.: General Features :.
Vox Maris simulates a Fleet 77 station providing the main services of the system directly related to the GMDSS:
- Speech: Vox Maris presents a handset which is primary used to make telephone calls. Furthermore it can be used to configure the device and to display error and status messages.
- Distress calling: Vox Maris presents a cradle with a Distress Button, a Distress Stop button and three LEDs. The distress button, which is protected by plastic glass, is used to initiate a distress call. The Distress Stop button can be used to abort a distress call. The three LEDs indicate power, distress test and priority calls.
The operation is very simple, allowing the user to learn about distress, urgency, security and routine communications. The operation and the graphical display of the equipment are simulated emulating real equipment available in the market, allowing operation in the same way that it would on the real equipment (touch-screen is also possible).
The following is a list of the most important functions of the Fleet 77 simulated in Vox Maris:
- Handset for telephony communications
- Transmission / reception of telephony communications
- Communications of Safety and Emergency
- Distress communications
- Automatic Distress Button
- Agenda stations (IMN)
- Communications Log
- Distress button TEST
In order to provide global communications for ships, land mobile equipment and aircraft, using satellites to overcome the problems that exist with conventional radio communications, the Inmarsat system operates a network that includes a space segment, a ground segment and ground station mobile.
The space segment consists of four Inmarsat satellites, one for each ocean region. These satellites rotate in orbit above the Equator line at the same speed of the Earth. Thus, geostationary satellites remain fixed on one position of the Earth making the service available for any station located on the earth between 70°N and 70°S latitudes.
Each satellite orbits at an altitude of 35700 km. The satellites work as repeater stations between Land Earth Stations (LES) and Mobile Earth Stations (MES), allowing communications for several services such as Inmarsat B, C, M, FleetNET and Fleet77.
The satellites enable connection to the worldwide networks. The Inmarsat system consists of an Operations Control Centre (OCC), Satellite Control Centre (SCC), 4 Network Control Stations (NCS) (one for each Ocean Region), Fixed Land Earth Stations (LES) and Mobile Earth Stations (MES):
- The OCC, located at Inmarsat headquarters in London, coordinates a wide range of activities within the Inmarsat system, including commissioning of mobile earth stations (MES).
- The NCSs constantly keep track of which terminals are logged on to the system and assign a free channel whenever a call is made. The transmission and reception of signals are coordinated by the NCS. Thus, each NCS monitors the flow of communications through its satellite to ensure that communications are properly established and LES stations are properly working.
- The gateway between the public network and the satellites is operated by Land Earth Stations (LES). The LESs are operated by different operators around the world.
The Inmarsat Fleet service supports the following features:
High speed services
- 128 kbit/s data service
- 64 kbit/s data service
- 56 kbit/s data service
- Speech: High quality voice connections (It is the service simulated by Vox Maris)
- 3.1 kHz audio: For analogue signals transmission like fax or modems
- MPDS: It is a packet data service where the tariff depends on the amount of data sent and received.
Low speed services
- Mini-M voice: This service is only for voice transmission. The voice transmitted over the satellite is subject to a compression process that reduces the bandwidth to 4.8 kbit/s and consequently reduces the cost.
- 9.6 kbit fax: It allows sending and receiving fax messages using a standard office fax machine in a more cost effective solution than the 3.1 KHz audio service.
The low speed services have a lower tariff than the high speed services because the high speed services are high quality audio or high speed data services that require more bandwidth.
In order to use the different Inmarsat Fleet services, it is necessary to have at least one Inmarsat Mobile Number (IMN) for each of the above mentioned services. In case all 8 services are commissioned on a terminal, it will have 8 IMN different numbers.
A Fleet 77 station provides basically an Antenna (ADU - Above Deck Unit), an Electronic Units (BDU - Below Deck Unit) and a Handset and Distress Cradle:
The Above Deck Unit consists of Servo stabilized antenna dish with RF-Transceiver and a Mast or Deck mounted radome.
The Below Deck Unit constitutes the major electronic part and provides the hardware interfaces to connect several devices: 2 Handsets and connectors for 3 Analogue RJ11, ISDN, USB, Ethernet, Serial connector, NMEA 0183, Discrete I/O connections.
Handset and Distress Cradle
The handset is primary used to make telephone calls. Furthermore it can be used to configure the BDU and to display error and status messages.
The cradle has a distress button, a Distress Stop button and three LEDs. The distress button, which is protected by plastic glass, is used to initiate a distress call. The Distress Stop button can be used to abort a distress call. The three LEDs indicate power, distress test and priority calls.