[asterisk-users] Presence SUBSCRIBE/NOTIFY behaviour

[Shaun Bailey]

I'd appreciate some feedback on the behaviour of some tests relating to
presence SUBSCRIBE/NOTIFY.  In the tests no NAT or proxies are involved.

We have a client using a SIP stack accepting requests on one port (eg 5060)
but handling responses on a 'temporary' port.  In other words it sends a
request on a port 'nnnn', quotes port 'nnnn' in the 'Via' header, and then
handles the response to that request on port 'nnnn'.

What we're seeing is that * sends the notification requests to the 'nnnn'
port associated with the SUBSCRIBE request/response rather than 5060.
Naturally this port is no longer open, so they don't get through.  

I'm interested in how * figures out the addressing for the notifications.
Is it from the Via header on the SUBSCRIBE (although I thought this was just
used for responses?) or does it assume that the source of the subscription
is the target for the notifications, or is it through some other means?  Is
it expected behaviour?

OPTIONS requests generated by * are targetted at 5060 so they get through
without any problem.

Any light you could shed on this would be helpful - at this stage I'm just
trying to establish what the correct behaviour is.

Thanks,
Shaun Bailey