Glossary

AA (accounting authority): The organization named on a commissioning application form to administer the billing and settlement of the communication charges incurred by an MES. AAIC (accounting authority identification code): An unique code assigned by the ITU to identify an accounting authority. AMVER (Automated Mutual-assistance Vessel Rescue system): A vessel position-reporting system operated by the United States Coast Guard for any merchant vessel of 1000grt or more on a voyage lasting longer than 24 hours, to and from anywhere in the world. Analogue: Any signal which represents a changing value over time. Answerback: An identifier given to an Inmarsat MES and used in message transmissions. The format must be four letters (A-Z; no numbers) finishing with an x.

 

AOR-E: Atlantic Ocean Region (East).

 

AOR-W: Atlantic Ocean Region (West).

 

Applicant: The person who completes and signs a maritime commissioning application form when applying to have an Inmarsat MES commissioned. The applicant must submit the form to the national routing organization for the country where the vessel is registered.

 

ARQ (automatic request repeat): The error correction process used in store-and-forward messaging by which a receiver checks for errors in received data packets and requests the sending end to re-transmit any packets which were received containing an error.

 

ASCII (American Standard Code for Information Interchange): A standard alphanumeric character set based on 7-bit codes.

 

AUSREP: A vessel position-reporting system similar to AMVER, but operated by the Australian Authorities.

BBER: Bulletin Board Error Rate.

 

Bit: The basic unit of digital communications; may be either 1 or 0.

 

Bit Error Rate (BER): used as a measure of the quality of reception by the MES of the Bulletin Board of a TDM Channel.

 

Bulletin Board (in a TDM channel): A data packet transmitted in each frame of a TDM channel which contains information about the status of the Inmarsat B/M, mini-M and C network configurations and the current frame number, used by the MES as a timing reference.

 

BPS (bits per second): A unit of measurement for speed of data transfer or throughput.

 

Bulletin Board Service (BBS): A notice board on which information can be exchanged or posted for others to download.

 

Byte: One byte comprises eight bits and may represent either one alphanumeric character or numeric information 

CAG: Customer Activation Group.

 

Case-approval: The official approval given by Inmarsat to an MES model which is typically still undergoing development by a manufacturer so as to permit the model to access an Inmarsat communications system. See also type-approval.

 

CCITT (Comité Consultatif International Télégraphique et Téléphonique): An advisory committee to the International Telecommunication Union (ITU). The CCITT publishes standards and recommendations to enable telecommunications systems and equipment world-wide to communicate with each other. Examples of CCITT standards are the X.25 and X.400 protocols used on PSDN land-lines.

 

Channel number: The number representing the frequency of an Inmarsat communications channel.

 

Character: One element of an alphanumeric character set. One character is equivalent to one byte or 8 bits.

 

Class 1 Inmarsat C MES: A Class 1 MES is capable of ship-to-shore and shore-to-ship message transfer and distress alerting, but is not capable of receiving EGC messages.

 

Class 2 Inmarsat C MES: A Class 2 MES is capable of two modes of operation (selected by the operator):

As Class 1, and also capable of receiving EGC messages when not engaged in Inmarsat C traffic. Ready for EGC message reception exclusively

(and not available in that mode for Inmarsat C message transfer).

 

Class 3 Inmarsat C MES: A Class 3 MES has two independent receivers, one for receiving two-way Inmarsat C messages, the other for receiving EGC messages.

 

Closed network: A private network, with access limited to registered users. The Inmarsat C system allows two types of closed networks: data reporting networks, identified by a Data

Reporting Network Identification (DNID) code, and EGC FleetNET networks, identified by an EGC Network Identification (ENID) code. 

 

Commissioning: The process by which an MES is registered for use via the Inmarsat network. 

 

Companded: A method of transmission, meaning `compressed/expanded', which is used to improve signal-to-noise ratio. At the sending end, a `compressor' electronic circuit amplifies low-level signals and reduces high levels to a mean level according to an algorithm. At the receiving end, an `expander' circuit uses similar methods to return the signal levels to their original values before passing them on to other circuits. See also uncompanded.

 

COSPAS-SARSAT: A satellite-based distress beacon locating system.

 

Coverage area: See footprint.

 

CSS: Co-ordinator Surface Search.

Data report (programmed unreserved, P): A short collection of data (up to 32 bytes in three packets) which is transmitted by an MES at random times in unreserved time slots of a signaling channel after receipt of a polling command from an operational centre.

 

Data report (reserved, R): A small amount of data (up to 32 bytes in three packets) which is transmitted by an MES in reserved times slots in a signaling channel, in response to an earlier polling command from an operational centre.

 

Data report (unreserved, U): A small amount of data (up to 32 bytes in three packets) which is transmitted in unreserved time slots of a signaling channel by an MES to an operational centre.

 

Data services: This is how a terminal may send and receive electronic messages such as e-mail.

 

DCE: Data circuit terminating equipment: a component part of an Inmarsat C MES. An MES contains a DCE receiver and a DCE transmitter which are used for communication between the MES and an Inmarsat C LES.

 

DECCA Navigator: A position-fixing system, based on chains of shore-based radio transmissions.

 

DHSD: Duplex high-speed data (see HSD).

 

Differential GPS: A global positioning system used with Inmarsat terminals and based on GPS satellites, with accuracy enhanced by the use of transmission of differential corrections from suitably located shore-based radio beacons.

 

Digital: A signal which represents values in the form of binary numbers.

 

Distress alerting: A facility available on all maritime MESs, enabling the MES to send distress priority messages through the Inmarsat system to a rescue co-ordination centre (RCC). This is not available on the Inmarsat-mini-M network.

 

Distress priority message: This is a message prepared and sent with distress priority using the Inmarsat system to a rescue co-ordination centre (RCC).

 

DMG: Distress Message Generator.

 

DNIC: Data Network Identification Code.

 

DNID: Data reporting Network Identification code. See data report (unreserved), data report (reserved) and data report (pre-assigned).

 

Downloading: The process by which an Inmarsat C MES receives information from a service provider. For data reporting purposes, an operational centre downloads a DNID code and Member Number to the MES. In the EGC FleetNETTM service, an information provider downloads an EGC Network Identification (ENID) code to an MES.

 

DTE (data terminal equipment): a component part of an Inmarsat C MES, used primarily for storage and interfacing external devices (such as a keyboard or monitor). For other Inmarsat systems, this can be a computer connected to the MES for use for data communications.

 

Duplex: The ability of a communications channel to transmit data simultaneously in both directions. Also known as Full Duplex

EGC: The EGC (Enhanced Group Call) services provided in the Inmarsat C system are EGC SafetyNET, EGC FleetNET and Inmarsat system messages.

 

EIRP: Effective Isotropically Radiated Power, a measure of transmitted power.

 

E-mail: Electronic mail: a global message-handling system whereby subscribers to commercial e-mail services can exchange electronic messages and data files between computers. E-mail services are provided by some service providers and private organizations. Access to e-mail services may be via PSTN, PSDN networks or the Internet.

 

ENID: EGC network identification (ENID) code.

 

EPIRB: Emergency position-indicating radio beacon.

 

ESAS: Electronic Service Activation System.

Fax: Abbreviation for `facsimile', a device used to transmit a copy of an original document. The Inmarsat-A, B/M and mini-M systems support two-way fax transmissions. The Inmarsat C system is able to send only text messages (no graphics) to a fax terminal in the ship-to-shore direction. It is only possible to send text messages (no graphics) in the shore-to-ship direction by using a third party fax bureau.

 

Fax bureau service: A service offered by some private organizations and service providers to send and receive fax messages.

 

FleetNET: A service provided by FleetNET information providers to distribute commercial information to MESs belonging to a FleetNET group, identified by an unique ENID code.

 

Footprint (of a satellite): The area on the Earth's surface (sea or land) covered by the satellite and where an antenna can obtain line-of-sight communications. In the Inmarsat systems, this area is also known as the ocean region or coverage area.

Gateway: An interface between communications systems such as the Inmarsat C system and the national and international telecommunications networks.

 

Glonass: A global positioning system similar to GPS but using satellites of the former Soviet Union.

 

GMDSS: The Global Maritime Distress and Safety System: the Inmarsat-A/B and C systems are the only Inmarsat networks included in the GMDSS by the IMO International Maritime Organization.

 

Gold Franc (GF): A nominal currency used by LESs and accounting authorities to calculate communication charges incurred by an MES. A fixed rate of exchange exists between the GF and the nominal currency the SDR: 1 SDR = 3.061 GF.

 

GPS (Global Positioning System): System which provides the geographic location of a vessel. This service uses American military satellites which have been made available for civilian use.

 

Ground segment: The network of LESs which provide a link between the space segment and the terrestrial telecommunication networks.

HSD: High-speed data. This service allows for data to be transferred at data rates of up to 64kbit/s.

IA5: International Alphabet 5 - a standard alpha- numeric character set, also known as ASCII, based on 7-bit codes. Supports both upper and lower case characters.

 

IHO: International Hydrographic Organization.

 

IMN (Inmarsat Mobile Number): The number assigned by the national routing organization to an Inmarsat MES as its identity number.

An Inmarsat-A maritime IMN has the format 1xxxxxx;

An Inmarsat-B maritime IMN has the format 3xxxxxxxxx;

An Inmarsat C maritime IMN has the format 4xxxxxxxxx;

An Inmarsat-M maritime IMN has the format 6xxxxxxxxx;

An Inmarsat-mini-M maritime IMN has the format 76xxxxxxxx.

 

IMO: International Maritime Organization.

 

Information provider: An organization which provides MSI messages for broadcasting to MESs via the EGC SafetyNETTM service, which can be received by vessels fitted with an EGC receiver.

 

Inmarsat: The operator of global mobile satellite communications, part of the Inmarsat Ventures Ltd group of companies.

 

Inmarsat A: The original Inmarsat system, which has been operating since 1982, based on analogue techniques and capable of global two-way telephony, facsimile, data and telex communications.

 

Inmarsat B: An Inmarsat system based on digital technology, and capable of high quality telephony, facsimile, data and telex services.

 

Inmarsat C: A digital system based on a low-cost MES with low power consumption. This system provides global two-way store-and-forward messaging, distress alerting, EGC SafetyNETTM and FleetNETTM, data reporting and polling.

 

Inmarsat E: A distress alerting system based on EPIRBs. I

 

nmarsat M: Introduced in 1993, based on digital technology and capable of two-way voice telephony, distress alerting, fax and data services at lower data rates.

 

Inmarsat mini-M: Introduced in 1995, based on digital technology and capable of two-way voice telephony, alerting, fax and data services. Operates only in the reduced coverage offered by the spot beams

 

Inter-station Signaling Links (ISLs): These signaling channels are used between an NCS and the LESs in its ocean region to pass system information around the system.

 

Internet: An international network of computers linked to enable information to be exchanged.

 

IOR: Indian Ocean Region.

 

ISDN, Integrated Service Digital Network: A high capacity digital line which lets users send voice and data at 64kbit/s over one telephone line from a common network interface.

 

ISP (Inmarsat Service provider): An entity which establishes a contract with one or more of the SPs to bill, promote and retail the services of the contracted SPs to end users. It can be an alternative to an AA.

 

ITA2 (International Telegraph Alphabet 2): A standard alphanumeric character set, generally used for sending messages on the international telex networks. The character set is based on 5-bit codes, also known as telex format, or 5-bit packed.

 

ITU: The International Telecommunication Union, which publishes a list of approved accounting authorities. See also CCITT.

Kbytes: 1024 bits or 128 characters.

LAN (Local Area Network): A network which allows computers and printers to communicate with each other, have access to and share expensive peripherals such as fax servers, modem servers and centralized databases.

 

Land earth station (LES): The name used in the Inmarsat network for a shore-based receiving and transmitting station which acts as an interface between MESs and the terrestrial communications networks. LESs are owned and operated by service providers.

 

LES TDM channel: A TDM channel used by an LES to transmit system information and data addressed to an MES.

 

Log in: The action performed on an Inmarsat C MES to inform the NCS in an ocean region that the MES is available for communications.

 

Log out: The action performed on an Inmarsat C MES to inform the NCS in an ocean region that the MES is not available for communication.

 

LORAN-C: A position-fixing system, based on chains of shore-based, low-frequency radio transmissions.

MEM: Macro-encoded message.

 

Member number: The number downloaded with a DNID to an MES, when the MES is registered to a data-reporting network.

 

MES (mobile earth station): The generic name used to describe an Inmarsat-approved terminal which is allowed to access the network, and applicable to both maritime and land mobile communications.

 

Message channel: A channel assigned by the NCS for an MES to send a message through an LES to its required destination.

 

METAREA: Meteorological area corresponding to the NAVAREAs defined by the IMO.

 

MMSI (Maritime Mobile System Identity): A nine-digit format assigned by the maritime authority to identify a vessel. The first three digits are the code of the country where the vessel is registered as defined by the ITU.

 

Modem: MODulator/DEModulator, a device used to transmit digital data, by converting (modulating) a digital signal into an analogue form and re-converting (demodulating) the analogue signal into digital form at the receiving end.

 

MSI (Maritime Safety Information): Information supplied by shore-based information providers and forwarded to an Inmarsat C LES for broadcasting over the Inmarsat C system to MESs fitted with an EGC receive capability.

 

Multi-channel MES: An MES which is capable of making more than one call at a time. Most MESs are only single channel.

NAVAREA: One of 16 areas of sea as defined by the IMO, into which the world's oceans are divided for the dissemination of navigational and meteorological warnings. See also METAREA.

 

NAVTEX: The low-frequency system developed by the IMO for the broadcast and automatic reception of coastal MSI by means of direct-printing telegraphy.

 

NCS: An Inmarsat network co-ordination station; a specially equipped LES appointed as the NCS for each Inmarsat system and ocean region, which monitors and co-ordinates the operation of all of the MESs and SPs within that ocean region.

 

NCS Common Signaling Channel: Also known as the NCS Common Channel. A TDM channel used by the NCS to transmit system information and message announcements to MESs.

 

Network: A group of communication channels which enable the sharing of information and resources between several users.

 

NOC: Network Operations Centre, located at Inmarsat's headquarters in London, which monitors and controls the operation of the Inmarsat network.

 

NUA: Network user address.

Ocean region: The coverage area of an Inmarsat satellite within which an MES may send and receive messages.

 

Omega: A position-fixing system based on chains of shore-based, very-low frequency radio transmissions.

 

Omni-directional antenna: An antenna which is capable of line-of-sight communication with a satellite without requiring any pointing. Generally used on an Inmarsat C MES.

 

Operational centre: A shore-based centre for controlling a data-reporting network. The operational centre initially downloads a DNID code and member number to an MES which joins the group. The centre subsequently sends polling commands to instruct selected MESs to return pre-assigned data reports or to perform a defined task such as SCADA. The centre also receives unreserved data reports from MESs belonging to the closed network.

 

Operator-assisted services: Communications services provided by some service providers, for example forwarding a text message from an MES as a voice message to a shore-based telephone.

 

Option 1 stand-alone EGC receiver: A type of stand-alone EGC receiver which can receive only EGC messages and cannot engage in non-EGC message transfer.

 

Option 2 stand-alone EGC receiver: This type of stand-alone EGC receiver may be added to the antenna of an Inmarsat-A or B MES so that the vessel may meet its GMDSS requirements.

Packet: An `envelope' or block of data sent over a network; each packet contains addressing information as well as the data being sent.

 

Polling: The facility whereby an operational centre sends an instruction (a polling command) to selected MESs to perform a defined task, such as returning a pre-assigned data report or performing a SCADA operation.

 

POR: Pacific Ocean Region.

 

Presentation code: A code included in a transmission (ship-to-shore or shore-to-ship), indicating to the recipient the presentation or formatting of the data contained in the message.

 

Protocol: A defined set of communications standards which lay down the parameters to which all users must abide. Protocols in general use are X.25 and X.400.

 

PSA: Point of Service Activation.

 

PSDN: Packet Switched Data Network.

 

PSTN: Public Switched Telephone Network.

 

PVT: Performance Verification Test; used to test the performance of Inmarsat C.

RCC: Rescue co-ordination centre.

SafetyNETTM: This service is provided by SafetyNETTM information providers to distribute MSI to MESs fitted with an EGC receive capability.

 

SAR: Search-and-rescue.

 

SART: Search and Rescue Radar Transponder.

 

SCADA: Supervisory Control and Data Acquisition.

 

SCC: Satellite control centre.

 

SDR (Special Drawing Right): A nominal currency used by service providers and accounting authorities to calculate communication charges incurred by an MES. A fixed rate of exchange exists between the SDR and the nominal currency of the GF: 1 SDR = 3.061 GF.

 

Service provider (SP): A company or organization which operates an LES.

 

Signaling channel (MES - LES): A random access TDMA channel, used by an MES to transmit signaling information and data to an LES.

 

Signaling channels (MES - NCS): A random access TDMA channel, used by an MES to transmit signaling information and data to an NCS.

 

SIM (Subscriber Identity Module) card: Used with Inmarsat mini-M, SIM cards are easily installed and removed, allowing one terminal to be used by multiple users without having complex billing arrangements.

 

Simplex: The ability of a communication channel to carry communication traffic in one direction only.

 

SOLAS: Safety of Life at Sea.

 

Space segment: Consists of the communications satellites operated by Inmarsat.

 

Special access code: A destination address code used in a ship-to-shore or shore-to-ship message to access a special service provided by a service provider. The two-digit codes are examples of special access codes.

 

Spot beam: A concentrated area offering coverage within the global footprint for particular regions in the world.

 

Store-and-forward messaging: The protocol used by the Inmarsat C system to transfer text or data messages in data packets to receiving equipment.

 

System message: A message originated by Inmarsat containing information relevant to the Inmarsat system, broadcast on the NCS Common Channel and received by all MESs.

TCP / IP (Transmission control protocol / Internet protocol): The set of protocols used to communicate via the Internet and between multiple networks.

 

TDM (Time division multiplex): The process by which multiple signals can share the same communication channel, each using a different time slot.

 

TDM channel: The Inmarsat system uses different TDM channels, each transmitted on an unique frequency. The TDM channels are used for system control and message transfer to MESs. See LES TDM Channel and NCS Common Channel.

 

TDMA (Time Division Multiple Access): The process by which MESs communicate with an LES or NCS.

 

TNID: Terrestrial Network Identity.

 

Terrestrial telecommunication networks: The national and international telephone, telex and data networks with which the service providers interface to route calls to and from MESs via the space segment.

 

Time slot: Basic unit into which one time frame of a TDM channel is divided.

 

Type-approval: The official approval given by Inmarsat to an MES model produced by an independent manufacturer when the MES meets the technical standards defined by Inmarsat. Only models which have been granted type-approval (or case-approval) are permitted to operate via the Inmarsat network.

Uncompanded: A method of transmission which does not use companding techniques and is used for data and fax transmission on the Inmarsat-A network. See companded.

 

UTC (Universal Co-ordinated Time): A term which, for practical purposes, has the same meaning as Greenwich Mean Time (GMT).

Value-added service (VAS) provider: A private organization which provides services such as weather forecasting to vessels using Inmarsat and other networks.

 

Video conferencing: Video and audio communication between two or more people via a videocodec (coder/decoder) at either end and linked by digital circuits.

WAN (Wide Area Network): A network which connects users over large distances, often crossing geographical boundaries.

 

WMO: World Meteorological Organization.

X.25: The communications protocol used on the national and international PSDN networks to exchange digital data between devices attached to the network.

 

X.400: A message-handling protocol used to exchange electronic mail (e-mail) messages around the world. Able to use the X.25 (PSDN) networks.

Two-digit codes: Special examples of Special Access Codes. See Tables D-1 and D-4, Appendix D.

 

5-bit packed (also known as telex format or ITA2): A format based on 5-bit codes used for sending alphanumeric characters to and from telex terminals.

 

7-bit ASCII: A format based on 7-bit codes used for sending the alphanumeric characters of the ASCII character set.

 

8-bit data: A format based on 8-bit codes used for encoding information such as text, national character sets and numerical information.