[SIPForum-discussion] Using UPDATE for call transfers

Richard dude at mr.net
Fri Jun 26 12:55:27 UTC 2009

Caller A (UAC) connects a caller B's via UAS which caller B has call
forwarded to Caller C.  The UAS sends a new INVITE to Caller A, Call A
replies with 100 Trying and 180 ringing (SDP profile), UAS replies with a
PRACK and 200 OK, Then Caller A sends another 180 ringing (SDP profile),
Then Caller A sends an UPDATE (SDP profile) changing the Media port, The UAS
then sends 504 Server timeout.

Shouldn't the UAC (Caller A) do a RE-INVITE instead of an UPDATE?  RFC 3311
section 5.1 recommends sending a re-INVITE instead of an UPDATE.

My question is should UAC conform to this standard or is it grey area as
it's "recommended?"

Much Thanks!

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