rfc793.txt

RFC 相关的技术文档

RFC: 793
                                    
                                    
                                    
                                    
                                    
                                    
                                    
                     TRANSMISSION 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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[Page ii]                                                               


September 1981                                                          
                                           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




































                                                              [Page iii]




RFC:  793
Replaces: RFC 761
IENs:  129, 124, 112, 81,
55, 44, 40, 27, 21, 5

                     TRANSMISSION CONTROL PROTOCOL

                         DARPA INTERNET PROGRAM
                         PROTOCOL SPECIFICATION



                            1.  INTRODUCTION

The Transmission Control Protocol (TCP) is intended for use as a highly
reliable host-to-host protocol between hosts in packet-switched computer
communication networks, and in interconnected systems of such networks.

This document describes the functions to be performed by the
Transmission Control Protocol, the program that implements it, and its
interface to programs or users that require its services.

1.1.  Motivation

  Computer communication systems are playing an increasingly important
  role in military, government, and civilian environments.  This
  document focuses its attention primarily on military computer
  communication requirements, especially robustness in the presence of
  communication unreliability and availability in the presence of
  congestion, but many of these problems are found in the civilian and
  government sector as well.

  As strategic and tactical computer communication networks are
  developed and deployed, it is essential to provide means of
  interconnecting them and to provide standard interprocess
  communication protocols which can support a broad range of
  applications.  In anticipation of the need for such standards, the
  Deputy Undersecretary of Defense for Research and Engineering has
  declared the Transmission Control Protocol (TCP) described herein to
  be a basis for DoD-wide inter-process communication protocol
  standardization.

  TCP is a connection-oriented, end-to-end reliable protocol designed to
  fit into a layered hierarchy of protocols which support multi-network
  applications.  The TCP provides for reliable inter-process
  communication between pairs of processes in host computers attached to
  distinct but interconnected computer communication networks.  Very few
  assumptions are made as to the reliability of the communication
  protocols below the TCP layer.  TCP assumes it can obtain a simple,
  potentially unreliable datagram service from the lower level
  protocols.  In principle, the TCP should be able to operate above a
  wide spectrum of communication systems ranging from hard-wired
  connections to packet-switched or circuit-switched networks.


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                                                          September 1981
Transmission Control Protocol
Introduction



  TCP is based on concepts first described by Cerf and Kahn in [1].  The
  TCP fits into a layered protocol architecture just above a basic
  Internet Protocol [2] which provides a way for the TCP to send and
  receive variable-length segments of information enclosed in internet
  datagram "envelopes".  The internet datagram provides a means for
  addressing source and destination TCPs in different networks.  The
  internet protocol also deals with any fragmentation or reassembly of
  the TCP segments required to achieve transport and delivery through
  multiple networks and interconnecting gateways.  The internet protocol
  also carries information on the precedence, security classification
  and compartmentation of the TCP segments, so this information can be
  communicated end-to-end across multiple networks.

                           Protocol Layering

                        +---------------------+
                        |     higher-level    |
                        +---------------------+
                        |        TCP          |
                        +---------------------+
                        |  internet protocol  |
                        +---------------------+
                        |communication network|
                        +---------------------+

                                Figure 1

  Much of this document is written in the context of TCP implementations
  which are co-resident with higher level protocols in the host
  computer.  Some computer systems will be connected to networks via
  front-end computers which house the TCP and internet protocol layers,
  as well as network specific software.  The TCP specification describes
  an interface to the higher level protocols which appears to be
  implementable even for the front-end case, as long as a suitable
  host-to-front end protocol is implemented.

1.2.  Scope

  The TCP is intended to provide a reliable process-to-process
  communication service in a multinetwork environment.  The TCP is
  intended to be a host-to-host protocol in common use in multiple
  networks.

1.3.  About this Document

  This document represents a specification of the behavior required of
  any TCP implementation, both in its interactions with higher level
  protocols and in its interactions with other TCPs.  The rest of this


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September 1981                                                          
                                           Transmission Control Protocol
                                                            Introduction



  section offers a very brief view of the protocol interfaces and
  operation.  Section 2 summarizes the philosophical basis for the TCP
  design.  Section 3 offers both a detailed description of the actions
  required of TCP when various events occur (arrival of new segments,
  user calls, errors, etc.) and the details of the formats of TCP
  segments.

1.4.  Interfaces

  The TCP interfaces on one side to user or application processes and on
  the other side to a lower level protocol such as Internet Protocol.

  The interface between an application process and the TCP is
  illustrated in reasonable detail.  This interface consists of a set of