4 Telephones: - connected to the PBX can be allowed unrestricted
access (subject to lines being available - typically 8 calls can be made
at a time) or access may be limited and/or barred. This allows calls to
be charged, for example, to passenger's cabins or ship's offices - but
prevents calls being made from locations where there is no control
over who may use the telephone.
5 Facsimile (Fax) Machine: - in this arrangement, the fax machine is
usually connected to the PBX.
6 Local Area Network (LAN): - the onboard/ office computer network- allows exchange of e-mail and data between ship and office.
High-capacity versus on-demand. As mentioned earlier, individual
Inmarsat-B/M units can be multiplexed into the same type of large
antenna used for the high-capacity system. The management decision
between leased capacity against on-demand capacity will often be a
financial one - measuring cost of installation and call charges of one
system against another. Other factors, including reliability, durability
and usability will also play their part.Equipment tests and checks
This type of network/installation is unlikely to be fitted onto avessel that does not carry an Electro-Technical Officer (ETO) and/or an
Information Technology (IT) specialist. It is not likely to benefit from
any user tests and checks, or maintenance routines, other than those that
may be specified in the installation/ operations manual provided.
Other Mobile Satellite Systems
The development of combined cellular-radio and satellite
communications, in recent years, promised the best of both worlds: low
cost cellular calls when within range of a land cellular radio service;
switching to the higher-cost satellite service only when out of cellular
range. A number of systems have been proposed. Some failed to
materialise before becoming operational and others failed to generate
enough revenue to fund the continuation of the system.
Some systems promise global (worldwide) coverage and others
are regional (covering only part of the earth's surface). Some systems
offer combined cellular and satellite access from a Single handset that
can, in some models, be converted to a fixed unit onboard a ship for
connection to a maritime antenna (of similar size and weight to Inmarsat
Mini-M - but omnidirectional rather than a moving dish antenna).
176 THE NAUTICAL INSTITUTE