Host Software (RFC0001)

Network Working Group                                   Steve Crocker

Request for Comments: 1                                          UCLA

                                                         7 April 1969

                         Title:   Host Software

                        Author:   Steve Crocker

                          Installation:   UCLA

                          Date:   7 April 1969

             Network Working Group Request for Comment:   1

CONTENTS

INTRODUCTION

  I. A Summary of the IMP Software

     Messages

     Links

     IMP Transmission and Error Checking

     Open Questions on the IMP Software

 II. Some Requirements Upon the Host-to-Host Software

     Simple Use

     Deep Use

     Error Checking

III. The Host Software

     Establishment of a Connection

     High Volume Transmission

     A Summary of Primitives

     Error Checking

     Closer Interaction

     Open Questions

Crocker                                                        [Page 1]

RFC 1                        Host Software                 7 April 1969

 IV. Initial Experiments

     Experiment One

     Experiment Two

Introduction

   The software for the ARPA Network exists partly in the IMPs and

   partly in the respective HOSTs.  BB&N has specified the software of

   the IMPs and it is the responsibility of the HOST groups to agree on

   HOST software.

   During the summer of 1968, representatives from the initial four

   sites met several times to discuss the HOST software and initial

   experiments on the network.  There emerged from these meetings a

   working group of three, Steve Carr from Utah, Jeff Rulifson from SRI,

   and Steve Crocker of UCLA, who met during the fall and winter.  The

   most recent meeting was in the last week of March in Utah.  Also

   present was Bill Duvall of SRI who has recently started working with

   Jeff Rulifson.

   Somewhat independently, Gerard DeLoche of UCLA has been working on

   the HOST-IMP interface.

   I present here some of the tentative agreements reached and some of

   the open questions encountered.  Very little of what is here is firm

   and reactions are expected.

I.   A Summary of the IMP Software

Messages

   Information is transmitted from HOST to HOST in bundles called

   messages.  A message is any stream of not more than 8080 bits,

   together with its header.  The header is 16 bits and contains the

   following information:

           Destination     5 bits

           Link            8 bits

           Trace           1 bit

           Spare           2 bits

   The destination is the numerical code for the HOST to which the

   message should be sent.  The trace bit signals the IMPs to record

   status information about the message and send the information back to

   the NMC (Network Measurement Center, i.e., UCLA).  The spare bits are

   unused.

Crocker                                                        [Page 2]

RFC 1                        Host Software                 7 April 1969

Links

   The link field is a special device used by the IMPs to limit certain

   kinds of congestion.  They function as follows.  Between every pair of

   HOSTs there are 32 logical full-duplex connections over which messages

   may be passed in either direction.  The IMPs place the restriction on

   these links that no HOST can send two successive messages over the

   same link before the IMP at the destination has sent back a special

   message called an RFNM (Request for Next Message).  This arrangement

   limits the congestion one HOST can cause another if the sending HOST

   is attempting to send too much over one link.  We note, however, that

   since the IMP at the destination does not have enough capacity to

   handle all 32 link...