FTPSRV - Tenex extension for paged files (RFC0683)

Publication Summary

Country	United States
Language	English (United States)
Related Person(s)	(AUTHOR)  R. Clements

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RFC 683, NIC 32251

FTPSRV - TENEX FTP EXTENSIONS FOR PAGED FILES

R. Clements - BBN - 3 April 75

1 Introduction

In response to a long-known need for the ability to transfer TENEX paged

files over the net via FTP, the TENEX FTP implementation has been extended.

This implementation is an extension to the "OLD" protocol (RFC 354). It

was built after useful discussions with Postel, Neigus, et al. I do not mean

to imply that they agreed that this implementation is correct, nor for that

matter do I feel it is correct. A "correct" implementation will be negotiated

and implemented in the "NEW" protocol (RFC 542), if funding ever appears for

that task.

2 The Problem(s)

This extension attacks two separate problems: Network reliability and

TENEX disk file format's incompatibility with FTP. A checksummed and

block-sequence-numbered transmission mode is seriously needed, in my opinion.

This mode should also allow data compression.

It is also necessary to handle paged, holey TENEX files. This latter

problem, seriously needed for NLS, is the motivation for the current

extension.

The former problem requires a new MODE command, if done correctly;

probably two MODEs, to allow data compression in addition to checksumming.

Actually, I think that is the tip of an iceberg which grows as 2**N for

additional sorts of modes, so maybe some mode combination system needs to be

dreamed up. Cf the AN, AT, AC, EN, ET, EC TYPEs. Also, one should be able to

use MODE B and MODE C together (NEW protocol) to gain both the compression and

restart facilities if one wanted.

The second problem, TENEX files, are probably a new kind of STRUcture.

However, it should be possible to send a paper tape to a disk file, or vice

versa, with the transfer looking like a paged file; so perhaps we are dealing

with a data representation TYPE. This argument is a bit strained, though, so

a paged STRUcture is quite likely correct. I admit to feeling very unsure

about what is a MODE, what is a TYPE and what is a STRUcture.

3 The (Incorrect) choices made

Having decided that new MODEs and STRUctures were needed, I instead

implemented the whole thing as a single new TYPE. After all, I rationalize,

checksumming the data on the network (MODE) and representing the data in the

processing system as a checksummed TYPE are really just a matter of where you

draw the imaginary line between the net and the data. Also, a single new TYPE

command reduced the size of the surgery required on the FTP user and server

programs.

4 Implementation details

The name of the new TYPE is "XTP". I propose this as a standard for all

the Key Letter class of FTP commands: the "X" stands for "experimental" --

agreed on between cooperating sites. The letter after the "X" is signed out

from the protocol deity by an implementor for a given system. In this case,

"T" is for TENEX. Subsequent letter(s) distinguish among possibly multiple

private values of the FTP comm...

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