Newsgroups: comp.protocols.tcp-ip
Path: utzoo!utgpu!cunews!jstewart
From: jstewart@ccs.carleton.ca (John Stewart)
Subject: Re: When is a link saturated?
Message-ID: <1991Jan21.141530.7031@ccs.carleton.ca>
Organization: Carleton University, Ottawa, Canada
References: <9101150900.AA08526@jerry.inria.fr> <9101150724.AA12358@mcsun.EU.net> <24@prang.TEST.Vitalink.COM> <1991Jan20.040130.18339@quick.com>
Date: Mon, 21 Jan 1991 14:15:30 GMT

In article <1991Jan20.040130.18339@quick.com> srg@quick.com (Spencer Garrett) writes:
>-> I don't understand why the "remember the first exchange" is necessary. 
>-> Both telnet and rlogin use a reserved port number that appears in either
>-> the source or destination TCP port fields on *every* packet that is
>-> routed for the entire session.
>
>Alas, no.  A server is free to answer the connection request
>with a different port number, and they commonly do.  (The reason
>for this eludes me.  It is permitted by the RFC's, but not
>required or particularly encouraged.)

The main reason for doing so is to facilitate multiple sessions.  For example
if 10 people telnet to a machine, each user will get their own telnetd 
process communicating to them via a unique set of ports.  Now imagine how
difficult this would be to do if you could only have one process running 
connected to the well known telnet port.
-- 
---
Artificial Intelligence: What some programmers produce.
Artificial Stupidity:    What the rest of us produce.