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List:       sip-implementors
Subject:    Re: [Sip-implementors] Question regarding PRACK
From:       "Bu, Wen Fei \(Leo\)" <wbu () lucent ! com>
Date:       2006-04-28 1:30:51
Message-ID: 2AC135F730C4A045BAE4F1C1CB83FD4B02FB83AE () exch03 ! qd ! lucent ! com
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-----Original Message-----
From: sip-implementors-bounces@cs.columbia.edu
[mailto:sip-implementors-bounces@cs.columbia.edu]On Behalf Of Atul kumar
Jha
Sent: Thursday, April 27, 2006 10:10 PM
To: sip-implementors@cs.columbia.edu
Subject: [Sip-implementors] Question regarding PRACK


Hi,

 

Consider this call flow:

 

Caller                  Callee 

     |   INVITE               |

     |----------------------->|

     |                        |

     |   183 SESSION PROGRESS |

     |<-----------------------|

     |    PRACK               |

     |----------------------->|           

     | 487 REQUEST TERMINATED |

     |<-----------------------|

     |   ACK                  |

     |----------------------->|

 

Caller is receiving 487 Request terminated for the INVITE request before
200 OK to the PRACK.

 

Q1. Should callee send 200 OK for PRACK before sending 487?
>>> No, per RFC3262, Page 5: The UAS MAY send a final response to the initial request
>>> before having received PRACKs for all unacknowledged reliable provisional responses,
>>> unless the final response is 2xx and any of the unacknowledged reliable provisional
>>> responses contained a session description.
>>> So, this is reasonable.

Q2. In case the above call-flow is ok, should caller terminate the PRACK
transaction or continue retransmitting PRACK until it gets 200  OK  for
it?
>>> I think it's better to retransmit PRACK until it gets 200 OK or transaction TIMEOUT.
>>> The transaction of PRACK is independent with the initial INVITE transaction, though 
>>> they are of the same dialog, which terminates when receiving 487.
>>> Also, per RFC3262, if the UAS does send a final response when reliable responses are
>>> still unacknowledged, it MUST be prepared to process PRACK request for those outstanding
>>> responses.
 

 

Please suggest on this.

 

Regards,

Atul

 

 

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