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Re: [Linphone-users] Why Android (Oreo) phones, are actually less reliab


From: Brian J. Murrell
Subject: Re: [Linphone-users] Why Android (Oreo) phones, are actually less reliable with TCP vs. UDP
Date: Sat, 30 Mar 2019 15:00:28 -0400
User-agent: Evolution 3.30.5 (3.30.5-1.fc29)

On Sat, 2019-03-30 at 19:28 +0200, Juha Heinanen wrote:
> 
> I may have lost the point already, but Android phone notices without
> much delay when its network connectivity is lost.  So does Kamailio
> SIP
> proxy (no resoponse to TCP keepalives).

That's the key.  You have to buy into the concept of TCP keepalives.  I
don't.  I think TCP should just wait and resume my session when things
come back.  I want my ssh session to survive the VPN (or even Internet
connection) going down and just pick up where it left off when it did
disappear.  TCP keepalives ruin that.

> When that happens, Kamailio
> automatically un-REGISTERs the SIP client.

Which would indeed close the TCP session and drop the TCP queue,
preventing any backlog to extend retry timers on a blocked TCP session.

> And when Android phone
> notices that network connection is re-established, baresip
> immediately
> reconnects to SIP Proxy and re-REGISTERs its account.

Yeah.  I get it.  It just seems like more work (not for me, granted) to
accomplish what UDP accomplishes without it.

> I don't see how UDP would work any better in such a situation.

It's just that little bit lighter and not racy in not needing to tear
down the TCP session through keep-alives.  If the PBX wants to INVITE
the phone before a keep-alive tears down the TCP session the same
problem occurs, so you still have a failure window.

Cheers,
b.

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