Say an End-point B plays the role of a UAS in the initiation phase of the
call, and then later on plays the role of a UAC (for instance when it sends
a BYE request)
B sets the value of the 'Tag' parameter in the 'From' field to be the same
as the tag value of the 'To' field from the first transaction. By doing so
it lets A know who is exactly the B instance that hangs up the call (in case
there is possibly more than one instance of B). 

However when an end point just initiates a call what's the point of using
tag in the from header? What info does it add on top of the Call-Id? Can
multiple instances of B can initiate a call with the same Call-Id? any
specific example , which may illustrate a relevant situation?

Uri


=======================================================================
Uri Baniel - Distinguished Member of Technical Staff - Motorola  
Tel: (847) 632 4616; Fax: (847) 632 3963; 
"Learning that does not daily increase will daily decrease. - EWC
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