CONTENTS

1 Scope
2 References
3 Definitions
3.1 Reference model definitions
3.2 Service conventions definitions
3.3 Network service definitions
3.4 X.25 definitions
3.5 APS definitions
4 Abbreviations
4.1 Reference model abbreviations
4.2 Network layer abbreviations
4.3 X.25 abbreviations
4.4 Data link layer abbreviations
4.5 Other abbreviations
5 Overview
5.1 Configurations
5.2 Modes of operation and their APS layers representation
5.2.1 V.42-dependent mode
5.2.2 LAPB mode
5.2.3 X.25 mode
5.2.4 Mode negotiations
5.2.5 Mode support
6 Provision of the OSI CONS
6.1 Control of underlying connections
6.2 Mapping OSI CONS to/from X.25 PLP
6.3 Mapping OSI CONS to/from the APS network protocol
7 APS layer 2 protocols
7.1 Introduction
7.2 Start/stop LAPB
7.3 APS data link protocol
7.3.1 Reception of incorrect frames
7.4 Transparency
7.5 APS layer 2 operation and establishment of the underlying connection
7.5.1 Point-to-Point configuration
7.5.1.1 Establishment of the underlying connection
7.5.1.2 Data link set-up
7.5.1.3 LAPB addressing
7.5.1.4 Time fill
7.5.2 PAD configuration
7.5.2.1 Establishment of the underlying connection
7.5.2.2 Data link set-up
7.5.2.3 LAPB addressing
7.5.2.4 Time fill
7.5.2.5 Mapping of APS layer 2 frames to packets
7.5.2.6 Exception conditions
7.5.3 Direct network configuration
7.5.3.1 Establishment of the underlying connection
7.5.3.2 LAPB data link set-up
7.5.3.3 LAPB addressing
7.5.3.4 Time fill
8 APS layer 3 protocols
8.1 The APS network protocol
8.1.1 APS network protocol elements of procedure
8.1.1.1 Connection establishment procedure
8.1.1.2 Data transfer procedure
8.1.1.3 Disconnect procedure
8.1.2 APS network protocol structure
8.1.2.1 The connect request PDU
8.1.2.2 The connect confirm PDU
8.1.2.3 The data transfer PDU
8.1.2.4 The disconnect request PDU
8.1.2.5 The disconnect confirm PDU
8.1.2.6 Maximum user data in APS NPDUs
8.2 X.25 PLP operation
8.2.1 Optional and negotiable parameters
8.2.1.1 Parameter usage in the Direct Network configuration
Annex A Transparency
A.0 Transparency
A.1 Introduction
A.2 APS PAD transparency
Annex B APS protocols selection string
B.0 APS protocols selection string
B.1 Introduction
B.2 APS protocols selection string format
B.3 Use of the call user data in X.25 call requests
Annex C Use of the APS network protocol to provide the OSI Connection-mode network service
C.0 Use of the APS network protocol to provide the OSI connection-mode network service
C.1 Introduction
C.2 Network connection establishment phase
C.3 Data transfer phase
C.3.1 Handling of NS-user-data
C.3.2 The reset service
C.4 Network connection release phase
C.4.1 Mapping of N-DISCONNECT Parameters
Annex D Recommended practices for use in MHS environment
D.0 Recommended practices
D.1 APS layer 3 protocols
D.1.1 Use of the APS network protocol for simultaneous communications
D.1.2 Handling of future versions
D.2 APS layer 2 protocols
D.2.1 LAPB retransmission timer
D.3 Start/stop framing
D.3.1 Fast Frame Control Check (FCS) implementation
D.4 Modems
D.4.1 V.42 modems
D.4.2 Modems with automatic data rate switching
D.4.3 Modem flow control
D.5 PAD operation
D.5.1 Recommended PAD parameters
D.5.2 Remote PAD parameters
D.6 Timers and counters
D.6.1 APS layer 2
D.6.2 APS layer 3