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Network Working Group Steve Crocker, Chairman Request for Comments: 102 at BBN, Cambridge NIC#5763 22, 23 February 1971

                     GLITCH CLEANING COMMITTEE
 At the NWG meeting in Urbana on 17-19 February 1971, a
 committee was established to look at the Host/Host protocol
 and see what changes were immediately desirable or necessary.
 The committee is chaired by Steve Crocker, and has eight
 other members:
           Ray Tomlinson                 BBN (Tenex)
           Jim White                     UCSB
           Gary Grossman                 Illinois
           Tom Barkalow                  Lincoln (TX2)
           Will Crowther                 BBN (IMPs)
           Bob Bressler                  MIT (Dynamic Modeling
           Doug McKay                    IBM (Yorktown)
           Dan Murphy                    BBN (Tenex)
 A number of topics were discussed.  On some of these topics, a
 consensus was reached on whether or not to recommend a change, and if
 so, what the change should be.  On the remaining topics, specific
 alternatives were proposed but no consensus was reached.
 The committee will immediately canvas the network community and
 gather reaction to its recommendations and the proposed alternatives.
 The committee will then reconvene at UCLA on 8 March 1971 and decide
 on final recommendations.  Steve Crocker will then write Document #2.
 This sequence is in lieu of the change procedure outlined in NWG/RFC


 Specific Recommendations
 1. The ECO and ERP command should each be 8 bits long.
 2. The ERR command should be 96 bits long.
 3. Message Data Types should be eliminated.  Third-level protocol
    people may reinstate such a mechanism.
 4. The Cease mechanism should be discontinued.
 5. A new pair of one byte commands RST (reset) and RRP (reset reply)
    should be added.  The RST should be interpreted as a signal to
    purge the NCP tables of any existing entries which arose from the
    sending Host.  The RRP command should be returned to acknowledge
    receipt of the RST.  The Host sending the RST may proceed after
    receiving either a RST or a RRP in return.  A RST may be returned
    if the second Host comes up after the first Host.
 6. Although it was suggested at the Urbana meeting that connections
    should be full-duplex, the committee recommends against this
 7. Messages should be an integral number of bytes, and the number of
    bytes and the byte size should be specified in each message.  The
    marking convention should be abandoned and the padding ignored.
    The number of bytes in the message should be a 16-bit number
    following the leader.  The byte size should be in the next 8-bit
    field.  Two suggestions were generated for the starting point of
    the text, and these are explained in the next session.
    For flow control purposes, the number of bits in a message is the
    product of the number of bytes and the byte size.  The leader and
    other fixed format fields are not counted.
 8. The problem of synchronizing the interrupt signal in a console
    input stream was considered.  We consider the console input
    scanner as a process and note two reasonable implementations: it
    may either read characters as fast as it can, looking for the
    interrupt character and throwing away characters if there is no
    room in the user process' input queue; it may read characters only
    as fast as the user process can receive them, (or at least has
    room for them).
 The first implementation guarantees that the interrupt character
 (e.g., control - C on the PDP-10 10/50) will always be acted on, but
 requires that the using process interpret the output stream to detect


 when it is sending too fast.  The second implementation avoids
 overrun but may not allow for sending an interrupt code.  Note that
 in the first case, allocation is alway renewed as soon as possible by
 the console input interpreter; whereas in the second case, allocation
 is renewed only as the result of acceptance of data by the user
 We decided that this is really a third-level protocol matter, viz,
 use the INS to mean that a special code has been inserted into the
 input stream.  In conjunction with this, create the special code to
 be put into the input sequence.
 This special code would be network-wide and independent of the
 particular interrupt character peculiar to the serving system.  The
 scheme for interrupting a serving process is that the using process
 inserts the serving Host's interrupt sequence, followed by the
 network special code, and also issue the INS.


 1. Length of Control Messages
 In accordance with other specifications, control messages should be
 an integral number of 8-bit bytes, the length should be specified in
 the byte count field, and control commands should not be split across
 Unresolved was whether to specially limit the length of control
 messages.  The two choices are.
    a) no special limit ( ~ 1000 bytes)
    b) 120 bytes
 2. Message Format
 It was agreed to abandon marking and include the text length in the
 form of a byte count and byte size.  Unresolved was where to begin
 the first byte of data.  The two choices are:
    a) have the first data byte begin after 72 bits of leader, byte
    count, byte size and spacing.  The message format would then be as
    in the diagram:


               |                          |
               |_ _ _ _  LEADER   _ _ _ _ |
               |                          |
               |                          |
               |        BYTE COUNT        |
               |            |             |
 BYTE SIZE-----|---->       |             |
               |            |             |
               |            |<------------|--Beginning of first
               |____________|_____________|       data byte
               |                          |
               |                          |
    b) use the double physical transmission scheme presented in
    NWG/RFC 67.  When sending a regular message, the Host would send a
    leader, byte count and byte size and terminate transmission.  The
    second transmission would be the data.
    At the receiving end, the IMP would transmit 64 bits of leader,
    byte count, byte size and spacing, and stop transmission.  The
    next transmission would be only the data.

3. Allocation

 With respect to the allocation mechanism embodied in the ALL, GVB and
 RET commands, two alternatives were proposed:
    a) make no change.
    b) The flow control algorithm should be changed to keep track of
    two quantities: messages and bits.  The ALL, GVB, and RET commands
    each have two data fields.  The ALL command allocates a message
    limit and a bit limit.  The GVB command contains two fractions,
    and the RET command returns both messages and bits.  When sending
    a message, the sending NCP decrements its message counter by 1 and
    its bit counter by the text length of the message.  The sending
    NCP may not cause either of its counters to go negative.  The
    message counter would be 16 bits long.
       [ This RFC was put into machine readable form for entry ]
       [ into the online RFC archives by Gottfried Janik 02/98 ]

Crocker [Page 4]

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