnose SIP related problems. The biggest help when trying to track down issues is using a network capture tool (such as Wireshark) to monitor the flow of UDP traffic. Additionally, you can use the SIPp tool to generate simulated traffic (which can also send RTP data) in a controlled way.
UserAgent Timeouts
Timeouts happen when you try to contact the Sip Proxy, and you received no response. There are several possible problems which would cause this. The following list describes some minor issues and quick fix solutions:
Sip Proxy address (IP & Port) configured in the UserAgent is not correct - Correct Configuration
DNS Entry (when using a URL instead of IP) does not resolve to correct IP - Correct Configuration
The UserAgent is not using SIP (perhaps it is an IAX client?) - Use another client
For some reason, the SipProxy is not running - Try to start it up, pay attention to any errors if it fails again
Server is not running - Restart Server
Unauthorized / Disallowed
If during registration, the SipProxy server is sending back Unauthorized, check the return error message. Make sure that the User Agent is configured correctly (correct Sip Proxy, Realm, Username, Password, etc)
- If registration is successful, but calls fail, make sure that the User Account has sufficient funds to place the call. Alternatively, it could very well be that your system does not have funds in the external PSTN gateway you are using (which could be denying access). A was to figure out where this is coming from is looking at failure codes in the Call Detail Records (i.e. what gateway disallowed the call). If the record is not there, it is likely a mis-configured Billing Instance causing the call to go to the incorrect location (where it would not be authorized).
Dropped or Delayed Messages
Delayed Messages: Many of Sip Clients & Servers use roughly a 500ms retransmit rate for UDP messages. If, for whatever reason, the Sip Proxy is unable to respond quick enough, the User Agent will retransmit. Calamar SipProxy maintains a queue of incoming messages waiting to be processed. It marks each message with a time stamp, and will start to expire all messages older than a certain time. The reason for this is to prevent back logging the system with messages which will already have been resent. Normally, under ideal conditions, this will never happen and all messages will never be retransmitted since Calamar will respond before retransmission. However, if the server starts to reach its maximum capacity, there is a chance this will start to occur (at this point, you should check out the guide here for load balancing and/or system tweaks). Since Calamar is dropping messages, it will likely not send any old (delayed) messages back out to User Agent. If you are running an older version of Calamar, it is important to always stay upto date with the latest version, as an older release was prone to this condition (under abnormal circumstances).
Dropped Messages:
- Occasional Dropped messages is normal for UDP traffic. However, losses should be minimal on the same network. If not, Netstat command can generally be used to determine which system is dropping packets.