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Path: utzoo!utgpu!water!watmath!clyde!att!pacbell!ames!ncar!gatech!galbp!wittsend..LBP.HARRIS.COM!mhw
From: mhw@wittsend..LBP.HARRIS.COM (Michael H. Warfield)
Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip
Subject: Re: FTP server question
Message-ID: <5093@galbp.LBP.HARRIS.COM>
Date: 24 May 88 17:40:11 GMT
References: <535@interlan.UUCP>
Sender: news@galbp.LBP.HARRIS.COM
Reply-To: mhw@wittsend.LBP.HARRIS.COM (Michael H. Warfield)
Distribution: na
Organization: Harris/Lanier Network Knitting Circle
Lines: 43

In article <535@interlan.UUCP> backman@mercury.UUCP (Larry Backman) writes:
>
>	Packet 1 contains a FTP servers Hello message without a CR/LF.
>	Packet 2 contains the CR/LF.
>
>	RFC 959, section 4.2 of the DDN protocol handbook Page 2-773 and 2-774
>	clearly state:
>
>	       "A reply is defined to contain the 3 digit code, followed
>		by Space <SP>, followed by one line of text (where some
>		maximum line length has been specified), and terminated by the
>		Telnet end of line code."
>
>
>	At first glance, the FTP server is at fault.  However, in their
>	defense,  FTP uses TCP, a stream oriented protocol, to ensure 
>	reliable delivery.  This means that the data from a stream can 
>	come out as one single packet, or in the worst case, dribble out
>	as a stream of single bytes.  So in the second case, the split of
>	the FTP message, and the TELNET CR/LF is not so bad.
>

	More to the point is the fact that, to an application, data on a
tcp/ip connection is a structureless stream of bytes.  Any structuring is
imposed by a higher level (i.e.  ftp client / ftp server).  This implies that
tcp/ip packet boundries have no significance to the application (ftp) and may
not even be discernable in many implimentations.  This applies even if there
is a PUSH flag on the tcp/ip packet.  It does not, of course, apply if an
urgent flag is on the data, indicating the last byte of the packet is an
URGENT boundry.  But, then again, ftp does not use that flag for anything.

	RFC 959 concerns the ftp protocol itself and does not relate to
tcp/ip packets or structuring.

---
Michael H. Warfield		| gatech.edu!galbp!wittsend!mhw
  (404)-329-8139		| mhw@wittsend.LBP.HARRIS.COM
An optimist believes we live in the best of all possible worlds.
A pessimist is sure of it!
Michael H. Warfield		| gatech.edu!galbp!wittsend!mhw
  (404)-329-8139		| mhw@wittsend.LBP.HARRIS.COM
An optimist believes we live in the best of all possible worlds.
A pessimist is sure of it!