Path: utzoo!utgpu!watserv1!watmath!att!pacbell.com!ucsd!ucbvax!SICS.SE!craig
From: craig@SICS.SE (Craig Partridge)
Newsgroups: comp.protocols.tcp-ip
Subject: More on TCP Performance Limits
Message-ID: <9101111221.AA08912@garuda.sics.se>
Date: 11 Jan 91 12:21:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 24


There seems to be a lot of misinformation running around.

The end-to-end performance of a TCP connection is limited by two different
factors:

    (1) The window size.  Because the window size determines how much
    unacknowledged data can be in flight, the maximum bandwidth a
    connection can achieve is the window size divided by the round-trip
    time.

    (2) The sequence space size.  To ensure that you don't get sequence
    space wrap (two different instances of byte #37 active at the
    same time), TCP places time limits (which depend on IP flushing
    packets of a certain age) on how fast you can cycle through the
    sequence space.

Right now (1) is the usual limit on throughput.  I believe you have to get
substantially past FDDI speeds for (2) to be a problem.

RFCs 1072 and 1185 discuss these issues in more detail.

Craig Partridge
(on sabbatical at the Swedish Institute of Computer Science).