Inmarsat ses

Inmarsat
Maritime Communications
Handbook
Issue 2

International Maritime Satellite Organization (Inmarsat)
Maritime Services Division
99 City Road
London EC1 Y lAX

u.K.
Telephone: +44 171 728 1000 (Switchboard)
Fax: +44 171 728 1752
Telex: 297201 INMSAT G


Inmarsat
Maritime Communications Handbook

Contents
Foreword
Preface
Chapter 1

The Inmarsat Satellite Communications Systems

Chapter 2

Inmarsat Distress & Safety Services

Chapter 3

Inmarsat SES Commissioning Procedures

Chapter 4

Inmarsat Traffic Accounting and Billing Arrangements

Chapter 5

Your Inmarsat-A Ship Earth Station

Chapter 6

Your Inmarsat-C Ship Earth Station

Chapter 7

Your Inmarsat-M and Inmarsat-B Ship Earth Station

Chapter 8

Using Inmarsat in the shore-to-ship direction

Appendix A

Inmarsat Maritime Customer Services

Appendix B

List of SES manufacturers

Appendix C

How to point your Antenna

Appendix 0

2-digit Code Services (Telex and Telephone) and Fault Codes

Appendix E

The Inmarsat Coast Earth Stations

Appendix F

International telephone Country Codes

Appendix G

International telex Country Codes

Appendix H

Glossary

Appendix I

Publications Registration Form & Comment Sheet

Foreword
by Captain Lars Brodje,
Maritime Adviser to the International Maritime Satellite Organization

When the first issue of this Handbook was published, in February 1994, the intention was
primarily to provide a textbook for maritime colleges and other maritime training institutions
to use in tuition and training for the General Operator's Certificate (GOC), as required in the
Global Maritime Distress and Safety System (GMDSS).
It was also thought that the handbook might be used for reference on Inmarsat-equipped
vessels, in conjunction with manufacturer's manuals for specific Inmarsat Ship Earth Stations
(SES's).
Almost a year, and ten thousand copies later, we are now convinced about the usefulness of
an Inmarsat Maritime Communications Handbook, both to support tuition about maritime
communication and as a handbook aboard Inmarsat-equipped vessels.
The present version of the handbook has been extensively updated and contains a new and
comprehensive chapter about the Inmarsat-B service which will have its global launch during
1995.
Like the first version of the handbook, this version has been developed by a group of Inmarsat
staff, with maritime backgrounds, now mainly occupied in customer support functions. In the
development of this version we have also been able to include a range of invaluable comments
and suggestions from users of Inmarsat terminals around the world.
Additional information, such as country codes for telephone/telex, Coast Earth Station (CES)
operators and Ship Earth Station (SES) manufacturers, is also included, together with a
glossary explaining many of the abbreviations commonly used in the field of maritime satellite
communication.
In our continued efforts to serve the international maritime community we are pleased to
receive comments and suggestions on how to increase the value of this handbook to the user.
Additional handbooks and further information about Inmarsat services and applications may
be received, free of charge, by filling in and mailing the last two pages of the handbook to

Inmarsat.
London, January 1995
Inmarsat Maritime Services Division


PREFACE
The structure of this handbook
Chapter 1 introduces Inmarsat and its major components, and explains in simple terms how
calls are routed between a Ship Earth Station (SES) and subscribers to the public
telecommunications networks. This chapter also describes the main features of the current
Inmarsat-A, Inmarsat-C, Inmarsat-M and Inmarsat-B systems.
Chapter 2 explains the role of Inmarsat in the Global Distress and Safety System (GMDSS),
and tells you the main features of the Inmarsat-E distress alerting system.
Chapter 3 is an introduction to commissioning, the process which every new SES must
complete before Inmarsat will permit it to access any Inmarsat system.
Chapter 4 explains the Inmarsat accounting, billing and settlement process, for ship-to-shore
calls and shore-to-ship calls.
Chapters 5, 6 and 7 summarize the operating features of Inmarsat -A, Inmarsat -C and
Inmarsat-M and B SESs respectively.
Chapter 8 describes the use of the Inmarsat systems in the shore-to-ship direction.
The Appendices at the rear of the book provide you with additional information that you may
need to know about Inmarsat or its systems.

Type-approved SES models and generic information
The Inmarsat organization does not manufacture SES models, but permits independent
manufacturers to submit their designs to Inmarsat, to confirm that they meet defined technical
standards. Only models that meet these standards are granted formal type-approval by
Inmarsat. The information in this manual is not specific to any particular type-approved SES
model, but is generic in nature. For specific information on a particular model, you are
referred to the manufacturer's information.

Getting help
You may obtain help from the following sources:
For help on the Inmarsat-A, Inmarsat-C or Inmarsat-M and B systems:, contact the
relevant Inmarsat Maritime Customer Relations Officer at the address given in Appendix A.
For help on your Inmarsat SES: If you have any problems specific to your SES model,
or want to find out about upgrades or new features for your model, contact the agent who
supplied the SES, or the manufacturer, at the address given in Appendix B.
For help on CES services, charges and technical matters, enquire via the CES
Customer Contact, at the numbers given in Appendix E.

The Inmarsat Help-lines
Inmarsat provides "Help-lines" which can be accessed using either telex equipment or a
personal computer/modem combination. The Help-lines provide help facilities, including
information retrieval, mailbox facilities and a database facility to find the IMN (Inmarsat
Mobile Number) for a particular vessel.


Access to the Telex Help-line is open to anyone with telex equipment connected to the
international telex network, by calling the telex number:
(51) 920327 INMHLP G
where 51 is the Country Code for the UK, and 920327 INMHLP G is the number of the Telex
Help-line in the Inmarsat Headquarters in London, UK.
Follow the on-screen instructions to use the facility. In case of difficulty, down-load the HELP
information using the Main Menu.
Access to the Inmarsat Bulletin Board Service (BBS) is by means of a personal computer
and modem set-up, and the international telephone network. The modem should be Hayescompatible, set to 8 data bits, I stop bit, No Parity. The maximum speed of the Inmarsat BBS
is 9600 bps. The BBS is accessed by calling the international telephone number:
+44 171 728 1571
Information may be obtained either by file down-load, or listing. You can also use the BBS

to upload files to Inmarsat, and obtain the IMN (Inmarsat Mobile Number) for any particular
vessel. To become a registered user on the Inmarsat BBS call the number indicated above.
When connected to the BBS, type NEW and then follow on screen instructions to become
a registered user. You will be automatically disconnected after entering your details and there
will be a delay of 1 working day for entering your details into the computer at Inmarsat. After
that you should be able to access all of the BBS. Please remember to write down your
password and log-in name and store in a secure place. Inmarsat does not advise passwords and
if lost you will have to re-register.
For current information on the Inmarsat Help-lines, contact Inmarsat Customer Services at the
address given in Appendix A.

Other Inmarsat publications
Inmarsat produces a wide range of factsheets and information, as shown in Appendix I. To
obtain a copy of any of these publications, contact any of the Inmarsat Customer Relations
Officers at the address given in Appendix A.

A request for feedback
If you have any comments on this book, or consider that some information is incorrect, or
should be included, please let us know . We have provided a Comments Sheet in Appendix I
please cut out or copy the sheet, and return it with your comments to any of the Customer
Relations Officers at the address given in Appendix A.


Chapter 1
The Inmarsat Satellite Communications Systems

Contents
Page

1.1

1.2
1.3
1.4
1.5
1.6
1.7

Introduction
1.1.1 The Space Segment
1.1.2 The Ground Segment
1.1.3 The Ship Earth Stations
The Inmarsat-A system
1.2.1 Single-channel and multi-channel SESs
The new systems use new technology
The Inmarsat-C system
1.4.1 The Inmarsat-C system is part of the GMDSS
The Inmarsat-M system
The Inmarsat-B system
Using Inmarsat in the shore-to-ship direction

1-1
1-1
, 1-2
1-4
1-5
1-5
1-6
, 1-6
1-7

1-7
1-8
1-8

Figures
Figure 1-1
Figure 1-2
Figure
Figure
Figure
Figure
Figure

1-3
1-4
1-5
1-6
1-7

Inmarsat satellite being launched into geostationary orbit
View of the Inmarsat satellites in geostationary orbit
above the four Ocean Regions
Setting-up a communications channel for a ship-to-shore call
Comparative sizes and services of the different Inmarsat systems
Typical Inmarsat-A SES installation
Typical Inmarsat-C SES installation
Typical Inmarsat-M SES installation

1-1
1-2

1-3
1-4
1-5
1-6
1-8


Chapter 1

The Inmarsat Satellite Communications Systems

1.1 Introduction
Inmarsat (the International Maritime Satellite Organization) is a Partnership of member
countries, at present numbering 75 and growing. These countries co-operate to provide global
communications to and from ships (as well as portable/transportables, land-based vehicles and
aircraft) travelling anywhere within the four Ocean Regions (these are explained later).
The Inmarsat communications structure comprises three major components:
• The Space Segment.
• The Ground Segment.
• The Ship Earth Stations (SESs), Land-mobile Earth Stations (LMESs), and Aircraft Earth
Stations (AESs).

The Space Segment is
provided by Inmarsat, and
consists
of
four
communications satellites,
with backup satellites in
orbit, ready to be used if

necessary.
Each
satellite
was
launched by a powerful
rocket,
like
that
in
Figure
1-1,
into
a
geostationary
orbit
in
space. In this orbit, each
satellite moves at exactly
the same rate as the
rotation of the earth, and
so remains in the same
relative position to the
earth, above the earth's
equator. In this position,
antennas on the earth can
maintain communications
with the satellite.
The satellite's solar panels
provide it with electrical
power to perform

its
functions.
The Inmarsat satellites are
controlled
from
the
Satellite Control Centre
(SCC)
based
in
the
Inmarsat Headquarters in
London, UK.


TheInmarsatSatelliteCommunicationsSystems

Chapter 1

Each satellite has a coverage area (also known as its footprint), which is defined as the area
on the earth's surface (sea and/or land) within which a mobile or fixed antenna can obtain
line-of-sight communications with the satellite. Figure 1-2 shows the four satellites in space,
and their coverage areas, corresponding to the four Ocean Regions:
•
Atlantic Ocean Region-East (AOR-East).
•
Atlantic Ocean Region-West (AOR-West).
•
Indian Ocean Region (lOR).
•

Pacific Ocean Region (POR).

1.1.2

The Ground Segment

The Ground Segment comprises a global network of Coast Earth Stations (CESs), Network
Coordination Stations (NCSs), and a Network Operations Centre (NOC).
Each CES provides a link between the satellites and the
national/international
telecommunications networks. The large antennas used by the CESs to communicate with the
satellite for its Ocean Region are capable of handling many calls simultaneously to and from
the SESs.


Chapter 1

The Inmarsat Satellite Communications Systems

A CES Operator is typically a large telecommunications company, which can provide a wide
range of communications services to the SESs communicating through the CES.
Each of the Inmarsat communications systems has its own network of CESs, as below:
•
The Inmarsat-A CESs, shown in the map at the beginning of Chapter 5.
•
The Inmarsat-C CESs, shown in the map at the beginning of Chapter 6.
•
The Inmarsat-M and B CESs, shown in the map at the beginning of Chapter 7.
Table E-l in Appendix E shows the Ocean Region(s) in which the CESs operate.
For each Inmarsat system a Network Coordination Station (NCS) is located within each Ocean

Region, to monitor and control the communications traffic within its Ocean Region. Each NCS
communicates with the CESs in its Ocean Region, and with the other NCSs, as well as with
the Network Operations Centre (NOC) located in the Inmarsat Headquarters, making possible
the transfer of information throughout the system.
The NCSs are involved in setting-up calls to and from SESs. Figure 1-3 illustrates in general
terms how the NCS responds to a request from an SES for a communications channel, by
assigning a channel to which both the SES and CES are to tune for the call. A detailed
explanation for each Inmarsat system is given in Chapters 5, 6 and 7.




Chapter 1

The Inmarsat Satellite Communications Systems

1.2 The Inmarsat-A system
This was the first Inmarsat system, introduced into commercial operation in 1982, and now
providing two-way telephone, telex, fax, electronic mail (E-mail), and other forms of data
communications, including high-speed data (at 56 and 64 kilobits/sec). Recent developments
in data compression techniques enable the transmission of high-definition still photographs,
and even slow-scan video, to and from an Inmarsat-A SES.
The large size and weight of the Inmarsat-A antenna, as shown on Figure 1-4, has meant that
Inmarsat-A SESs have generally been fitted on larger ships such as oil tankers, trading vessels
and super-yachts. Figure 1-5 shows a typical Inmarsat-A maritime mobile installation. The
total number of maritime Inmarsat -A terminals in use all over the world was over 17,000 at
the start of 1995, and continues to grow.

1.2.1

Single-channel and multi-channel SESs

Inmarsat-A SESs can be purchased as either single-channel or multi-channel models, defined
as below:

Single-channel SES:
A single-channel SES is capable of using anyone of its communications services (for
example telephone, telex, fax or data) at a time, but not more than one service at the same
time.

Multi-channel SES:
A multi-channel SES is capable of using more than one service on different channels at
the same time - for example one channel can be making a telephone call, while, at the
same time, another channel can be receiving a fax.
Multi-channel operation could be useful for example on a cruise liner, to provide
independent telephone extensions, separately billable, for passenger use.


The Inmarsat Satellite Communications Systems

Chapter 1

1.3 The new systems use new technology
Developments in communications technology, particularly in digital technology, since the
introduction of the Inmarsat-A system in the 1970s allow more efficient use of the resources
of power and bandwidth, in the satellites, CESs, and SESs. This newer technology, used in
the Inmarsat-C, Inmarsat-M and Inmarsat-B systems, has generally resulted in SES models
which are smaller in size, lower in weight, and in power consumption than Inmarsat-A models,
which are based on analog technology. Also, because of the more efficient use made by new
technology in utilizing the satellite resources, the CESs can offer their communications

services at lower user charges.

1.4 The Inmarsat-C system
The Inmarsat-C system was introduced in 1991 to complement the Inmarsat-A system, by
providing low-cost global communications on a small terminal, suitable for fitting on all
vessels, large and small. Its small size makes it especially suitable for smaller vessels, such
as yachts, fishing vessels or supply craft. Figure 1-6 shows a typical installation.

The Inmarsat-C system does not provide voice communications, but does provide a means of
sending text messages or data to and from an SES, using store-and-forward messaging. This
technique requires the user (at either end) to prepare the message/data on their end terminal,
then transmit it via the Inmarsat-C satellite system to the receiving end. There, after a delay
of a few minutes, the message/data may be printed, viewed and/or stored.


Chapter 1

The Inmarsat Satellite Communications Systems

Some ofthe Inmarsat-C communications services are listed next. More information is provided
in Chapter 6.
•
The ability to send or receive messages between an Inmarsat-C SES and a shore-based
telex terminal, personal computer or electronic mail (E-mail) service. Anlnmarsat-C
SES can also send text messages to a shore-based fax terminal. Specialized fax bureau
services are available to convey text messages from shore-based fax machines to
Inmarsat-C SESs.
•
The Enhanced Group Call (EGC) services, which enable authorized shore-based
Information Providers to send information to selected groups of SESs - these may be

within a defined geographical area, or belong to a defined group such as a shipping
company. Two EGC services are available:
SafetyNETSM, which is used to broadcast Maritime Safety Information (MSI) to
ships.
FleetNETSM, which is used typically by companies to send commercial information
confidentially to ships belonging to their fleet.
The distress alerting and messaging capability of an Inmarsat-C SES, which may be
used to send a distress alert or message with top priority to a Rescue Co-ordination
Centre (RCC).

<)

<)

•

1.4.1

The Inmarsat-C system is part of the GMDSS

The global communications capability of the Inmarsat-C system, combined with its MSI
broadcasting and distress alerting capabilities, has resulted in the Inmarsat-C system being
accepted by the International Maritime Organization (IMO) as meeting the requirements of
the Global Maritime Distress & Safety System (GMDSS). The GMDSS requirements are
mandatory for passenger ships and merchant ships greater than 300 gross tonnes that make
international voyages. Fitting an Inmarsat-C SES is a cost-effective means for these ships to
meet GMDSS requirements, and for this reason, many ships are now being fitted with
Inmarsat-C SESs.
(Similarly, the Inmarsat-A and Inmarsat-B systems have also been accepted by the IMO into
the GMDSS. The Inmarsat-M system, however, is not at present accepted for use in the

GMDSS. Chapter 2 gives more information on the GMDSS.)

1.5 The Inmarsat-M system
The Inmarsat-M system was introduced in December 1992, to complement the existing
services, by providing global telephone communications on an SES which is inexpensive and
compact in size. As shown in Figure 1-4, an Inmarsat-M SES is smaller and lighter than an
Inmarsat-A SES, making Inmarsat-M suitable for smaller vessels such as yachts and fishing
vessels, as well as larger vessels such as cruise liners, and trading vessels. Figure 1-7 shows
a typical Inmarsat-M installation.
The services possible on an Inmarsat-M SES include two-way global telephone, fax and
computer data communications.
Inmarsat-M SESs can be purchased as either single-channel or multi-channel models (but note
that a multi-channel SES generally requires greater transmission power than a single-channel
SES, so the antenna and power supply for a multi-channel SES model would be larger and
of higher gain than for a single-channel SES).


The Inmarsat Satellite CommunicationsSystems

Chapter 1

1.6 The Inmarsat-B system
Inmarsat-B is intended as the successor to Inmarsat-A, providing its services at generally
lower charges than Inmarsat-A, although the two systems will co-exist for many years.
The Inmarsat-B system, introduced in 1994, uses digital technology to provide high quality
telephone, fax, telex and data communications, with the antenna size and weight approximately
the same as that of Inmarsat-A (Figure 1-4).
Single-cilbe capable of high-speed data communications (at up to 64 kilobits/sec), making it especially
suitable for data-intensive users such as oil companies and seismological companies, which

need to exchange large amounts of data on a regular basis.

1.7 Using Inmarsat in the shore-to-ship direction
This Handbook is aimed primarily at those using an Inmarsat system on board a ship. It is
useful, however, to know how the system is used by shore subscribers in the shore-to-ship
direction.
Although calling procedures for different Inmarsat systems may differ between countries, the
shore subscriber should generally experience no difference when making a phone, fax or data
call to a ship equipped with an Inmarsat-A, -B or -M SES. The same should apply for the
shore subscriber sending telex messages to a ship equipped with an Inmarsat-A or -B SES.
Different procedures apply, however, for the shore subscriber sending a message to an
Inmarsat-C SES - because of the "store-and-forward" techniques it uses, the message is first
stored at the CES, and then forwarded to the ship. Please see Chapter 8 for more information.



Chapter 2

Inmarsat Distress & Safety Services

2.1 Introduction
After many years of international consultation, the International Maritime Organization (IMO),
and its Member Governments developed the new Global Maritime Distress and Safety System
(GMDSS) with the co-ordination and cooperation of the International Telecommunications
Union (ITU), World Meteorological Organization (WMO), International Hydrographic
Organization (IHO), International Maritime Satellite Organization (Inmarsat), and COSP ASSARSAT. The GMDSS was incorporated into the SOLAS (Safety of Life at Sea) Convention
by amendments in 1988. Ships subject to the SOLAS Convention began implementation of
the GMDSS in 1992, and will complete implementation by 1 February 1999.
All ships will utilize the same safety system, but some will carry equipment on a mandatory
basis. Although the carriage of equipment for GMDSS operations is mandatory for SOLAS

Convention ships (cargo ships of 300 tons gross tonnage and larger, and passenger ships
making international voyages), all other ships will fit equipment to utilize the GMDSS on a
voluntary basis. Most ships (whether SOLAS or not) will find it desirable and convenient to
install Inmarsat type-approved equipment which will provide advantages for commercial
communications, and the added benefit of acceptance for GMDSS operation.


Inmarsat Distress & Safety Services

2.2

The role of Inmarsat in the GMDSS (see Footnote

2.2.1

Ship-to-Shore distress alerting

Chapter 2

1)

The Inmarsat system provides priority alerting for use in distress emergency situations.
Distress priority alerting applies not only with respect to satellite channels, but also to the
automatic routing of the call to the appropriate RCC (Rescue Co-ordination Centre). Each CES
in the system provides reliable communication with an RCC; these national RCCs are known
as 'associated RCCs'.
The means of CES-RCC interconnection may vary from country to country, and may include
the use of dedicated lines or public switched networks. Thus, any distress alerting message
received at the CES is automatically processed and passed to the associated RCC. Some CESs,
due to national considerations, may take either of the following actions:

•
Pass distress priority messages to special operators, who are responsible for the
subsequent routing of the call to the appropriate RCC.
•
In the Inmarsat-A and Inmarsat-B systems, these CESs may provide an option which
allows the shipboard operator to contact any RCC when a satellite channel has been
assigned on the distress priority basis.
You are advise to keep a copy of the appropriate pink pages (located at the front of each
chapter for a specific Inmarsat system) in a prominent position near your Ship Earth Station
(SES) in order to provide rapid assistance to anyone needing to send a distress alert. Make
sure that anyone who may ever need to make a distress call is familiar with its contents.

2.2.1.1 Inmarsat-A Distress Alerting
Each Inmarsat-A SES is capable of initiating a "request" message with distress priority
indication, which is automatically recognized at the CES, and a satellite channel is instantly
assigned. If all satellite channels happen to be busy, one of them will be pre-empted and
allocated to the SES which initiated the distress priority call. The processing of such calls is
completely automatic and does not involve any human intervention. The CES personnel,
however, are notified of the reception and passing through of a distress priority message by
audio-visual alarms.
To ensure the correct treatment of distress priority requests, the NCS in each Ocean Region
automatically monitors the processing of such calls by all other CESs in that region. In the
event that any anomalies in processing are detected, the NCS will take appropriate action to
establish the end-to-end connection. In addition, the monitoring NCS also checks the CES
identity contained in the distress priority message and automatically accepts the call if an
identity of a non-operational CES has been detected (which may happen due to operator error
aboard the vessel in distress).
The initiation of a distress priority message in some SESs is made by using a "Distress
button" on the SES. In other SESs, however the distress button changes the priority of the call
to distress priority (Priority 3), but does not initiate the distress message. On this type of SES,

the operator must still initiate the "Request" from the SES.
Most SES manufacturers provide instructions for the initiation of distress priority calls. These
instructions should be mounted close to the SES operating position, and should be studied by
all users, before they need to use them.


Chapter 2

Inmarsat Distress & Safety Services

On generation of a "request", by whichever means used, the SES transmits a priority request
via the satellite to a CES. In most countries, the CES which receives the request, automatically
makes a direct and assured connection to a competent Rescue Co-ordination Centre (RCC),
so avoiding the need for an SES operator to enter the telex or telephone number of the RCC.
If, however, a distress call is placed through a CES without automatic connection to an RCC
and the SES operator does not know the number of the RCC or is delayed in entering the
number, an operator, alerted by the Ocean region NCS, will intervene and offer any assistance
required. Thus no distress priority call will not go unanswered.
Inmarsat has issued technical guidelines to manufacturers for a Distress Message Generator
(DMG), which consists of SES software to transmit, after the connection has been established,
the distress message in a standardized format that provides information on the vessel's
identification, its position and the particular emergency.
2.2.1.2 Inmarsat-B Distress Alerting
Inmarsat-B SESs are capable of initiating telephony and telegraphy distress calls. For both
type of services, the call set-up and clearing procedures are identical. For ship-originated
distress calls, the SES maintains the ill of a particular CES in its memory, previously selected
by the SES Operator and modified automatically as necessary concerning current Ocean
Region and CES status as contained in the SES Network Status Record (derived from the NCS
Bulletin Board).
If during a ship-originated distress call (either telephony or telegraphy), the NCS determines

that the SES distress "access request" message contains an invalid CES ill, or that the
addressed CES has not sent a channel assignment message to the SES (after the expiry of a
timer for telephony) the NCS will replace the called CES ID field in the received distress
"access request" message with the ill of the back-up CES (and the return SES ill with the
forward SES ill) and then transmit a "distress access request relay" message to the back- up
CES. Upon receipt of this message, the back-up CES proceeds to set up the call as for any
ship-originated telephony or telegraphy distress call.
A mandatory Distress Message Generator (DMG) facility is provided in Inmarsat-B SESs with
telex capability (Class I SES). A pre-programmed telex distress message (containing SES ill,
position, course, speed, times of position up-date and activation) is maintained in the SES
memory. Once a duplex telex call is established on priority 3 (distress) basis (by pressing the
distress button), and the SES receives the GA+, then the operator can start to type the distress
message or use the stored message facility known as the Distress Message Generator (refer
to the SES manufacturer instructions).
Where the DMG facility is provided, the format of the DMG message complies with the
requirements of the International Maritime Organization (IMO).
The selection of distress priority, for telephony and telegraphy services is obtained by
pressing (and holding for six seconds) a "distress button".
2.2.1.3 Inmarsat-C Distress Alerting
Inmarsat-C SESs make use of the Signalling Channel for distress alerting. Using the distress
button, a short pre-formatted alert is transmitted directly to a CES, or to an NCS as a back-up.
Distress priority ensures special processing at the CES for expeditious transmission to the
associated RCC.
The distress alerting format in an Inmarsat-C SES may be updated manually from the terminal


Inmarsat Distress & Safety Services

Chapter2

keyboard. Automatic position updating, however, may be provided by an integrated electronic
navigation receiver, or by direct input from the ship's electronic navigation system.
2.2.1.4 Distress Communications
The procedures described above are the primary means of ship-to-shore distress alerting in the
Inmarsat systems. It should be noted, however, that Inmarsat SES-equipped ships can also
contact any RCC of their choice by following the calling procedure for routine calls. In this
case, the complete international telephone/telex number has to be selected.
A major benefit of Inmarsat distress priority systems is to make unnecessary the need for
dedicated frequencies to be allocated for distress and safety communications. Distress
messages transmitted through Inmarsat systems are sent through the general communication
channels on a priority basis to ensure rapid receipt.
2.2.2
Shore-to-ship distress alerting
Shore-to-ship distress alert relays will be transmitted via the Inmarsat-C SafetyNET service;
however, Shore-to-ship alerting to groups of ships with Inmarsat-A or Inmarsat-B SESs,
but without Inmarsat-C SafetyNET capabilities, can be performed in the following
modes:
All ships call - Calls to all ships in the Ocean Region concerned. It should be noted,
however, that due to the large coverage zones of geostationary satellites, such alerting is
not very efficient, although it may be justified under exceptional circumstances;
Variable geographical area calls - Inmarsat-B SESs can accept calls to rectangular or
circular areas, provided a navigational position is entered into the terminal.
Group calls to selected ships - This service is provided by a number of CESs in the
operator-assisted mode, and allows alerting of a predetermined group of vessels. This
service could be very useful for alerting, for example search-and-rescue (SAR) units.
As long as they are not engaged in traffic, SESs accept all incoming messages without any
differentiation of priority.
2.2.3
Shore-to-ship alerting through the Inmarsat SafetyNET service
The Enhanced Group Call (EGC) receiver can be an integral part of an SES, or a completely

separate unit, and it ensures a very high probability of receiving shore-to-ship distress alert
messages. When a distress priority message is received, an audible alarm sounds, and it can
only be reset manually.
Accessing the Inmarsat SafetyNET service by RCCs requires arrangements similar to those
needed for shore-to-ship distress alerting to an SES. Those RCCs unable to obtain a reliable
terrestrial connection to a coast earth station can install an Inmarsat SES at the RCC. The
RCC would then transmit the distress alert relay via the SES to an Inmarsat CES, where it
would be relayed by means of a broadcast through the SafetyNET service. See Paragraph 6.4
in Chapter 6 for more information on the SafetyNET service.
2.2.4
Search-and-rescue (SAR) co-ordinating communications
For the co-ordination and control of SAR operations, RCCs require communications with the
ship in distress, as well as with units participating in the operation. The methods and modes
of communication used will be governed by the capabilities available on-board the ship in


Chapter 2

Inmarsat Distress & Safety Services

distress, as well as those on-board assisting units. Where those ships are equipped with SESs,
the advantages of the Inmarsat system for rapid, reliable communications, including the receipt
of Maritime Safety Information (MSI), can be exploited.
A reliable interlink of RCCs is important for the GMDSS, in which a distress message may
be received by an RCC thousands of miles away from where the assistance is needed, and it
may not be the RCC best suited to provide the necessary assistance. In such cases, prompt
relay of the distress message to the appropriate RCC is essential, and any communications
means, whether landlines, terrestrial radio networks or satellite links, must be used.
To increase the speed and reliability of inter-RCC communications, some RCCs have installed
SESs providing them with the capability of communicating via the Inmarsat system. These

facilities are useful for long-distance interconnection of SAR organizations, especially when
dedicated lines or public switched networks are unavailable or unreliable, as well as for
communications with ships.

2.2.5

On-scene SAR communications

On-scene communications are those between SAR vessels and the OSC (On-scene
Commander), or the CSS (Co-ordinator Surface Search), and are normally short-range
communications made on the VHF or MF distress and safety frequencies in the GMDSS.
However, Inmarsat SES-fitted ships can, if necessary, use satellite communications to
supplement their VHF and MF facilities.

2.2.6

Promulgation of Maritime Safety Information (MSI) via Inmarsat

In the Inmarsat system, promulgation of MSI for the International SafetyNET Service is
performed by means of the Inmarsat-C EGC capability. If uninterrupted receipt of MSI is
required, or the Inmarsat-C SES is utilized for above average amounts of communications,
then it is essential for the ship to have a dedicated EGC reception capability for MSI
broadcasts. An EGC receiver is usually an integral part of an Inmarsat-C SES, but may also
be installed as a separate unit. Refer to chapter 6 for more information

2.3 General overview of the Inmarsat-E system
The Inmarsat-E system makes use of the existing Inmarsat infrastructure to provide a costeffective means of distress alerting. An Inmarsat-E EPIRB (Emergency Position Indicating
Radio Beacon) is defined as an L-Band geostationary satellite EPIRB approved by Inmarsat
for the GMDSS ship-to-shore distress alerting function over the Inmarsat space segment.
Frequency shift keyed transmissions from the Inmarsat-E EPIRB, operating at an information

rate of 32 bits per second, are received by an Inmarsat spacecraft in geostationary orbit,
where they are amplified, changed in frequency, and re-transmitted to earth.
The signal is received at all Inmarsat-E CESs, within satellite coverage, amplified, converted
to an intermediate frequency (IF), and fed to the Digital Receiver Processor (DRP). The IF
signal is converted to baseband in the receiving processor and digitized. Consecutive frames
of the transmission are stored and superimposed on one another to enhance the signal-to-noise
ratio in the memory.
The system design allows for very low signal power and effects of motions and Doppler shift.
Once a satisfactory signal-to-noise ratio has been achieved, and any errors corrected, the
message is decoded and routed to the RCC over the international packet switching network
(X.25). Alternatively, the conventional telex network is used for this purpose. Delivery of a


Inmarsat Distress & Safety Services

Chapter 2

distress alert to an RCC is very fast, typically one minute.

2.3.1

Inmarsat-E EPIRBs

Each EPIRB model is subject to type approval by Inmarsat. The purpose of Inmarsat's type
approval procedures is to ensure that EPIRBs will perform satisfactorily within the system,
and not endanger the integrity of system operations. The specifications include that:
• The electrical portions are waterproof at a depth of 10m for at least five minutes.
• No damage is caused when dropped into the water from a height of 20 meters.
• A buoyant captive lanyard of at least 20 m length suitable for use as a tether is
provided. The installation should not cause entanglement in the ship's structure.

• The float-free release and activation mechanism releases the EPIRB before it reaches a
depth of 4 meters.
• A label indicating clearly the operating instructions for manual release is attached at a
prominent place on the unit.

2.3.2

Technical description of an Inmarsat-E EPIRB

Distress alerting transmissions are made alternately in the frequency ranges from 1644.3 to
1644.5 Mhz, and 1646.6 to 1645.8 Mhz, in order to be received from both the first and
following generations of Inmarsat spacecraft. Transmissions consist of consecutive bursts of
the 160 bit message frame for each 10 minute activation period. EPIRBs are installed in buoys
which are designed to "float free" from a sinking vessel, and will normally be activated either
automatically by immersion in sea-water, manually from the local control, or remotely from
the ship's bridge. Mechanical construction of the manual input pad or data interface allow for
remote operation of the buoy, and for entry of the nature of the distress in the message.
The EPIRB transmits a distress message in the format shown in Table 2-1. In case of failure
of the ship's power or data interface, the last update stored within the EPIRB is included in
the Distress Message Generator.

2.3.3

EPIRB configurations

In general, an Inmarsat-E EPIRB consists of a buoy, which carries antennas and necessary
electronic equipment, power supplies, control panel, and an interface to ship's power supply,
remote activator and navigational aids. The buoy is held in place until it is released manually
or by the float-free mechanism. The interface may be done by means of conventional plugs
and sockets, or by cordless connection.

Position may be derived from the ship's electronic navigation system or a GPS receiver built
into the EPIRB, enabling location to be determined to a high degree of accuracy. This
precision, coupled with the rapid delivery of the message, greatly improves the efficiency with
which SAR (Search and Rescue) forces can be deployed.
Most EPIRBs have integral navigation receive capability, enabling the position to be updated
automatically. In this case, data may be fed directly into the Distress Message Generator.
Alternatively, the data interface bus may include a direct feed from the ship's navigation
equipment and the information entered by means of a serial data link.


Chapter 2

Inmarsat Distress & Safety Services

Inmarsat-E EPIRB installations provide the means to test the equipment without access to the
space segment, to indicate current emission of a distress alert and any fault in the equipment.
Along with the L-Band transmitter, Inmarsat-E EPIRBs are also equipped with a light of 0.75
candela, flashing with a low duty ratio, which is automatically activated by the onset of
darkness. Some EPIRBs will also include a 9GHz Search and Rescue Radar Transponder
(SART) for locating purposes.

2.3.4

Inmarsat-E Distress Alerting Networks

Eight Inmarsat-E Coast Earth Stations (CESs) and four Inmarsat-E Rescue Co-ordination
Centres (RCCs) form the Inmarsat-E distress alerting network. The satellite network consists
of a Digital Receiver Processor at the CES, connected to the associated RCC. They duplicate
operations in each Ocean Region to ensure a 100 per cent availability of the EPIRB to the
RCC link. Approximately 85 per cent of the Inmarsat-E global coverage is backed-up by at

least two operating satellite networks.

2.3.5

EPIRB registration

The purpose of registration is to facilitate effective and rapid assistance to people in distress.
This depends on availability of essential information related to registered EPIRBs. The
information also facilitates RCC actions in identifying the EPIRB, validating the distress
situation, and taking control over illegal use of the Inmarsat-E distress alerting system.