RFC 310 (rfc310) - Page 1 of 7
Another Look at Data and File Transfer Protocols
Alternative Format: Original Text Document
Network Working Group A. Bhushan
Request for Comments: 310 MIT-MAC
NIC: 9261 April 3, 1972
Another Look At Data And File Transfer Protocols
Our experience with ad hoc techniques of data and file transfer over
the ARPANET together with a better knowledge of terminal IMP (TIP)
capabilities and Datacomputer requirements has indicated to us that
the Data Transfer Protocol (DTP) (see ref 1) and the File Transfer
Protocol (FTP) (see ref 2) could undergo revision. Our effort in
implementing DTP and FTP has revealed areas in which the protocols
could be simplified without degrading their usefulness.
This paper suggests some specific changes in DTP and FTP that should
make them more useful and/or simplify implementation. The attempt
here is to stimulate thinking so that we may come up with a better
protocol at the forthcoming Data and File Transfer Workshop (see ref
3).
Experience to Date
A number of ad hoc techniques of transmitting data and files across
the ARPANET already exist. Perhaps, the most versatile of these
existing methods is the TENEX "CPYNET" system. The "CPYNET" system
uses an ad hoc or interim file transfer protocol developed by Ray
Tomlinson and others at BBN to transmit files among the TENEX systems
on the ARPANET. [Private Communication with Bill Crowther, BBN.]
In CPYNET, the using process goes through the Initial Connection
Protocol (ICP) to server socket 7, establishing a full-duplex
connection with an 8-bit byte size. Control information, including
user name, password, command (read, write, or append), file name, and
byte size for the data connection is transmitted from the using
process to the serving process. The original full-duplex connection
is then closed, and a new full-duplex connection is established using
the original socket numbers but with possibly a different byte size.
The file is now transmitted on this newly established connection.
The end-of-file is indicated by closing the connection (the mode of
transfer is thus similar to DTP "indefinite bit-stream").
CPYNET has been used quite extensively for transfer of TENEX system
files. Because data is not reformatted, and because the optimum
connection byte size may be used for data transfer, CPYNET is quite
efficient. The PDP-10 (and there are quite a lot in the ARPANET)
works more efficiently with a 36 bit byte size which minimizes
packing and unpacking of data, and increases effective I/O speed
Bhushan