[OpenSIPS-Users] OpenSIPS as Teams SBC

[John Quick]

I agree completely with Ovidiu.
The Microsoft documentation says to use a FQDN in the Contact header, but
this is wrong when the SBC is acting as a SIP Proxy.
The blog post on the OpenSIPS website explains that actually the
Record-Route header needs the FQDN.
The one exception to this is the handling of OPTIONS pings - for these,
OpenSIPS is the end point so it must use a FQDN in Contact.

If you change the Contact header in call setup then you risk breaking the
path for sequential requests, such as ACK.
If ACK does not reach its destination, the call drops at one end after about
20 seconds - exactly what you are seeing.

I have not yet found a good way to capture TLS encoded SIP. In theory, you
can use sngrep with the -k option to identify the path to the private key
file.
It would be necessary to start sngrep first, then start (or restart)
OpenSIPS. However, this never works for me.
I had more success using the siptrace module to capture the packets to a DB
table. Presenting it as a sequence diagram may be possible using the
OpenSIPS Control Panel.
Wireshark also has the ability to capture, decode and present TLS encrypted
SIP.
Another option might be to mirror the traffic to Homer in HEP format and
then use Homer to create the sequence diagram.

John Quick
Smartvox Limited