OK you're right, I read the RfC and in fact a zero port means that the
stream is rejected. However the whole "negotiation" is still broken. If FS
rejects the incorrect G.722, OK, but what about all the other (perfectly
valid) codecs in the request (PCMA, PCMU)?

Because FS only rejects G.722, the call is doomed to fail, even though it
could work nicely if FS just selected one of the acceptable offers.

Roland