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R  number of its system table with that of the one being received 
R  from the logged on GES. According to the content of the updated 
R  system table, the AES may re-select the satellite at this point. 
R  Then, after selection of a Pd frequency, the AES selects a GES 
R  according to frequency specified in the ORT or at random from the 
R  system table and whether the GES is operating a Pd-Channel in the 
R  spot beam where the AES is located. The GES identifies the AES by 
R  its technical address and registers the AES as operational in 
R  that region. At this point the AES is considered to be logged 
R  onto the system. 
R 
R  NOTE : Each GES monitors P-Channel transmissions of every other____ 
R  GES in the same satellite region. Thus, when an AES logs 
R  onto a GES, the other GES's in that region also note its 
R  presence. This feature assists in the completion of 
R  connections for ground-initiated calls to aircraft 
R  operating in that satellite region. It also allows an AES 
R  to place a call through a GES other than the one to which 
R  it is logged on.

 

R 
R  (b) Call initiation 
R 
R  1 Air-to-ground calls_ 
R 
R  When a call is initiated by an airbone subscriber, the AES 
R  sends signals to the GES, using the Rd-Channel. When the GES 
R  receives the call request, it assigns a pair of C-Channels, 
R  for a voice call, or reserves time on a T-Channel, for 
R  long-duration data transmissions. The call can then go 
R  through. 
R  The assigned channels are reserved for as long as the call is 
R  in progress. The sequence used to initiate the call is 
R  automatic and transparent to both the originator and the 
R  receiver of the call. 
R 
R  2 Ground-to-air calls_ 
R 
R  The installed cabin system does not allow to establish 
R  ground-to-air calls. Moreover calls initiated from the ground 
R  are currently not allowed for safety reasons. 
R 
R  (c) Log-on renewal 
R 
R  If degradation or loss of the P-Channel is detected by the AES 
R  after log-on, the AES attempts to re-establish communication with 
R  its logged on GES. 
R  The AES uses the assigned Pd/Rd frequencies to renew log-on, but 
R  if this fails, the AES tunes to the Psmc and Rsmc frequencies of 
R  the logged on GES and tries to log-on again. If the Psmc 
R  frequency is satisfactorily received within 10 seconds, then 
R  log-on to the same GES is renewed. 
R  If the Psmc frequency is not received within 10 seconds, then the 
R  SDU tunes to the Psmc frequency of the next preferred GES. The 
R  AES initiates a handover log- on procedure with this GES if its 
R  Psmc frequency is successfully received within 10 seconds. If the 
R  Psmc frequency of the next preferred GES is not received within 
R  10 seconds, the AES deems itself logged off but does not transmit 
R  a log-off request. Then the AES reverts to a satellite search 
R  procedure. During log on renewal in the same satellite region, 
R  the flight information is not transmitted with the log-on 
R  request. 
R

 

R  (d) Handover 
R 
R  1_  Automatic handover
R 
R  Automatic handover is initiated upon detection of Pd-Channel 
R  link degradation, which is defined as the error rate rising 
R  above 10 to the power of -4 over an averaging period of three 
R  minutes, or more than 10 short term interruptions in any 
R  three-minute period. Automatic handover is also initiated upon 
R  detection of loss of Pd-Channel, which is defined as clock 
R  synchronization for more than 10 seconds, and the resulting 
R  log-on renewal procedure is unsuccessful. 
R 
R  2_  GES-GES handover
R 
R  A GES to GES handover is carried out by logging on to a new 
R  GES in the same satellite region. The AES carries out a log on 
R  procedure to the new GES. 
　
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