-Manual: a service provider region is selected on VHF3 DATA MODE page
-Scan mode: when no communication with the ground is established using the current service provider, the ATSU starts scanning the list of service providers selected in the VHF3 scan mask and displayed in the VHF3 DATA MODE page
-Remote: change of frequency on reception of an autotune uplink message (label ":;").
(b)
VHF SCAN MASK (Ref. Fig. 003B) The VHF scan mask selected on the VHF3 SCAN MASK page is displayed on the VHF3 DATA MODE page where the crew selects the service provider to be scanned. The VHF3 SCAN MASK is compulsory for the router operation. For all frequency acquisition methods, except autotune method, only the frequencies acceptable by the airline (DSP contracted by the airline) are used by the Router. A specific table called "VHF scan mask" lists the service providers contracted by the airline (no frequency information stored in this table). This table is used by the Router in manual and scan modes to scan only on the contracted service providers.
1_ Service Providers
In manual mode, the Router scans on a specific service
provider region.
The ATSU uses this information to retrieve internally the
frequency.
There are twelve world service providers:
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DSP Frequency --------------------------------------------------SITA Europe 131.725 MHz SITA USA 136.850 MHz SITA Pacific 131.550 MHz ARINC EUROPE 136.925 MHz ARINC USA 131.550 MHz ARINC South America 131.550 MHz ARINC KOREA 131.725 MHz AVICOM 131.450 MHz AIR CANADA 131.475 MHz DEPV Brazil 131.550 MHz AEROTHAI Thailand 131.450 MHz ADCC China 131.450 MHz
NOTE : The ATSU permanently reports to the crew, via the VHF3
____ DATA MODE page, the SP region it is operating on.
(6) DSP USER DEFINED 1 and 2 Two MCDU pages called DSP USER-DEFINED1 and DSP USER-DEFINED2 enable the airline to customize two more service providers. To do that, the crew enters the password "NEW DSP" in the MCDU scratchpad of the VHF3 SCAN MASK page 2/2 and presses the line select key 2R to define the DSP USER-DEFINED1 or 3R to define the DSP USER-DEFINED2.
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(7) Data Exchange operation
-
The ATSU configures the VDR3 in ARINC 750 protocol.
-
The ATSU sends ARINC 618 blocks in digital format to the VDR3 (VHF data parameters such as data frequency, aircraft addresses).
-
The VDR3 adds the VHF protocol overhead and performs the modulation on the VHF signal
-
The VDR3 demodulates the received VHF signal and sends the received blocks to the ATSU in digital format.
-
The ATSU controls the VHF operational parameters of the VDR3 (frequency...).
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(8) Uplink messages processing The ATSU router receives messages from the VDR3 and SDU (if installed). All uplink blocks other than squitters (label SQ) and whose address fields (airline ID and ARN) do not match the aircraft addresses are ignored. Uplink messages are processed either by the ATSU router or directed to the appropriate hosted application or remote AOC peripherals, according to the message label/sublabel:
SQ Message Squitter
:; Remote autotune
_DEL General response
54 Voice Go-ahead
C1 Printer message
Messages with label H1 are directed to the remote AOC applications.
The ATSU generates the green left memo "ACARS CALL" when the uplink
message is a Voice Go-ahead message (label 54).
Sublabels enable to direct the message to the appropriate peripheral:
H1/M1 FMGC1 H1/M2 FMGC2 H1/MD FMGC Master H1/CF CFDIU H1/DF DMU (ACMS) H1/T1 Cabin Terminal 1 H1/T2 Cabin Terminal 2
Other labels are directed to hosted AOC applications.
(9) Downlink messages processing All downlink messages are sent to the VDR3 or the SATCOM by the ATSU. A routing policy lists a set of allowed media, with a preference order and the conditions which lead to a change of medium. The routing policy are "V" for VHF only, "S" for SATCOM and "G" for ground (VHF or SATCOM if available). Routing policies are customizable for hosted AOC applications. The AOC routing policy table used by the ATSU defines:
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