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Figure A2-35) containing the current time to the nearest
second, synchronized to the UTC standard has been defined in
the AMSS SARPs. Upon receipt of a universal time SU from
the GES, the AES may provide the received time information
to the appropriate applications on the aircraft. The method
selected by the AES to provide this time information to an
application is implementation dependent.
9.3.2.4 User commnds
9.3.2.4.1 The AMSS SARPs specify the AES responses
to a minimum set of commands intended to influence some of
the AES operations. Such commands may be initiated either
prior to (Annex 10, Volume 111, Part I, Chapter 4, 4.9.3.3.3.1)
or after (Annex 10, Volume 111, Part I, Chapter 4, 4.9.3.3.4.2)
the AES log-on. Neither the sources nor the formats of such
commands are specified in the AMSS SARPs. Such sources
may be internal or external to the AES and operating in
accordance with some stimulus criteria to satisfy a particular
user requirement, such as continuity of service. For example,
a stimulus criterion to invoke a beam-to-beam handover could
be based on the knowledge of the beam pattern of a given
satellite and the position and heading of the aircraft. The
formats of the handover commands are implementation
dependent.
9.3.2.4.2 Haradover commattds. The handover commands
specified in the AMSS SARPs are intended to enable the AES
user to alter the AES log-on conditions in various ways, as
deemed suitable by the user.
9.3.2.4.2.1 A GES-to-GES handover command could be
issued by the AES user in order to:
a) renew the log-on to the same GES but through a
different spot beam;
b) to switch the log-on to a different GES in the same
satellite service area, either through the same or a
different spot beam.
Such command may have to specify the GES ID and spot
beam ID when those IDS are different than the current values.
Circuit-mode calls in a Level4 AES (multiple transmit and
receive channel units) are not effected by the execution of this
command. Level-3 AES operation is as specified in Annex 10,
Volume III, Part I, Chapter 4, 4.9.3.3.4.2 b).
9.3.2.4.2.2 A satellite-to-satelli handover 'command
could be issued by the AES user in order to switch the AES
log-on to a new GES within the service area of another satellite.
Any circuit-mode call established through the current
satellite will have to be forcibly terminated after a fixed period
of time prior to switching to the new satellite. In the AMSS
SARPs, this period of time is set to 3 minutes. If the AES was
unable to tune to any of the listed satelliteheam-identifying
P, channels of the new satellite, the AES may revert back to
the previous satellite or any other satellite in view.
9.3.2.5 P channel loss/degradation
9.3.2.5.1 P channel loss/degradation declaration is
conveyed to the AES management in the form of an indication
from the AES physical layer (P channel receiver). The
criterion on which such declaration is based is given in Annex
10, Volume 111, Part I, Appendix A to Chapter 4. If the P
channel loss or degradation is caused by the aircraft flying out
of the selected beam coverage, the P channel loss/degradation
declaration will cause the AES management to search for a
new GES, within the same or a different satellite service area,
and log-on to it. However, the losddegradation of the P
channel would cause an undesirable discontinuity of both data
and voice services. Therefore, the use of such practice is not
advisable as a means to invoke an AES handover. The handover
commands described in Annex 10, Volume 111, Part I,
Chapter 4, 4.9.3.3.4.2 b) and c) provide a more controlled
means to invoke AES handovers.
9.3.2.5.2 Because all R and T channel transmissions are
synchronized to the framing format of the P channel, and in
order to ensure positive control of the AES from the GES,
such transmissions must cease with the loss of the P channel.
9.3.3 AES CHANNEL MANAGEMENT
9.3.3.1 Voice-voice pre-emption
9.3.3.1.1 Several circuit-mode calls could be contending
for the limited resources in the AES. In such cases. the establishment
and continuation of a circuit-mode call is regulated
by the priority and pre-emption requirement of Annex 10,
Volume 111, Part I, Chapter 4, 4.8.3.2 according to the precedence
of the Q number assigned to the C channels carrying the
calls. The C channels Q number assignment for the various
categories of voice transactions is given in Annex 10,
Volume Dl, Part I, Chapter 4, Table 4-43.
Annex 10 - Aeronautical Telecommunications Volume zzz
9.3.3.1.2 Various requirements are included in the
　
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