[SIPForum-discussion] How should B2BUA maintain the SDP.

[Pavel Gavronsky]

Thank you, Keyur,
 
The reason for the SDP in our 180/183 from the TERMINATOR is to provide the RingBack tone from the remote party (early media).
For the case when the TERMINATOR doesn’t send the SDP in its 180/183, should the B2BUA use the "remembered" SDP value from the previous TERMINATOR leg or just pass the 180/183 (without SDP) unchanged to the ORIGINATOR?
 
________________________________________ 
Thank you in advance,
Pavel Gavronsky
 
From: Keyur Amin [mailto:fossil0681 at yahoo.com] 
Sent: Tuesday, February 14, 2012 6:18 PM
To: Pavel Gavronsky; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] How should B2BUA maintain the SDP.
 
SDP is required for the B2BUA from the terminator. It it doesnt get it 180/183, it must in 200 OK. The old SDP wont work because its a different end point. Unless the terminator is sending 183, you dont need SDP for 180. 
 
Thanks,
Keyur Amin
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From: Pavel Gavronsky <kamm555 at hotmail.com>
To: discussion at sipforum.org 
Sent: Monday, February 13, 2012 6:22 AM
Subject: [SIPForum-discussion] How should B2BUA maintain the SDP.
 
Hello, everyone,
 
Setup:
 
B2BUA – tandem SIP softswitch (tandem between softswitch_1 and softswitch_2)
ORIGINATOR: Subscriber connected to softswitch_1 
TERMINATOR1: Subscriber connected to softswitch_1
TERMINATOR2: Subscriber connected to softswitch_2
TERMINATOR3: Subscriber connected to softswitch_1
 
Scenario (only important messages shown):
Call comes from the ORIGINATOR and is routed to TERMINATOR1:
 
INVITE (to:TERM1, SDP=ORIG) -> B2BUA -> INVITE (to: TERM1, SDP=ORIG)
100 trying <- B2BUA <- 100 Trying
180 Ringing (SDP=TERM1) <- B2BUA <- 180 Ringing (SDP=TERM1)
_____________B2BUA -> Cancel (According to its internal logic B2BUA releases the TERM1 leg in order to make new call to TERM2)
_____________B2BUA -> INVITE (to:TERM2, SDP=ORIG) (According to its internal logic B2BUA makes new call to TERM2)
_____________B2BUA <- 100 Trying
180 Ringing (SDP=TERM1) <- B2BUA <- 180 Ringing (no SDP) ( ??? Is it correctly to provide the old SDP=TERM1 toward the ORIG in that case ???)
_____________B2BUA -> Cancel (According to its internal logic B2BUA releases the TERM2 leg in order to make new call to TERM3)
_____________B2BUA -> INVITE (to:TERM3, SDP=ORIG) (According to its internal logic B2BUA makes new call to TERM3)
_____________B2BUA <- 100 Trying
180 Ringing (SDP=TERM3) <- B2BUA <- 180 Ringing (SDP=TERM3) (Here the B2BUA correctly passes the SDP=TERM3)
 
 
Question:
If the 180/183 from the TERM leg does not include the SDP, should the B2BUA use the "remembered" old SDP value for the 180/183 toward ORIG leg? 
 
________________________________________ 
Thank you in advance,
Pavel Gavronsky
 

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