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Network Working Group H. Brodie Request for Comments #250 UCLA-NMC NIC #7691 Computer Science Categories: D5, D7 7 October 71 Updates: None Obsoletes: None

                   Some Thoughts on File Transfer
 There are several aspects of the proposed Data Transfer Protocol (RFC
 #171) and File Transfer Protocol (RFC #172) which we believe could
 use further clarification and perhaps revision.  Interest in
 transferring larger amounts of data than is typically sent via the
 usual TELNET connection is increasing, and at least at UCLA-NMC
 implementation attempts have pointed out several difficulties with
 the proposed protocols.
 First, and probably most easily decided, is the ambiguity in RFC #171
 with regards to the sequence number field of the descriptor and count
 transaction.  The description provided for the transaction header
 provides for 16 bit sequence number.  However, the sequence number
 field in the error codes transaction only provides for 8 bits.  We
 are of the opinion that 8 bits is sufficient for a sequence number
 field.  If the sequence number is reduced to 8 bits, and the two NUL
 bytes are deleted from the descriptor and count header, then its size
 is reduced to 48 bits, which would seem to be as convenient to handle
 as the proposed 72 bit transaction header.
 Another source of difficulty lies in the implementation of the (the
 SEX time-sharing system) the 'end' of a file (which presumably would
 be the begin point of an Append transaction) is almost com- pletely
 context-defined--i.e., the program reading the file determines when
 it has reached the end of the file.  Therefore, the meaning of
 'Append' is somewhat hazy, and since the proposed Mail Box Protocol
 uses the Append feature, not implementing this command in a File
 Transfer service is costly in terms of lost useability.
 We believe that resolution of these ambiguities will lead to a
 greatly accelerated implementation schedule, at least here at UCLA-
     [ This RFC was put into machine readable form for entry ]
     [ into the online RFC archives by BBN Corp. under the   ]
     [ direction of Alex McKenzie.                   12/96   ]
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