HI
I am sure this has been asked many times but I could not find a
definitive thread on how to resolve this. Moreover RFC 3261 section 14.2
is vague about resolving race conditions for Re-INVITEs. You could
directly skip over to offending section (in red) below for the issue in
question.
Here is the call flow
UA1 UA2
---INVITE (call leg#1)--- >
< -- 100 trying (call leg#1)--
< -- 180 ringing (call leg#1)--
< -- 200 OK (call leg#1)--
---ACK (call leg#1)--- >
<--- RTP established--- >
UA2 now initiates a new dialog with UA1 hybrid switch to call a 3rd
party to which the call should get bridged
UA1 UA2
< -- INVITE (call leg#2)--
---100 trying (call leg#2)--- >
---180 ringing (call leg#2)--- >
---200 OK (call leg#2)--- >
< -- ACK(call leg#2)--
UA2 now performs re-INVITE on call leg #1 and #2 to bridge RTP between
caller and transfer target on UA1 Switch.
UA1 UA2
< -- INVITE w/o SDP (call leg#2)--
---100 trying (call leg#2)--- >
---200 OK w/ SDP (call leg#2)--- >
< -- INVITE w/ SDP (call leg#1)--
---100 trying (call leg#1)--- >
---200 OK w/ SDP(call leg#1)--- >
< -- ACK w/ SDP(call leg#2)--
< -- ACK (call leg#1)--
Offending section
Now UA2 receives re-invite w/ SDP on call leg #1 from UA1. UA1 extracts
SDP from call leg #1 and sends a Re-INVITE to UA2 on call leg#2. At the
same time UA1 sends a re-invite on call leg#2 to UA2. These are part of
session refresh being triggered using re-invites.
UA1 UA2
-- INVITE w/ SDP (call leg#1)--- >
<-- INVITE w/ SDP (call leg#2)---
-- INVITE w/ SDP (call leg#2)--- >
<--491 request pending (call leg#2)---
-- 100 trying(call leg#2)--- >
-- 491 request pending(call leg#2)--- >
-- ACK(call leg#2)--- >
<-- ACK (call leg #2)---
Question is -
When a re-invite and 491 pending cross over happens on a dialog (call
dialog #2), how do both the UA resolve this. What retry timers are used
to resolve this and is there a draft available that addresses this
issue?
Thanks in advance
Dushyant
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