Re: Changed From Tag in Spiral Request

On Tue, 2009-09-01 at 14:13 +0530, Manjunath Warad wrote:
> If a UA receives a request in a spiralled way then shouldn't the
> From Tag and Call-ID same as the originated request?

> Should the UA accept the received request as spiral if call-ID is
> same and From tag is different? Please let me know if there is any business
> use case of such scenario if you have come across.

> Since the match algo is not well defined for spiral in RFC, we need
> a reference.

Strictly speaking a UA cannot receive a spiraled request, since the
request cannot have passed through the UA before.  A UA can receive a
"merge" request, that is, a request which is another fork of a request
that it has received before.  Merged requests are detected per section
8.2.2.2 of RFC 3261:  the Call-Id, the from-tag, and the CSeq are the
same.  As you notice, if the Call-Id's are the same, the from-tag's must
be the same, but if some intermediate element has modified the from-tag,
it is clear that the UA should consider the requests to not be merged
requests.

In regard to a proxy, which can receive a spiraled request, that is, a
request one of whose ancestral requests passed through the proxy:  The
proxy does not need to be aware that the request is spiraled, since it
only needs to recognize "hop-by-hop transactions", which are identified
by the branch parameter value of the topmost Via header.

Dale


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