[SIPForum-discussion] CSeq count in call scenarios using PRACK and UPDATE Methods

Smitha Harish smithah at TechMahindra.com
Wed Feb 14 09:37:23 UTC 2007

Hi all,

I have a query on use of reliable Provisional Responses using the PRACK

In the call flow shown below between a UAC and UAS, if CSeq count is 2
in PRACK from UAC and CSeq is 1 in ACK from UAC, If a BYE gets initiated
from UAC itself, What count shall it hold in its Cseq? 2 (Base on INVITE
Cseq count) or 3(Based on PRACK Cseq count). Kindly clarify?



If an UPDATE is sent by the UAC before a 200 OK response for the INVITE
has been received in order to modify the session parameters in the
pending session, what is the CSeq count? Does it get incremented by 1 at
the UAC. If so does it take PRACK Cseq count as its previous count or
INVITE Cseq as its previous count?Kindly clarify?


Thanks in anticipation,




Tech Mahindra, formerly Mahindra-British Telecom.

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