[SIPForum-discussion] Query regarding Require and Supported

Abhishek Mishra abhishek.mishra at globallogic.com
Tue Aug 21 09:39:05 UTC 2007

Hi Chandan,

Reliability of Provisional Responses:

This is actually required if you need to send the provisional resopnses
reliably. In SIP, is UDP is used as the transport protocol, then the
provisional response transmission becomes unreliable. This is because
provisional resposes are not re-transmitted.

Actual requirement of reliability comes from PSTN<==>SIP interworking.
In PSTN network, provisional responses (like ACM) are always transmitted
reliably. So, if SIP is used as a bridge between long distance call,
then to ensure that all the messages (including provisional responses)
are transmitted reliably, this RFC is used.

Relibility of final responses is taken care by SIP using


On Tue, 2007-08-21 at 13:48, chandan kumar anjani wrote:
> Hi,
> In Require and Supported header does the 100rel means 100%
> reliablility is expected 
> or it is that all 1XX should be reliable.
> Bye
> Anjani
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