    Network Working Group                          A. Bhushan, MIT
    Request for Comments #176                      R. Kanodia, MIT
    NIC #7100                                      R. Metcalfe, MIT
    Categories: C and D                            J. Postel, UCLA
                                                   14 June 1971

                     Comments on Byte Size for Connections
                     -------------------------------------

         There are at least the following three views on the use of
    byte size for network connections*:

         1)   Byte size should not be used at all.

         2)   Byte size is solely for the convenience of NCP's.

         3)   Byte size choice is a user-level prerogative.

         According to the first view, network connections are bit
    streams, and messages should contain bit counts (i.e., a
    byte size of 1).  This view existed before the "Glitch Cleaning"
    of RFC 107, and was discarded in favour of byte stream because
    of stated reasons of efficiency in storage management and
    message concatenation.

         The second view represents a special interpretation of
    RFC 107.  According to this interpretation, byte size is
    entirely a 2nd level (i.e., NCP) issue.  There is no require-
    ment that 3rd level user processes be able to specify byte size.
    This view is indicated in RFC 151 by Shoshani.

    ----------------------
    * Byte size for connection is the byte size selected by
    sending NCP, as explained in RFC 107 (Output of Host-Host
    Protocol Glitch Cleaning Committee).

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    RFC #176                        -2-                   NIC #7100

         According to the third view user processes are always
    allowed to choose byte size for connection, either explicitly
    (specify a specific byte size parameter) or implicitly (byte
    size depends on I/O mode).  An NCP is allowed to use a default
    byte size, if the user does not specify it.

                                The Correct View
                                ________________

         The third view should be considered the correct interpre-
    tation of RFC 107.  In fact, RFC 107 states on page 2, "the
    choice of the byte size for a connection is a 3rd level protocol
    issue."   To be consistent with TELNET, ICP, and other 3rd
    level protocols which require that a specific byte size be
    used for connection, it is imperative that corresponding 3rd
    level processes be able to specify (and_impose) a particular
    byte size to the NCP.  NCP implementors should take note of it.

             On Specifying Fixed Byte Sizes in 3rd Level Protocols
             -----------------------------------------------------

         Holding the view that byte size choice is a 3rd level
    issue, we are still faced with the following two questions.
    First, is it appropriate for 3rd level protocols to legislate
    a specific byte size for all connections using that protocol?
    Second, if it is appropriate to specify byte size, then what
    should this choice be?

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    RFC #176                        -3-                   NIC #7100

         There are two arguments in favour of using specific
    byte size in 3rd level protocols.  First is that a potential
    mismatch problem exists because RFC 107 does not require
    that NCPs be capable of handling all byte sizes 1 through 255.
    Using a fixed byte size of 8-bits or 8-bit multiples resolves
    the problem as this is acceptable to all hosts (including
    terminal IMPs).

         The second argument is one of efficiency.  If it is agreed
    before hand that only a specific byte size would be used,
    it is possible to make programs more efficient (i.e., reduce
    program space, and possibly run time).  The efficiency argument
    assumes that the byte size for connection represents the natural
    byte structure of data being transferred over the connection.

         For TELNET and ICP, the byte size choice is straight
    forward as data is naturally in 8-bit multiples (8-bit ASCII
    characters in TELNET, and 32-bit socket numbers in ICP).  But
    for data transfer protocols, the byte size choice is more complex,
    as data may be structured in a variety of byte sizes.  Specifying
    a byte size for a data transfer connection reduces efficiency
    in instances where connection byte size does not correspond
    to data byte size.  Further, filler fields will be required
    for data blocks which are not a multiple of the fixed byte
    size.  This imposes an additional overhead.

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    RFC #176                        -4-                   NIC #7100

         Even if all hosts were to accept arbitrary byte sizes,
    and the 3rd level protocol does not legislate a specific byte
    size, the inefficiency problem will not be solved entirely.
    Under current specifications "the byte size is fixed for the
    life of a connection".*  This means that byte size cannot be
    varied during the life of a connection even if structure of
    data varies.  The problem of inefficiency is solved only for
    instances in which data has a constant byte structure.

         Given the current state of the network, it appears that
    specifying fixed byte size in 3rd level protocols is a good
    idea.  This eliminates the potential byte size mismatch problem,
    and improves efficiency at least for TELNET and ICP.  In data
    transfer, the efficiency issue is more complex, as discussed
    earlier.  It is not clear that overall efficiency would be
    degraded if a fixed byte size was required.

                        On Reopening the Byte Size Issue
                        --------------------------------

         The above discussion exposes certain weaknesses in the
    efficiency arguments for having byte streams on network connec-
    tions.  In moving from bit stream to byte stream, we may have
    lost generality, and it is not clear how much overall efficiency
    is gained.  Sometimes, the gain in NCP efficiency may be at the
    expense of user process efficiencies.

    --------------------

    *    RFC 107, page 2

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    RFC #176                        -5-                   NIC #7100

         It is also clear that for efficiency arguments to hold,
    the byte size choice should not be an NCP prerogative.  It
    is the combined efficiency, rather than NCP efficiency which
    should be our primary concern.  Restricting byte size choice
    to NCPs has the further disadvantage of potential byte size
    mismatch not only between communicating NPCs but also at the
    user-NCP interface.  Therefore, allowing a user process to
    specify byte size is a step in the right direction, given
    that we have adopted byte streams.

         It is our opinion that the issue of bit stream and byte
    stream be set aside until serious consideration can be given
    to a major Host-Host Protocol overhaul.  At a later stage
    we will have a better idea of the relative efficiency merits.

           [ 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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