Re: multiple connections

[Franco Travostino <travos@nortelnetworks.com>]

A bit of Related Work ... On the forever-young 1 vs. N TCP connections
subject, you may be interested in the results shown in the '97 "An
Application-Level Solution to TCP's Satellite Inefficiencies" paper
(available at http://jarok.cs.ohiou.edu/projects/satellite/) and on Sally
Floyd's comment hereafter. The intersection with satellite links is quite
accidental, and the arguments/results apply above and beyond satellite links.

-franco

>From majordom@ISI.EDU Fri Dec  6 23:05:58 1996
>To: fred@cisco.com (Fred Baker)
>Cc: end2end-tf@isi.edu
>Subject: Re: Related paper/re:satellites
>Date: Fri, 06 Dec 1996 23:05:47 PST
>From: Sally Floyd <floyd@ee.lbl.gov>
>Sender: owner-end2end-tf@ISI.EDU
>Precedence: bulk
>Content-Length: 2309
>X-Lines: 44
>
>Fred -
>
>>You might be interested in reviewing this paper, which is what I'm
>>discussing with Karen Hansen, Dan Shell, and the folks from Comsat. It
>>relates to some TCP/Satellite work being done at NASA Lewis Research
>>Center.
>
>Basically (from a quick read), the paper, on "An Application-Level
>Solution to TCP's Satellite Inefficiencies", recommends breaking a
>single TCP connection into multiple connections at the
>application level, to increase throughput on satellite circuits.
>It is not too surprising that this increases the TCP throughput, but it
>is still not a good idea.  For a single TCP connection, a single packet
>drop results in the throughput for that connection being cut by half,
>and then increased by roughly one packet per RTT.  For a TCP connection
>that has instead been separated into N different TCP connections, a
>single packet drop results in one of the N connections, receiving
>1/N-th of the total bandwidth, having its throughput cut in half.  Thus
>the bandwidth of the aggregate connection has its bandwidth reduced to
>(1 - 1/(2N))-th of its former bandwidth - that is, the larger the value
>for N, the smaller the aggregate bandwidth is cut.  And then, because
>each TCP connection continues to increase its congestion window by one
>packet per RTT, for those TCP connections that have not yet reached the
>receiver's advertised window, the aggregate TCP connections together
>increase their bandwidth by up to N packets per RTT.
>
>Summarizing, splitting a TCP connection into N separate connections
>simply increases the aggressiveness of the TCP congestion control.
>Meaning that this TCP is now more likely to "steal" bandwidth from
>other TCP connections in times of congestion.  And increasing the
>aggressiveness of the TCP congestion control too far (by choosing N too
>large) is counterproductive even for the aggregate TCP connection, as
>the paper shows.
>
>I would suggest that this is exactly the kind of development for which
>[RED is needed].
>
>- Sally
>
>
>