PSBNSMISSION CONTROL PROTOCOL
                         DARPA INTERNET PROGRAM
                         PROTOCOL SPECIFICATION
                                    
                             September 1981

                              prepared for
                                    
               Defense Advanced Research Projects Agency
                Information Processing Techniques Office
                         1400 Wilson Boulevard
                       Arlington, Virginia  22209

                                   by

                     Information Sciences Institute
                   University of Southern California
                           4676 Admiralty Way
                   Marina del Rey, California  90291

September 1981                                                          
                                           Transmission Control Protocol

                           TABLE OF CONTENTS

    PREFACE ........................................................ iii

1.  INTRODUCTION ..................................................... 1

  1.1  Motivation .................................................... 1
  1.2  Scope ......................................................... 2
  1.3  About This Document ........................................... 2
  1.4  Interfaces .................................................... 3
  1.5  Operation ..................................................... 3

2.  PHILOSOPHY ....................................................... 7

  2.1  Elements of the Internetwork System ........................... 7
  2.2  Model of Operation ............................................ 7
  2.3  The Host Environment .......................................... 8
  2.4  Interfaces .................................................... 9
  2.5  Relation to Other Protocols ................................... 9
  2.6  Reliable Communication ........................................ 9
  2.7  Connection Establishment and Clearing ........................ 10
  2.8  Data Communication ........................................... 12
  2.9  Precedence and Security ...................................... 13
  2.10 Robustness Principle ......................................... 13

3.  FUNCTIONAL SPECIFICATION ........................................ 15

  3.1  Header Format ................................................ 15
  3.2  Terminology .................................................. 19
  3.3  Sequence Numbers ............................................. 24
  3.4  Establishing a connection .................................... 30
  3.5  Closing a Connection ......................................... 37
  3.6  Precedence and Security ...................................... 40
  3.7  Data Communication ........................................... 40
  3.8  Interfaces ................................................... 44
  3.9  Event Processing ............................................. 52

GLOSSARY ............................................................ 79

REFERENCES .......................................................... 85











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                                           Transmission Control Protocol



                                PREFACE



This document describes the DoD Standard Transmission Control Protocol
(TCP).  There have been nine earlier editions of the ARPA TCP
specification on which this standard is based, and the present text
draws heavily from them.  There have been many contributors to this work
both in terms of concepts and in terms of text.  This edition clarifies
several details and removes the end-of-letter buffer-size adjustments,
and redescribes the letter mechanism as a push function.

                                                           Jon Postel

                                                           Editor