Hi, I have copied some statements from few RFCs as shown below.
>From RFC 3265 A natural consequence of the behavior described in the preceding sections is that an immediate fetch without a persistent subscription may be effected by sending a SUBSCRIBE with an "Expires" of 0. Of course, an immediate fetch while a subscription is active may be effected by sending a SUBSCRIBE with an "Expires" equal to the number of seconds remaining in the subscription. >From RFC 3680 However, notifications triggered as a result of a fetch operation (a SUBSCRIBE with Expires of 0) SHOULD result in the full state of all contacts for all registrations to be present in the NOTIFY. 1) From above paras, Is the Fetch operation done by sending Initial(First) SUBSCRIBE with Expires: 0 ? Which should return in NOTIFY with FULL state. How to effect the Fetch operation in the middle of an active dialog from above. How to send this Expires: with remaining seconds in the subscription. This may create race condition with the Notifier, while calculating the "remaining seconds in the subscription). >From RFC 3856 In fact, behavior of the presence agent for handling a SUBSCRIBE request with Expires of zero is no different than for any other expiration value; pending or authorized SUBSCRIBE requests result in a triggered NOTIFY with the current presentity and subscription state. It is also possible to fetch the current presence state, resulting in a one-time notification containing the current state. This is accomplished by sending a SUBSCRIBE request with an immediate expiration. 2) From first para here, In case a SUBSCRIBE with Expires: 0 is sent, then NOTIFY with current presentity state is received from the Notifier. But before this NOTIFY if 200 OK response is received from the Notifier for that SUBSCRIBE(with Expires:0), then the dialog would have been cleared by the Subscriber. Then what is the use of this NOTIFY ? What is the use case here ? 3) From second para here, As per this RFC, a SUBSCRIBE with immediate expiration will result in Fetch operation returning FULL state. What does this immediate expiration mean here ? Is it some small expiration value ? If so then the Notifier may take this as a newly requested Subscribe duration and may honor it also, which may not be desired by the Subscriber. Any clarity on the above statements is appreciated. thanks & regards Santhana _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
