Introduction to Tandem X.25 Capabilities

Contents

065307 Tandem Computers Incorporated iii

Preface ix

Section 1 What is X.25?

Multi-Vendor International Communications Protocol 1-1

Benefits of X.25 1-1

Need for a Common Standard 1-1

Comparing X.25 with other Networking Standards 1-4

Using X.25 for Direct Connections 1-5

PAD-Related Standards 1-6

PAD 1-6

Internetwork Related Standards 1-9

Addressing in X.25 Networks 1-10

Port Numbers or Subaddressing 1-10

X.25 Layers 1-11

Packet-Layer Components 1-12

Routing 1-13

Packet Structure 1-15

Packet Types 1-19

Call Setup Packets 1-19

Call-Clear Packets 1-20

Data Packets 1-21

Interrupt Packets 1-23

Flow-Control Packets 1-23

Reset Packets 1-23

Restart Packets 1-23

Diagnostic Packets 1-23

Data-Link-Layer Components 1-24

LAP 1-24

LAPB 1-24

Frame Structure 1-26

Frame Types 1-31

I-Frames 1-31

S-Frames 1-31

U-Frames 1-33

Physical-Layer Components 1-35

X.21 bis 1-35

X.21 1-36