CONTENTS

  Title Page

  Copyright Page

  Preface

  1      The Principles of Packet Switching and X.25

  1.1     What Is X.25?

  1.2     Packet Switching Communications
    1.2.1      Types of DTE

  1.3     PADs and Character-Mode Terminals

  1.4     X.25 in Detail
    1.4.1      Packet Level
    1.4.2      Frame Level
    1.4.3      Physical Level

  1.5     Other Standards Relevant to X.25
    1.5.1      The International Standards Organization (ISO)

  2      Specific Operation of PSDNs

  2.1     Physical Connections

  2.2     Logical Connections
    2.2.1      Virtual Circuits
    2.2.2      Logical Channel Numbers

  2.3     DTE Addresses

  2.4     Controlling the Flow of Packets

  2.5     The Optional Facilities of Public and Private PSDNs
    2.5.1      Closed User Groups
    2.5.2      Bilateral Closed User Groups
    2.5.3      PAD Parameters
    2.5.4      DTE System Parameters

  3      Digital's X.25 Products

  3.1     VAX P.S.I.
    3.1.1      VAX P.S.I. Native
    3.1.2      VAX P.S.I. Multihost
    3.1.3      VAX P.S.I. Access
    3.1.4      Combination Systems
    3.1.5      X.29 Terminals
    3.1.6      DECnet Communications
    3.1.7      LLC2 Communications

  3.2     DEC X25gateway 100/500
    3.2.1      Connector System
    3.2.2      Portal Mode
    3.2.3      CONS LAN/WAN Relay

  3.3     DEC WANrouter 100/500

  4      Additional Features of Some of Digital's X.25 Products

  4.1     P.S.I. MAIL

  4.2     X.25 and X.29 Programming

  4.3     VAX P.S.I. Accounting

  4.4     Securing Your X.25 System

  4.5     PSDN Support

  A   General Optional Facilities Supported by PSDNs

  B   Optional Facilities of CUGs and BCUGs

  C   Optional PAD Facilities

  D   DTE System Parameters

  E   Documentation for Digital's X.25 Products

  Glossary

  FIGURES

  1-1        Individual Packets Travelling over a PSDN

  1-2        The Equipment Involved in Packet Switching

  1-3        Connecting Character-Mode DTEs to a PSDN

  1-4        The X.25 Protocol Levels

  1-5        The Structure of a Frame

  1-6        The CCITT X Series of Recommendations

  2-1        An Example DTE Address

  3-1        VAX P.S.I. Native

  3-2        Connecting Access Nodes to PSDNs

  3-3        A Combination System

  3-4        LLC2 Communications

  3-5        DEC X25gateway used as a Connector System

  3-6        DEC X25gateway in Portal Mode

  3-7        A CONS LAN/WAN Relay

  3-8        The X.25 Function of the DEC WANrouter

  TABLES

  A-1        Optional User Facilities Supported by PSDNs

  B-1        Optional Facilities Related to CUGs

  B-2        Optional Facilities Related to BCUGs

  C-1        PAD Parameters

  D-1        Packet Control Parameters

  D-2        Frame Control Parameters