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From: ejm@ejmmips.NOC.Vitalink.COM (Erik J. Murrey)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: When is a link saturated?
Message-ID: <24@prang.TEST.Vitalink.COM>
Date: 16 Jan 91 16:27:57 GMT
References: <9101150900.AA08526@jerry.inria.fr> <9101150724.AA12358@mcsun.EU.net>
Sender: usenet@prang.TEST.Vitalink.COM
Reply-To: ejm@ejmmips.NOC.Vitalink.COM (Erik J. Murrey)
Organization: Vitalink Communications
Lines: 28
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In article <9101150900.AA08526@jerry.inria.fr>,
Christian.Huitema@MIRSA.INRIA.FR (Christian Huitema) writes:
> .... One can indeed use the "protocol identifier" (TCP, UDP,
> ICMP..) and place different priorities to different protocols, but I
am a bit 
> puzzled by cisco's assertion that they give "telnet" traffic precedence over 
> "ftp": after the first synchronisation, neither the IP headers nor the TCP 
> header bear any indication of the application layer protocol. The only
way to 
> make this correlation is to "remember the first exchange"; but if parallel 
> routes can be used, there is not even a garantee that the synchronisation 
> packets and the data packets will follow the same route! One should also note
> that if IP segmentation is used, the TCP header is only present in the first
> segment...
> 
 
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.  The one exception is when IP gets
fragmented, which is rare in modern WAN's with current TCP implementations.


... Erik
---
Erik Murrey
Vitalink Communications
ejm@NOC.Vitalink.COM   ...uunet!NOC.Vitalink.COM!ejm