[e2e] Satellite networks latency and data corruption

[Detlef Bosau]

Christian Huitema wrote:
> 
> Bottom line, you need to actually measure the system for which you are designing the protocol. There is no "one size fits all" answer to your question.
> 
> > Now, the authors propose a splitting/spoofing architecture:
> >
> > SND----netw.cloud----P1---satellite link----P2-----netw.cloud----RCV
> >
> > P1, P2: "Proxies".
> 
> In theory, there is no particular performance benefit to the proxy architecture. If the transmission protocol uses selective retransmission and large windows, the differences of performance between SND-RCV and P1-P2 are truly minimal. In practice, there is only an advantage if the end-to-end implementations are not well tuned, e.g. do not allow for large windows.
> 

The authors of the aformentioned papers claim three problems.

1.: Packet loss rate / loss differentiation.
2.: Long RTT.
3.: Restrictions of window size.

My remarks on these:
Now, for 3: The authors don´t mention / discuss window scaling.
For 2: A proxy on transport layer cannot shorten the RTT as perceived by
the _application_.
For 1: I´m not quite sure, whether loss differentiation is really a
problem here. From what you say I conclude that this is a borderline
case.

However, conerning long RTT in combination with window size, there may
be a problem left. It may occur that a flow´s fair share of capacity
along the satellite link becomes quite large (this is of course load
dependent). Is it possible, that it takes an unwanted number of "rounds"
then for a sender to 
achieve the appropriate congestion window? I´m not quite sure about
this, because proper window scaling should alleviate this problem.

Detlef Bosau



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