Expiration interval in REGISTRATION sequences

Hi,
 
I have a situation where a phone sends a REGISTER message
with "expires=3600" in the Contact Header.
 
The SIP registrar replies back with "Expires: 300"
in the 200 OK response. 
 
In such a situation, which of these 2 values should be taken
as the actual expiration interval ?
 
RFC 3261 -> section 10.3 is slightly obfuscated.
 
In one instance it states that if REGISTER request has an
"expires" parameter or if the request has an
"Expires" header field, that value MUST be taken
as the requested expiration.
 
Then, it also states that registrar MAY choose an expiration
less than the requested expiration interval.
 
Does this mean that the value in the 200 OK message takes
precedence ?
 
thanks,
venkatesh joshi

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