Re: [pntaw] Real-time media over TCP

Harald Alvestrand <harald@alvestrand.no> Wed, 16 October 2013 12:02 UTC

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Date: Wed, 16 Oct 2013 14:02:51 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [pntaw] Real-time media over TCP
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On 10/15/2013 06:15 PM, Dan Wing wrote:
> On Oct 14, 2013, at 11:02 PM, Tirumaleswar Reddy (tireddy) <tireddy@cisco.com>; wrote:
>
>>> -----Original Message-----
>>> From: pntaw-bounces@ietf.org [mailto:pntaw-bounces@ietf.org] On Behalf Of Dan
>>> Wing (dwing)
>>> Sent: Tuesday, October 15, 2013 5:31 AM
>>> To: Markus.Isomaki@nokia.com
>>> Cc: pntaw@ietf.org; partha@parthasarathi.co.in
>>> Subject: Re: [pntaw] Real-time media over TCP
>>>
>>>
>>> On Oct 14, 2013, at 12:06 PM, Markus.Isomaki@nokia.com wrote:
>>>
>>>> Hi,
>>>>
>>>> In practice I doubt you find many situations where UDP is completely blocked
>>> but incoming TCP connections from anywhere are allowed.
>>>
>>> Agreed.
>>>
>>> But if both ends are trying to communicate with each other, their
>>> communications will appear as a TCP simultaneous-open.  That could (in fact,
>>> "should") work across a firewall because the firewall will see an outbound SYN
>>> to a host/port after which it will see an inbound SYN from that same
>>> host/port.
>> But firewall TCP inspection causes the inbound SYN from the same host/port to be dropped (Firewalls typically do not permit TCP simultaneous-open). Even with NAT as per the survey results in ICE TCP (http://tools.ietf.org/html/rfc6544#appendix-A) TCP simultaneous-open worked only in roughly 45% of the cases.
> If avoiding TURN improves the user experience, and IT policy says TCP is allowed, I expect firewall vendors would make sure TCP simultaneous open works.
>
>
If something improves the user experience if it is possible to do it, 
but the basic functionality works without it, and it's unclear whether 
the special circumstances under which it's going to improve the user 
experience in fact exist in the field, I think that's perfect for a MAY 
implement.