[asterisk-dev] Subscription Persistence Issues

[George Joseph]

On Wed, Feb 8, 2017 at 6:52 AM, Matthew Jordan <mjordan at digium.com> wrote:

>
>
> On Tue, Feb 7, 2017 at 1:16 PM, George Joseph <gjoseph at digium.com> wrote:
>
>> Greetings All,
>>
>> I've been working on the (many) issues with recreating inbound
>> subscriptions after an asterisk restart.  I have an approach that works but
>> has a drawback:  We can recreate the subscription on startup from the data
>> we persist and can even send a NOTIFY to each subscriber BUT with the
>> current version of pjproject, we can't actually set the expiration timer.
>> I have a pjproject patch ready that allows us to set tie timer but the
>> drawback is that this approach will only work with bundled pjproject or a
>> patched version of your own.
>>
>> There's an alternative though...   When asterisk restarts, instead of
>> sending 'active' NOTIFYs to each subscriber, we could send
>> 'terminate,probation' instead.  The RFCs say that a "client SHOULD retry at
>> some later time".  While this approach will work with any version of
>> pjproject there are issues here as well.  The first issue is the word
>> 'SHOULD'.  There's no guarantee that the client will actually resubscribe.
>> The second issue is the extra SUBSCRIBE/OK/NOTIFY/OK exchange between
>> asterisk and the client at startup.  We can tell the client to retry not
>> before a random interval similar to how we stagger sending OPTIONS messages
>> at startup but it's still an extra 4 packets per subscription.
>>
>> Neither approach is harder or easier than the other to implement.  It's
>> just a matter of backwards compatibility vs extra traffic and the 'SHOULD'
>> uncertainty.
>>
>> Thoughts?
>>
>>
> If you go with the first approach, do the changes to pjproject to fix the
> expiration timer issues cause any API changes? Or is it merely fixing a bug
> in pjproject?
>

pjproject already has an internal API to set the timer on a subscription so
the patch is creating a public wrapper for it.


>
> --
> Matthew Jordan
> Digium, Inc. | CTO
> 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
> Check us out at: http://digium.com & http://asterisk.org
>
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-- 
George Joseph
Digium, Inc. | Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org
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