Wavecom W61PC V7.5.0 - Manual (Page 116)

106  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
the international airline data network - in fact much traffic previously carried by voice, has been trans-
ferred to ACARS.
The text field of the ACARS packet is used for messages with a fixed format, free text, or a mixture of
formatted and free text. Standard 7-bit ASCII is used; bit 8 is an odd parity bit and LSB (bit 1) is trans-
mitted first.
ACARS Downlink Message Example
(#8) 06-11-1996 18:43:32 M=06 ADDR= HB-INR TA=Q ML=Q0 B=6 MSN=0635 FID=SR6767
(Bold typeface indicates decoder generated characters)
Decoded Interpretation
(#8) Decoder generated message number
06-11-1996 18:43:32 Decoder generated timestamp (optional)
M= Mode Category A = A,
Category B = 0..29
ADDR= Aircraft address
(aircraft registration or flight identifier)
TA= Technical acknowledgement
(downlink 0...9, uplink A...Z, a...z, NUL (00h))
ML= Message Label (message type)
B= Uplink/Downlink Block Identifier
(downlink 0...9, uplink A...Z, a...z, NUL (00h))
MSN= Message Sequence Number
FID= Flight Identifier
In this case record #8 decoded at 18:43:32 contains a message from a Swiss aircraft with registration
HB-INR using logical channel 06 to transmit and acknowledgement of uplink block Q and a link test (Q0)
with block identifier 6 and message sequence number 0635 (here the time in minutes and seconds after
the hour is used - other formats are also in use). The flight is Swissair SR6767.
A few examples of the more important or frequently seen ACARS messages:
M=06 ADDR= HB-IND TA=NAK ML=_ B=3 MSN=2810 FID=OS005
Using logical channel 06 an unsolicited (TA=NAK) general response _ without information is transmitted
as block 3 from aircraft HB-IND on flight OS005 with sequence number 2810. General responses are
mainly used for block acknowledgement purposes.
M=06 ADDR= TA=NAK ML=SQ B= 00XSZRH
This is a "squitter" - an ID and uplink test message transmitted at regular intervals from ground stations.
This one is a squitter (SQ) version 0 (00) from a SITA (XS) ground station in Zurich, Switzerland (ZRH).
The denotes the ASCII NUL character (00h) used for broadcast. A block identifier is not used.
M=06 ADDR= OY-MDS TA=5 ML=:; B=131125
This is a data transceiver auto tune message (:;) from ground station 06 commanding the ACARS trans-
ceiver of aircraft OY-MDS to change its frequency to 131.125 MHz. At the same time acknowledgement is
given for the aircraft's downlink block 5.
AIS
AIS also known as (Universal) Automatic Identification System (UAIS) is a worldwide radio system for ship
collision avoidance and navigational advice. AIS-equipped ships continuously transmit short messages
containing information like position, course over ground, speed over ground, and so on. All information
may be sent from ship to ship, as well as well as from ship to shore. This is very useful for Vessel Traffic