    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-
       NMC.

           [ 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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