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Provisional response acknowledgement (PRACK
) is an IETF SIP extension that enables reliable transmission of provisional responses,Confirms that the client has received a final response to an INVITE.
PRACK is similar to ACK, but specific to the reliability of provisional responses.
The PRACK message is used in opening one-way media sessions before a call is
established and for quality of service (QoS) negotiation before completing an INVITE
transaction.
Each provisional response contains a sequence number that is stored in the RSeq header
field in the provisional response. The RSeq header is used to transmit the provisional
responses reliably. The PRACK messages contain an RAck header field, which indicates
the sequence number of the provisional response that is being acknowledged. This
header field is sent in a PRACK request to support reliable transmission of provisional
responses.
Posted by sagitraz
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