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channels would violate the data tmnsfer delay requirements
specified in Annex 10, Volume 111, Part I, Chapter 4, 4.7.
10.5.1 The AMSS system, which forms part of the
ICAO communications, navigation, and surveillancelair traffic
management (CNSIATM) systems concept, provides cornmunication
services on a global basis. The AMSS system architecture
consists of a number of satellites and a limited number of
GESs. All Statesladministrations can have full access to the
AMSS, but most of them will not need to have their own
GES; rather they will connect to the network through service
providers.
Annex 10 - Aeronautical Telecommunications Volume III
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 reasons such as:
a) redundancy - reducing the impact of GES failure;
b) less dependency 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
specwum into small pieces;
b) degraded packet data performance as AESs are
subjected to more log-on/log-off cycles as they transit
between various flight information regions (FIRS)
which operate their own GESs;
c) increased workload for the flight crew (or cost and
complexity of the AES) as they transit between various
F'LRs which operate their own GESs.
10.5.4 Additional factors which affect the number of
GESs are the following:
a) available satellite power will limit the number of 600
bit/, P-channels, i.e. GESs, which can be supported
per satellite; and
b) the cost of installing and operating a GES will not be
economical for most administrations.
Given this, some States may be concerned about their dependency
on ocher States or service providers, for GES services.
This concern can be alIeviated by several considerations:
a) For packet services, the ATN will allow States without
GESs to choose between a number of different States
or service providers to obtain GES services.
b) In Stares where the ATN is less developed, fixed
satellite links between a GI3 and the air traffic control
centre could provide an alternative to terrestrial links.
This approach could be a source of both costcompetitiveness
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 second satellite link may not be adequate for voice
communications, at least not in a normal conversation
mode. However, its effect on verbal exchanges typical
of ATC applications has not been studied.
C) States should have adequate institutional arrangements
with service providers based on ICAO guidelines for
AMSS.
Atlachment A to Part I Anna 10 - A e r o ~ ~ t i cTaell ecommunications
TABLES FOR ATTACHMENT A
Table A-1. Typical implementation versus levels of capability
Packet data Circuit mode
Levels of service service Number of AES antenna
capability (kbitsts) (kbitsls) channels gain Comments
1 0.6 Not available 1 transmit 0 dB
1.2 1 receive
2 0.6 Not available 1 transmit 12 dB Higher sped for packet
4.8 1 receive data
10.5
3 0.6 Voice 1 transmit 12 dB Fkvides digitized voice,
4.8 21 .O 2 receive and packet data but not
10.5 simultaneously
4 0.6 Voice 2 or more 12 dB Simultaneous two-way
4.8 21.0 transmit packet and voice. Needs
10.5 2 or mote linear amplifier and power
receive control for each carrier.
NOTES:
I . Circuit mode data services may be supported by some implementation, but these are not defined in the AMSS SARPs.
2. The 4.8 kbitds channel applies only to the P channel.
Table A-2. Worst case data performance versus channel rate
Residual error rate:
from-aircraft direction: lo4 per SNSDU (maximum)
to-aircraft direction: per SNSDU (maximum)
Minimum Maximum connection
channel rate establishment delay
in use by AES (95th percentile)
(bitis) (seconds)
NOTES:
1 . In any particular AES, lower priority from aircraft traffic may be subject to additional delay, depending on the amount and
rate of from-aircraft traffic loading.
2. The values of the transfer delays arc based on packet sizes of 128 octets.
Transit delay (average) (seconds)
To-aircraft
Highest Lowest
priority priority
Data transfer delay (95th percentile)
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