Re: [Bloat] Random idea in reaction to all the discussion of TCPflavours - timestamps?

[Wesley Eddy <wes@mti-systems.com>]

On 3/20/2011 9:28 PM, david@lang.hm wrote:
> On Mon, 21 Mar 2011, Jonathan Morton wrote:
>
>> On 21 Mar, 2011, at 12:18 am, david@lang.hm wrote:
>>
>>>> 0) Buffering more than 1 second of data is always unacceptable.
>>>
>>> what about satellite links? my understanding is that the four round
>>> trips to geosync orbit (request up, down, reply up down) result in
>>> approximatly 1 sec round trip.
>>
>> That is true, but it doesn't require more than a full second of
>> buffering, just lots of FEC to avoid packet loss on the link. At those
>> timescales, you want the flow to look smooth, not bursty. Bursty is
>> normal at 100ms timescales.
>>
>> What I've heard is that most consumer satellite links use split-TCP
>> anyway (proxy boxes at each end) thus relieving the Internet at large
>> from coping with an unusual problem. However, it also seems likely
>> that backbone satellite links exist which do not use this technique. I
>> heard something about South America, maybe?
>
> I've heard that they do proxy boxes at each end for common protocols
> like HTTP, but they can't do so for other protocols (think ssh for example)
>
>> Anyway, with a 1-second RTT, the formula comes out to max 1 second of
>> buffering because of the clamping.
>
> and what if you have a 1 second satellite link plus 'normal internet
> latency', or worse, both ends are on a satellite link, giving you a
> 2-second+ round trip time?
>
> if you don't have large enough buffers to handle this, what happens?
>


Propagation delay to a geosynchronous relay is ~125 ms.  Round-trip 
propagation delay contributes ~500 ms, so it isn't quite as bad as you 
think, though still long.

Many tricks are played with accelerator gateways to improve bulk 
transfer throughput for TCP users (see e.g. RFC 3135).

There may be a challenge in debloating the devices that support such 
links, as their buffers and the functions they serve optimize other 
metrics (e.g. low packet loss rate, bulk transfer throughput, etc.).

-- 
Wes Eddy
MTI Systems