On Thu, 2006-12-14 at 17:32 -0200, Juan Carlos Castro y Castro wrote:
Forget I said that! There's $Ts + $hdr("Expires")! That'll teach me to always RTFA before answering!
Well, you need to be carefull about $hdr("Expires"). This is NOT the only way a UA can specify an expiration delay for a REGISTER request.
If you take a look at the relevant parts of rfc3261 ( http://www.ietf.org/rfc/rfc3261.txt ), you'll see that using an Expires header is only one way of specifying a desired expired duration for the REGISTER. The other way is by using a Contact header parameter (page 60 of the rfc) :
10.2.1.1 Setting the Expiration Interval of Contact Addresses
When a client sends a REGISTER request, it MAY suggest an expiration interval that indicates how long the client would like the registration to be valid. (As described in Section 10.3, the registrar selects the actual time interval based on its local policy.)
There are two ways in which a client can suggest an expiration interval for a binding: through an Expires header field or an "expires" Contact header parameter. The latter allows expiration intervals to be suggested on a per-binding basis when more than one binding is given in a single REGISTER request, whereas the former suggests an expiration interval for all Contact header field values that do not contain the "expires" parameter.
Also note that the expire parameter to a Contact header is totally case-unsensitive ( page 32 of the RFC) :
When comparing header fields, field names are always case- insensitive. Unless otherwise stated in the definition of a particular header field, field values, parameter names, and parameter values are case-insensitive. Tokens are always case-insensitive. Unless specified otherwise, values expressed as quoted strings are case-sensitive. For example,
Contact: <sip:alice@atlanta.com>;expires=3600is equivalent to
CONTACT: <sip:alice@atlanta.com>;ExPiReS=3600
A good example of a very popular SIP UA always using the Contact header parameter method is the Linksys PAP2 ATA. On the other hand, there are also many popular ATAs that use the Expires header method, i.e. Audiocodes MP1XX ATAs. So unless you're in a very controlled environment and you don't care at all to be generic and RFC3261-compliant, you must support both. But be carefull, in my experience this almost always bites you back one day or the other.
Hope this helps, Best Regards,
Jérôme Martin