[OpenSIPS-Users] Problem with mediaproxy/engage_media_proxy with branches to same endpoint

[Henk Hesselink]

We're running up against a problem where engage_media_proxy seems to
handle multiple branches to the same endpoint incorrectly.  We've been
getting sporadic cases of no audio and we can now reproduce it.  This
is the simplest setup where it happens:

             R
             |
     A ----- P ----- D ----- T
                     |
                     M

A = Asterisk
P = proxy (OpenSIPS)
R = registrar (OpenSIPS)
D = dispatcher (OpenSIPS)
M = Mediaproxy
T = phone

What happens is:

1. the phone is unplugged (so can't unregister)
2. the phone is plugged in again and registers - there are now 2 entries
    in the location table until the old registration expires
3. a call is made from Asterisk to the phone
4. the lookup() in the proxy results in 2 branches
5. both INVITE branches are sent to the dispatcher
6. both result in a call to engage_media_proxy()
7. both INVITE branches are forwarded to the phone
8. the phone responds to one branch with
      a. "482 Loop Detected"
    and the other with
      b. "180 Ringing" and then "200 OK" with an SDP payload

If the dispatcher receives the 482 response before the 180/200 then the
SDP payload in the OK is for a different (new) mediaproxy session and we
get no audio.  What it looks like is happening is that the 482 response
causes the original mediaproxy session for all branches to terminate.

This doesn't seem correct behaviour to us, or is it correct and should
we be handling it in one of the configs?  We currently have a workaround
where we regularly flush old duplicate registrations, but it seems like
that shouldn't be necessary.

Regards,

Henk Hesselink