RFC102

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

                OUTPUT OF THE HOST/HOST PROTOCOL
                   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 53.

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
  change.

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 process.

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.

UNRESOLVED ALTERNATIVES

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 messages.

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:

             <------------16------------>
              __________________________
             |                          |
             |_ _ _ _  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.

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 ]