Hadriel Kaplan wrote:
> I wonder if we really need the from-tag at all for this type of thing.  
> Forget for the moment about any of this and just think of the current Call-ID 
> and tags, and assume there were no B2BUA's.  Is there ever a case where a UAC 
> would generate a request with the same Call-ID as a previous request, but a 
> different from-tag?

Registration, but I think that is probably out of scope for what you are
considering!

>   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.

> -hadriel
>   

Michael
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