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the modified Baudot spacc ("100100") being used where no
character exists.
2.3.9 Bits 84 and 85 shall indicate any homing transmitter
that may be integrated in the EL.
Table 5-1. Modified Baudot Code
Code Code
Letter MSB LSB Figure MSB LSB
MSB = most significant bit
LSB = least significant bit
* = hyphen
** = space
4/11/99
No. 74
Attachment A to Part I
GUIDANCE MATERIAL FOR AERONAUTICAL
MOBILE-SATELLITE SERVICE
1. INTRODUCTION
Packet data performance: Annex 10, Volume 111, Part I,
Note.-- The aemnautical mobile-satellite service (AMSS) Chapter 4, 4.7.2
Standards and Recommended Practices (SARPs) referred to
are contained in Annex 10, Volume III, Part I, Chapter 4.
1.1.6 CIRCUITM ODE VOICE
PERFORMANCE
1.1 Overview
1.1.1 The major elements of the aeronautical mobilesatellite
service (AMSS) are the space segment (the satellites
and their controlling earth stations); the ground earth stations
(GESs) that provide interfaces between the satellite and fixed
terrestrial voice and data networks; and the aircraft earth
stations (AESs) that comprise the avionics and antenna
systems on-board the aircraft.
Note.- Several operators of AMS(R)S may operate
independent but compatible satellite networks. The diferent
operators should co-operate in order for AESs to move
seamleflsly among the diferent networks.
1.1.2 The system architecture is capable of meeting a
range of communication requirements which may include
ATS, AOC, AAC and APC. The same system architecture is
used for various service levels, from the basic low data-rate
service to a multi-channel high data-rate service.
1.1.3 The level of capability of an AMSS system can be
chosen to suit the performance required by the application.
Note I.- The performance of a service will be set by the
lowest level of capability available in the chain of GES, space
segment and AES.
Note 2.- While a low level of capability service will have
lower capital costs, it may have higher satellite user charges
for the same data flow.
1.1.4 The capabiIities are summarized in Table A-1 * of
this guidance material.
1.1.5 The examples of performance given in this section
are to give a quick look at the over-all system performance. If
exact figures are required, the relevant paragraphs of
Annex 10, Volume III. Part I. Chapter 4 should be studied.
Assuming that the AES is logged on to a GES, the AMSS will
typically take the following times to set up a call:
from-aircraft:
-Use of abbreviated access request SU: 10 to 14
seconds (average)
-Use of general access request SU: less than 17
seconds (average)
to-aircraft: 9 to 11 seconds (average).
Note.- The call set-up time may be affected by the
pe#omnce of the associated terrestrial network.
1.2 Levels of capability
1.2.1 The various levels of capability for the aircraft earth
station (AES) and ground earth station (GES) defined in
Annex 10, Volume 111, Part I, Chapter 4, 4.1.3 allow various
capabilities to exist which have different performance
characteristics. A Level 1 capability is the minimum capability
required for aeronautical mobile-satellite (route) service
(AMS(R)S) providing basic packet data communications. A
Level 3 is required as a minimum when, in addition to packet
communications, circuit voice communications are required.
All levels of capability require that the ffiS be under positive
control either by receiving a P channel signal or through the C
channel sub-band. Only one of the channel rates indicated
below is required to operate at any given time.
1.2.2 The Level 1 capability provides for basic packet
data communications by requiring an AES to receive and
process a P channel signal operating at channel rates of 0.6 and
1.2 kbits/s. It also requires the capability for an AES to
transmit on an R channel or on a T channel at these channel
System capabilities: Annex 10, Volume ID, Part I,
Chapter 4, 4.1.3 * All tables are located at the end of this attachment.
ANNEX 10 - VOLUME I11
Annex 10 - Aeronautical Telecommunications Volume I22
rates. Both R and T channel capabilities are required. The
channel rate used will depend on the link quality determined
by the GES measurement of bit error rate (BER) or the
estimate of that BER. Major factors that determine the channeI
rate are the antenna gain of the satellite and AES, and the RF
power output of the satellite and AES. Level 1 requires one
transmit channel (for R or T channel) and one receive channel
(for P channel).
1.2.3 The Level 2 capability provides for channel rates of
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