[SIPForum-discussion] Periodic NOTIFY for SIP SUBSCRIBE

[Paul Kyzivat]

On 9/18/15 2:50 AM, Ashutosh Panda wrote:
> Thanks to all of you for your response.
>
> I will put the question in a more generic manner.
>
> Consider a use case, where UE is in WiFi network and connected to IMS
> network. If now Wi-Fi network is down or battery removed from the UE,
> there might not be any SIP-De-Registration. But P-Access-Network-Info
> will be set as WiFi access and UE will still be registered at IMS and
> HSS. If UE, switched on in a cellular network and tries to connect to
> IMS, there will be a contention at IMS and HSS. So, there must be
> someway to De-Register the UE when WiFi network is down so that there
> can be a fresh registration in cellular network.
>
> This is why, there was a thought of periodic notify, and if IMS does not
> receive 200OK for a certain SIP-NOTIFY, it will de-register the user
> implicitly.
>
> Any inputs on this will be helpful.

Certainly the UE can subscribe to the "reg" event package. (I thought 
IMS UEs were expected to do so.) Once subscribed, the registrar can send 
a reg event notification whenever it wants, even if nothing is changed, 
and use that as a test that the UE is still connected.

But there will always be a window where the WiFi connection has been 
lost and not yet noticed, when the UE may attempt to reregister over the 
cellular net. So you must have a way to deal with that anyway.

	Thanks,
	Paul

> Thanks
> Ashutosh
>
> On Tue, Sep 15, 2015 at 8:06 PM, Paul Kyzivat <pkyzivat at alum.mit.edu
> <mailto:pkyzivat at alum.mit.edu>> wrote:
>
>     On 9/9/15 4:06 AM, Ashutosh Panda wrote:
>     > Hi All,
>     >
>     > Can there be periodic NOTIFY messages for same event/subscription state
>     > for a SIP SUBSCRIBER for 'reg' event? In other words, can a SIP Server
>     > be configured to send SIP NOTIFY say every one minute even though there
>     > is no change in subscription state?
>
>     It is legal for the server to send messages this way if it wishes. But
>     there isn't any standard way for you to force it to do so. You can of
>     course *poll* it with a SUBSCRIBE whenever you like.
>
>              Thanks,
>              Paul
>
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