[Sip] About register expiration

	Hi,

	I have a question the SIP standard definitions for "expires"
handling in the registration.

	This is what I see in paragraph 10.3:
	The registrar returns a 200 (OK) response.  The response MUST
contain Contact header field values enumerating all current bindings.
Each Contact value MUST feature an "expires" parameter indicating its
expiration interval chosen by the registrar.  

	From this I understand that the 200OK must include expires
parameter in the contact header.
	On the other hand when I look at message examples in paragraph
24.1, I see the following:


	   F1 REGISTER Bob -> Registrar

	       REGISTER sip:registrar.biloxi.com SIP/2.0
	       Via: SIP/2.0/UDP
bobspc.biloxi.com:5060;branch=z9hG4bKnashds7
	       Max-Forwards: 70
	       To: Bob <sip:bob@biloxi.com>
	       From: Bob <sip:bob@biloxi.com>;tag=456248
	       Call-ID: 843817637684230@998sdasdh09
	       CSeq: 1826 REGISTER
	       Contact: <sip:bob@192.0.2.4>
	       Expires: 7200
	       Content-Length: 0


	   F2 200 OK Registrar -> Bob

	        SIP/2.0 200 OK
	        Via: SIP/2.0/UDP
bobspc.biloxi.com:5060;branch=z9hG4bKnashds7
	         ;received=192.0.2.4
	        To: Bob <sip:bob@biloxi.com>;tag=2493k59kd
	        From: Bob <sip:bob@biloxi.com>;tag=456248
	        Call-ID: 843817637684230@998sdasdh09
	        CSeq: 1826 REGISTER
	        Contact: <sip:bob@192.0.2.4>
	        Expires: 7200
	        Content-Length: 0

	Where the registrar does not set the expires parameter in the
contact header, but leaves it in the Expires header.

	Which is correct? Is it allowed to have both Expires header and
expires parameter for Contact headers in the 200OK?


Regards,
Rachel Danor