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Network Working Group R. T. Braden Request for Comments #238 UCLA-CCN NIC #7663 September 29, 1971 Category: Updates: RFC #171, RFC #172

 Data Transfer Protocol
 1. In the Descriptor/Count mode, the Information Separators should
 have a transaction sequence number field.  Otherwise, the receiver
 cannot be sure he received all transactions before the separation.
 This requires that there be two forms of information separators, one
 for Descriptor/Count mode, the other for the DLE mode.
 2. The modes-available handshake should not be mandatory, as it makes
 no sense in the simplex case.  The receiver doesn't care what modes
 the transmitter _might_ use; he only cares what mode _is_ used, which
 he discovers when the first data or control transaction arrives.  Even
 in the duplex case, it is not clear what use the receiver should make
 of the modes-available information from the transmitter.
 File Transfer Protocol
 1. The protocol allows an end-of-file to be indicated by closing the
 connection.  This is the same mistake which we made in an early
 version of NETRJS.  Closing the connection without a File Separator
 transaction should only be used to indicate an error, i.e., to abort
 the transmission; it should never be used to indicate normal
 completion of file transfer.  The reason is obvious: there is no way
 for the receiver to tell whether CLS indicates normal completion or an
 abnormal condition in the other host (e.g. the file transfer program
 2. There should be two forms of the _store_ request, one which fails
 if a file of the same name already exists, and one which replaces an
 existing file of the same name (as now).
 3. A service center host may be expected to require username and
 password transactions before any others are accepted.
 4. There are no error transactions defined for lost data or lost
 synch.  It is assumed there are handled at the DTP level?
 5. All of the defined error codes should be allowed (and encouraged)
 to have explanatory text following them.
                                                              [Page 1]


     [ 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   ]
                                                              [Page 2]
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