On Tue, 2008-12-09 at 10:04 +0000, Michael Procter wrote:
The to-tag we needed to identify forked responders generating
unique early-dialogs with a common Call-ID, but why did we need the
UAC to generate a from-tag? (I'm feeling dumb that I can't figure out
the answer)
In the reverse direction, the presence of a to-tag in a request
indicates an in-dialog request. Therefore, requiring a from-tag
ensures
that requests in the reverse direction can have a to-tag, and thus be
correctly treated as in-dialog.
I'm looking at the code in sipX that works with tags to determine the
status of a SIP message, and though the from-tag is not logically
necessary, it does make the code simpler, as the To and From URIs are
handled more symmetrically.
In addition, it allows the SIP element to extract and compare only the
tags, rather than having to compare the To/From URIs (as is required
in
RFC 2543), which is always fraught with problems.
Dale
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