Ian Waugh - A Mariner\'s Guide to Marine Communications

allocating a share of the available bandwidth for each call, dynamically
(i.e. as required). An example of a simple private network for a single
ship is shown in figure 8.10.

I ,/ hi~h bandwidth

/ ~ dedical/' ed wmmunicatiolls ch.lllld ~

STATIO:--< LO\ND

ABOVE DECK

BELOW DECK

,

COMI'ANY OFFICE

~ Cl·' 6.

Locnetnl wo rk arc.

(I .AN

.~

PBX :1 Te lephand o nes

fax

machin es (on

demand)

I ;;:~ ::_.l I

LocaJ li area

network

iL ... N

:J

PBX

machine :; Fa:"

Figure 8. 70

Multi-channel private satellite network

The multi-channel installation

SHIP

I NSTALL<\T1 ON

Telephone!; ~

and fa.,

mac.hin('s (on

demand)

1 Antenna: typically 2·7 metres in diameter. The larger antenna is

required to handle more than one call at a time. Like other satellite

communications antennas, it is covered in a protective radome. A

modulator-demodulator (modem) is provided at each end to combine/

extract your voice/fax/data with/from the carrier frequency.

2 Multiplexer: allows multiple calls to be connected into a single

antenna, allocating different carrier frequencies within the allowed

bandwidth.

3 Private Branch Exchange (PBX): distribues/connects telephone/

fax calls within the ship/office, and to the satellite communications

system (via the multiplexer/modem). Direct access may be available

to/from the Public Switched Telephone Network (PSTN - number 7

on Fig 8.10) at the office exchange - or such access may be restricted.

MARINE COMMUNICATIONS 175