I-D ACTION:draft-shepard-tcp-4-packets-3-buff-00.txt

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	Title		: When TCP Starts Up With Four Packets Into Only Three Buffers
	Author(s)	: C. Partridge, T. Shepard
	Filename	: draft-shepard-tcp-4-packets-3-buff-00.txt
	Pages		: 5
	Date		: 1997-08-01
	
Sally Floyd has proposed that TCPs start their initial slow start by
   sending as many as four packets (instead of the usual one packet) as
   a means of getting TCP up-to-speed faster.  (Slow starts instigated
   due to timeouts would still start with just one packet.)  Starting
   with more than one packet might reduce the start-up latency over
   long-fat pipes by two round-trip times.  This proposal is documented
   further in [1] and in [2] and we assume the reader is familiar with
   the details of this proposal.
 
   On the end2end-interest mailing list, concern was raised that in the
   (allegedly common) case where a slow modem is served by a router
   which only allocates three buffers per modem (one buffer being
    transmitted while two packets are waiting), that starting with four
   packets would not be good because the fourth packet is sure to be
   dropped.
 
   Vern Paxson replied with the comment (among other things) that the
   four-packet start is no worse than what happens after two round trip
   times in normal slow start, hence no new problem is introduced by
   starting with as many as four packets.   If there is a problem with a
   four-packet start, then the problem already exists in a normal slow-
   start startup after two round trip times when the slow-start
   algorithm will release into the net four closely spaced packets.
 
   This memo is to document that in the case of a 9600 bps modem at the
   edges of a fast Internet where there are only 3 buffers before the
   modem (and the fourth packet of a four-packet start will surely be
   dropped), no significant degradation in performance is experienced
   with a four-packet start when compared with a normal slow start
   (which starts with one packet).

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