Re: [Linphone-users] Why Android (Oreo) phones, are actually less reliable with TCP vs. UDP

[Brian J. Murrell]

On Sat, 2019-03-30 at 11:22 -0400, Greg Troxel wrote:
> 
> "could"??

Could from a technical perspective, not philosophical perspective.  I
don't disagree with that philosophical perspective mind you, not at
all.

> Agreed that this could happen this way.  But why is the TCP packet
> lost?

There's no TCP packet lost.  Just delayed in a backoff-time-retry
cycle.

> Why doesn't it just arrive when the phone is awake, from whatever
> queue
> it was in?

It does.  But only when the PBX's TCP stack is ready to send it when
it's most recent (backing off, remember) timeout expires.  By then, if
the packet has been waiting a while in the queue, could be too long.

>   What is the mechanism by which it is dropped?

Not dropped, just delayed by TCP's retry-backoff-timeout retransmission
cycle.

> As I see it, this is a suboptimal system design, relying on a loss
> recovery mechanism to retry when there is not actual loss in the
> usual
> sense, instead of having a plan to avoid loss

No loss.  Just delay.

> That's what the IETF draft is about.

Right.  But has anyone actually implemented that yet?

> They weren't, but there was congestion loss which was erratic, and
> they
> were flaky where they would not work for a long time.  Nobody
> expected
> TCP connections to survive these needing-repair or wet-phone-line
> kind
> of outages.

Why wouldn't they?  I would think it would have been completely
expected, even designed for that if a link just goes silent, everything
just waits for it to come back.

> You can do this.  But it's not bad to have an ICMP network
> unreachable -
> just perhaps not what you want.

I don't think I agree.  For my money, an ICMP network unreachable
reflects a permanent lack of route somewhere.  Temporary outages should
be silent and allowed to to resume when repaired.

> That's the intent of the new SIP/push protocol spec.

But without any client and/or server implementations, we have to wait
and do the best with what we have currently.

> Have you turned off v4?  How does that work for you?

I do have some machines here in the house where I have turned off v4,
yes.  But that is outside of the realm of SIP.

> Or do you just  mean you can talk to your sip server over v6 just
> about
> always?

Indeed.

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