Re: [pntaw] Real-time media over TCP

<Markus.Isomaki@nokia.com> Wed, 09 October 2013 17:46 UTC

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From: <Markus.Isomaki@nokia.com>
To: <pkyzivat@alum.mit.edu>, <pntaw@ietf.org>
Thread-Topic: [pntaw] Real-time media over TCP
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Date: Wed, 9 Oct 2013 17:38:55 +0000
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References: <CAGTXFp92jSzQz05uHngzscz88n=fT_JPbEvQRxgeUUqPVRQUyQ@mail.gmail.com> <52244DD7.1020900@alvestrand.no> <BLU405-EAS183E36A927CA42270B6936D93300@phx.gbl> <522590EE.7070508@alvestrand.no> <C632A223-A55A-47F4-B083-9BDC447DA959@cisco.com> <52262657.3080208@alvestrand.no> <A2C315DB-1882-4BD1-A8C0-E8AF7DEA48F4@cisco.com> <00ca01cec387$f881cae0$e98560a0$@co.in> <52538AC4.5060500@alvestrand.no> <52557D47.3050402@alum.mit.edu>
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Subject: Re: [pntaw] Real-time media over TCP
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Hi Paul,

Paul Kyzivat wrote:
> 
> On 10/8/13 12:32 AM, Harald Alvestrand wrote:
> 
> > Don't forget the (likely) case where the destination is also reached
> > through a TURN server, so that the path is
> >
> > user 1->TCP->TURN server 1->UDP->TURN server 2->TCP->user 2
> >
> > For extra irony, the two clients may be using the same TURN service,
> > so that the UDP hop is an intra-datacenter or even intra-machine hop
> > :-)
> 
> If that happens, its time to seek out a new TURN server vendor.
> A good one should be able to figure this out and optimize it.
> 

I think it can happen even if the vendor and the service provider do all they can. For instance if both endpoints are behind a UDP blocking firewall and can only open TCP connections. So unless the endpoints support TCP-based ICE candidates, I think they need to connect to their respective TURN relays and only via them they can reach each other's TURN-allocated UDP candidates. So the transport will be split into 3 hops: TCP - UDP - TCP, where the UDP part can be potentially very short.

Or is there some way to optimize from that? If I've understood correctly, ICE-TCP with TURN-allocated TCP ports would allow using just a single relay in the above scenario. It would be thus be better in case if the relays used by the endpoints were NOT in the same DC.

Markus