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Some firewalls (in my case pfsense and m0n0wall) randomize outbound
ports that can cause problems for some ITSPs. That is, if the source port for the
REGISTER does not match the source port for the INVITE you may get an error
403.

The solution in pfsense is here:
http://doc.pfsense.org/index.php/Static_Port

Basically you configure manual
outbound NAT and specify the static port option.
(tip courtesy of Jonathan Petersen).

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If you are behind a NAT make sure that "Server Behind NAT" is checked in the _Internet Calling > NAT Traversal_ page.

Problem reporting

Please read this : Diagnosing Problems

Discuss problem on user list. Make sure there really is a problem and not just a misconfiguration. Detailed analysis will require a sipx-snapshot (wireshark traces do not suffice). Do NOT post excerpts of traces on the mailing list. They are not much use.

To take the snapshot :

1.  Set Set logging levels of sipxbridge to DEBUG if necessary. Configuration problems require only INFO level logging. Logging levels of sipXecs Proxy server to INFO, Loging level of sipXecs Registrar to INFO
2. Clean out the log directory.
3. Shut down the system.
4. For deep signaling issues (if asked for such information), edit _etc/sipxpbx/log4j.properties_. Add the line *log4j.category.org.sipfoundry.sipxbridge=trace*. This turns on detailed stack logging. Set the logging level to DEBUG on sipXbridge for stack logging to be enabled
5. Restart the system.
6. Run the problematic call flow.
7. See [oldxx:(!)missing link] for a GUI interface that allows you to take a snapshot. Alternatively you can use sipx-snapshot from the command line. Note that sipxsnapshot does not transmit any private data. It is absolutely required that this information be available to debug problems.
8. If the problem includes media issues such as one way speech, you would need to include a wireshark trace with your porblem report. You can filter the wireshark trace for RTP only. You can capture the trace using *tcpdump -n -nn -s 0 -i any -w sipx-tcpdump.cap* . You would also need to include a detailed trace for the media relay. For this edit _etc/sipxpbx/log4j.properties_. Add the line *log4j.logger.org.sipfoundry.sipxrelay=trace* (note: for version 4.0.4: *log4j.category.org.sipfoundry.sipxbridge.sipxrelay=trace*.) Save this and restart the media relay before running your test. It will generate a lot of logging information.
9. Open an issue and attach the snapshot, log files and pcap trace there or mail the list and ask for help on where to mail the snapshot.