C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Mon, 25 Oct 2004 18:33:58 -0300 (CLST)

FTP relies on TCP for error detection and correction -
http://www.ietf.org/rfc/rfc0959.txt (see section 3.5)

TCP is a *reliable* transport layer protocol -
http://en.wikipedia.org/wiki/Transmission_Control_Protocol
This document notes that the TCP checksum is relatively weak (16 bits),
but that further checksums at lower levels make that more secure.  Not as
secure as you might expect, though, according to -
http://citeseer.ist.psu.edu/stone00when.html

Reliable file transfer controls GridFTP file transfers as a web service -
http://www-unix.globus.org/toolkit/docs/3.2/rft/  GridFTP is based on FTP
- http://highenergy.phys.ttu.edu/projects/sam/GridFTP.htm and the
extensions cover things like multiple streams, but NOT checksums (however,
it *does* require a more complete FTP implementation than normal).

So RFT uses GridFTP uses FTP uses TCP checksums (as far as I can tell).

So why do people think that RFT is more reliable than FTP?  The most
likely scapegoat is poor FTP implementations that don't flag incomplete
file transfer.  There does not appear to any additional checksum in
addition to TCP.

Andrew

-- 
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