[SIPForum-discussion] Magic Cookie....

[Donald Lee]

Per RFC3261:
 8.1.1.7 Via
......
   The branch parameter value MUST be unique across space and time for
   all requests sent by the UA.  The exceptions to this rule are CANCEL
   and ACK for non-2xx responses.  As discussed below, a CANCEL request
   will have the same value of the branch parameter as the request it
   cancels.  As discussed in Section 17.1.1.3, an ACK for a non-2xx
   response will also have the same branch ID as the INVITE whose
   response it acknowledges.

      The uniqueness property of the branch ID parameter, to facilitate
      its use as a transaction ID, was not part of RFC 2543.

   *The branch ID inserted by an element compliant with this
   specification MUST always begin with the characters "z9hG4bK*".  These
   7 characters are used as a magic cookie (7 is deemed sufficient to
   ensure that an older RFC 2543 implementation would not pick such a
   value), so that servers receiving the request can determine that the
   branch ID was constructed in the fashion described by this
   specification (that is, globally unique).  Beyond this requirement,
   the precise format of the branch token is implementation-defined.
......
So I think it's a force requirement.  In fact, I don't know why this cookie
was choosed and what would happen if without this cookie, can anybody tell
me the root reason?

Thanks.


On 8/23/07, Devanand Kumar <devanand at techmahindra.com> wrote:
>
>  *Hi,*
>
> * *
>
> *I want to know the significant of magic cookie… if I am sending a
> transaction number without preceding the magic cookie then what will happen.
> Is it compulsory to give transaction number start with magic cookie?*
>
> * *
>
> * *
>
> *Thanks and Regards,*
>
> *Devanand Kumar *
>
>
>
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-- 
BR
Donald
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