[SIPForum-discussion] sip prack

[Nitin Kapoor]

Hello Karthik,

The PRACK request plays the same role as ACK, but for provisional responses.


There is an important difference, however. PRACK is a normal SIP message,
like BYE. As such, its own reliability is ensured hop-by-hop through each
stateful proxy. Also like BYE, but unlike ACK, PRACK has its own response.
If this were not the case, the PRACK message could not traverse proxy
servers compliant to RFC 2543.

Along with that sip UA indicates support for this standard by
including a *"Supported:
100rel" or "Required: 100rel"* as a SIP header. The SIP headers claim to
support it or require it, but when you send them a non-100 1xx message, they
don't PRACK it.

Thanks,
Nitin Kapoor

On Thu, Dec 30, 2010 at 8:58 PM, karthik <karthik8989 at rediffmail.com> wrote:

> Hi ALL,
>
> Please help me understand this....
>
> 1.What is prack?
>
> 2.why is prack used?
>
> 3.What are the reasons for using prack?
>
> 4.What is the difference between prack , ack and 200 OK?
>
> Thanks,
> Karthik
>
>
>
>
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