> I have a query regarding the matching 
> rules defined in section 17.2.3, RFC
> 3261, for handling backwards compatibility 
> with RFC 2543  compliant implementations. 
> The matching rules for any request includes 
> matches for To tag and From tag. The earlier 
> draft of RFC 2543 doesn't mandate the To or
> From tag. How should I handle request without 
> To or From tag ?

Section 12.2.1.1 indicates that rfc3261
compliant devices should not change the
uri portion of the To and From headers.
This is so the matching rules from rfc2543
can still work.

" Usage of the URI from the To and From 
  fields in the original request within 
  subsequent requests is done for backwards
  compatibility with RFC 2543, which used 
  the URI for dialog identification.  
  In this specification, only the tags are 
  used for dialog identification.  
  It is expected that mandatory reflection
  of the original To and From URI in 
  mid-dialog requests will be deprecated in 
  a subsequent revision of this specification."

Thus the following are good rules to follow.
1) Don't change To and From uri's during a dialog.
2) Prefer using tags instead of uri's for 
   dialog identity.
3) If a tag is not present, use the uri.

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