Re: [pntaw] Real-time media over TCP

[<[e-mail]>]

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