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Re: Target numbers for setup time (Re: Keeping up data channel)

From: Roman Shpount <roman@telurix.com>
Date: Fri, 22 Jun 2012 13:54:59 -0400
Message-ID: <CAD5OKxv2_9U_-udCE=CQpfVD634SeXGJuma91mMh7YEMbT0dSA@mail.gmail.com>
To: Harald Alvestrand <harald@alvestrand.no>
Cc: public-webrtc@w3.org
On Fri, Jun 22, 2012 at 1:09 PM, Harald Alvestrand <harald@alvestrand.no>wrote:

> On 06/22/2012 05:58 PM, Cullen Jennings (fluffy) wrote:
>
>> On Jun 13, 2012, at 5:29 , Randell Jesup wrote:
>>
>>  How far down do you think we have to drive the setup time before you
>>>> would not call it "abysmal"?
>>>>
>>>
>> I'd probably consider above 250 ms abysmal but good news I don't see any
>> problem with getting it down around 100 ms in when both endpoints are in a
>> single country.
>>
>>  Coast-to-coast US is ~4800 km, so RTT (9600 km) is 32 ms (speed of light
> is 300 km/msec).
>
> So, without considering processing time, 3 RTT is 100 msec, 7 RTT is
> "abysmal".
>
> There are bigger countries than the US, but this will do for a
> back-of-the-envelope.
>
>
IP packets rarely travel in straight lines and typically encounter 2-3
routers along the way. In US, from east to west coast, between the data
centers, 60-70 ms are typical. Residential to residential are about 80-100
ms. So, 3 RTT in real life are "abysmal" by this standard.

More reasonable point of view is that normally designed call setup should
take 2 RTT (offer, answer and connectivity check in offerer's direction,
offerer's connectivity check response and connectivity check in answerer's
direction, answerer's connectivity check response). Everything else is
adding latency for the sake of bad desing.
_____________
Roman Shpount
Received on Friday, 22 June 2012 17:55:31 UTC

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