CONTENTS

RECOMMENDATION  ITU-R M.1798^,      2
Characteristics of HF radio equipment for the exchange of digital data and electronic mail in the maritime mobile service     2
Scope     2
Annex 1  Examples of HF maritime data services, characteristics  and modem protocols     4
1 Introduction  4
2 System interoperability  4
3 System 1 � HF data services modem protocol using orthogonal frequency division multiplexing (OFDM)     5
4 System 2 � Electronic mail system using Pactor-III protocol, including the system used by the Global Link Network (GLN)     39
        4.1 The PACTOR‑III protocol (Technical Description by Hans-Peter Helfert and Thomas Rink, SCS GmbH & Co. KG, Hanau, Germany)     40
                  4.1.1 Introduction  40
                  4.1.2 Speed levels (SLs) and bandwidth  40
                  4.1.3 Modulation, coding, and data rates  41
                  4.1.4 Crest factor (CF) and transmitter output power 43
                  4.1.5 Cycle duration  44
                  4.1.6 Structure of packets and control signals  44
                  4.1.7 Online data compression  45
                  4.1.8 Signal characteristics and practical considerations  47
                  4.1.9 Performance measurements  47
        4.2     Typical communication protocol (T‑BUS) 50
        4.3 Global Link Network (GLN) 51
Technical structure     52
NCC     52
CRS     52
Ship earth station (SES)     52
Internet     53
Interfacing     53
Data security     53
E‑mail service     54
Weather information service     54
Vessel tracking     54
Crew mail     54
Ship security alert system (SSAS)     54