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broadcasts a partial sequence on all its operational P channels.
Each satellite service area has its own system table and spot
beam map broadcast information.
10.4.5.1.4 The system table complete and partial
sequence' broadcast rates may be reduced due to high P
channel loading. This may delay the initiation of the log-on
procedure at the AES. It is recommended that the GES
management monitor such broadcast rates and pvide further
P channel capacity to maintain these rates at acceptable levels.
10.4.5.1.5 The system table consists of :
a) system table broadcast index SU (figure A2-30,
Chapter 4, Annex 10, Volume III);
b) system table broadcast satellitelbeam ID channel advice
SU (Figu~A 2-32, Chapter 4, Annex 10, Volume III);
C) system table broadcast QES P/R channel advice SU
(Figure A2-31, Chapter 4, Amex 10, Volume m);
d) system table broadcast GES beam support advice SU
(Figures A2-34 and A2-61, Chapter 4, Annex 10,
Volume Ill); and
e) system table broadcast data channel EIRP SU (Figure
A2-62, Chapter 4, Annex 10, Volume Ill).
'The system table broadcast data channel EIRP SU is used by
the AES in accordance with 4.10.4.4.3.1.1 of Annex 10,
Volume III.
10.4.5.1.6 Where a satellite supp~rtssp ot beam service, a
GES transmits the spot beam map series consisting of SUs as
shown in F i i A-21 of this guidance material. This sequence
is independent to the system table hadcast series and
contains the definition of the spot beam coverage areas and the
GES services supported in the spot beams. The AES, upon
receiving the complete series, will then know what spot
beam(s) it is currently in and the services that are available to
it. The AES may use this information to determine which GES
to log on to. The message types for the spot beam map series
are:
A#achme~t A to Part I Annex 10 - Aem~utZcal Telecommunic&ns
18 spot beam map broadcast - complete sequence -
initial SU
19 spot beam map broadcast - complete sequence - SSU
26 spot beam map broadcast partial sequence - initial SU
27 spt beam map broadcast partial sequence - SSU
10.5 considerations for GES services
10.5.1 Tlw AMSS system, which forms part of the ICAO
communications, navigation, and surveillancdair tra&c
management (CNS/NM) systems concept, provides
communication services on a global basis. The AMSS system
architecture consists d a number of satellites and a limited
number of GESs. All Statesfadministrations can have full
access to the MASS, but most of them will not need to have
their own GES; rather they will connect to the network through
service providers.
10.5.2 Although a small number of GESs are sufficient
for AMSS in a given geographical area, some States or
administrations may feel it is necessary to install and operate
their own GES for reams such as:
a) redundancy - reducing the impact of GES failu~;
b) less &pendency on other States (who operate GESs) and
service providers; and
C) exerting authority and control in their airspace.
10.5.3 However, the proliferation of GESs can lead to
problems such as:
a) increased demand for spectrum because of the
inefficiencies introduced by dividing the available
spectrum into small pieces;
b) degraded packet data performance as AESs are
subjected to more log-oflog-off cycles as they transit
between various flight information regions (FEEls) which
operate their own GESs;
c) increased workload for the flight crew (or cost and
complexity of the AES) as they transit between various
FIRS which operate their own GESs.
10.5.4 Additional factors which affect the number of
G B s are the following:
a) available satellite power will limit the number of 600 bit/
s P-channels, i.e. GESs, which. can be supported per
satellite: and
b) the cost of installing ad operating a GES will not be
economical for most administrations.
Qiven this, some States may be concerned about their
dependency on other States or service providers, for GES
services. This concern can be alleviated by several
considerations:
a) For packet services, the PlTN will allow States without
GESs to choose between a number of different States or
service providers to obtain GES services.
b) In States where the MN is less developed, fixed satellite
links between a GES and the air tr&c control centre
could provide an alternative to terrestrial links. This
approach could be a source of both cost-competitiveness
and redundancy. If designed properly, the extra delay
introduced by a second satellite link will have a
negligible effect on the packet data performance. A
　
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