[SIPForum-discussion] reliable 1xx

Himani Manglani himani.varandani at gmail.com
Thu Dec 6 16:35:21 UTC 2007

Prack is a reliablility mechanisum for provisional msgs(except 100 trying).
It works for 101-199 messsgaes. Its not just to secure SDP but also to stop
retransmission and ensure the msg delivery. Specially its important for
UAS  when INVITE transaction is taking time for sending response. In this
case UAS needs to either send provisional responses frequently or it
can send reliable provisional responses for extension of INVITE transaction


On Dec 6, 2007 4:39 AM, Anthony Orlando <avorlando at yahoo.com> wrote:

> Gurus,
>  I have a question regarding PRACKing of a
> provisional response.  My understanding has always
> been that you would only PRACK a 18x if it contains
> SDP.  The reason is  you want to ensure reliable
> delivery of the SDP.  Otherwise the 18x is not
> critical.
> Please feel free to comment and correct me if I am
> wrong.  Also is there a difference between 3gpp and
> IETF on this subject?  I am in an IMS environment.
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