Subject: [Sipping] PRACK vs. UPDATE in 3PCC

From: Lueken Joachim <[email-masked]>
Date: Thu, 16 Oct 2003 17:23:30 +0200

Hi,

In several flows of the 3PCC draft the sending of PRACK for one leg of the call depends on the reception of a message on the other leg of the call, e.g. in figure 8 the PRACK is sent to B once the 200 w/ answer2 is received from A.

Why did you not consider to use UPDATE here. Thus PRACK is no longer of end-to-end relevance and acknowledges reception of responses related to only one SIP call leg. I thought this was the intention behind PRACK. Although we introduce two additional message it looks much cleaner to me.

The flow in figure 8 would then look like this:

A                 Controller                  B        
|                      |                      |        
|(1) INVITE offer1     |                      |        
|no media              |                      |        
|<---------------------|                      |        
|                      |                      |        
|<ring>                |                      |        
|                      |                      |        
|<answer>              |                      |        
|                      |                      |        
|(2) 200 answer1       |                      |        
|no media              |                      |        
|--------------------->|                      |        
|(3) ACK               |                      |        
|<---------------------|                      |        
|                      |(4) INVITE no SDP     |        
|                      |--------------------->|        
|                      |                      |<ring>  
|                      |(5) 183 offer2        |        
|                      |<---------------------|        
|(6) INVITE offer2'    |(6a) PRACK            |        
|<---------------------|--------------------->|       
|(7) 200 answer2'      |(6c) 200 PRACK        |        
|--------------------->|<---------------------|        
|(8) ACK               |                      |        
|<---------------------|                      |        
|                      |(9) UPDATE answer2    |        
|                      |--------------------->|        
|                      |(10) 200 UPDATE       |        
|                      |<---------------------|        
|(11) RTP              |                      |        
|.............................................|        
|                      |                      |<answer>
|                      |(12) 200 OK           |        
|                      |<---------------------|        
|                      |(13) ACK              |        
|                      |--------------------->|        

Best regards / Mit freundlichen Gruessen
Joachim Lueken
 
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