IV Scan the text to decide if the sentences are true or false.

1 All ATC applications use the ACARS ground-ground link.

2 ICAO developed standards and recommended practices (SARPs) for the ATC.

3 It is intended to replace the AFTF, which has served the industry well as a

teletype-based, message-switching network for many years.

4 However, technology has overtaken AFTN, and the more modern packet-

switched technology of the ATN is seen as more appropriate.

5 The ATN SARPs development began in the early 2000s and, other than trial

implementations, has yet to be fully implemented.

6 In the past 13 years, the Internet, which is based on a different packet-switched

technology, i.e., TCP/IP, has had unprecedented success.

7 It may be necessary for ICAO to make some accommodation to TCP/IP lest the

cost of implementing the ATN be prohibitive.

8 As ACARS became essential to airline operations, the limitations of the initial

VHF link became tolerable, first because of coverage limitations and then

because of speed.

9 The former was solved in three different ways.

10 Long-range data link was implemented first using Inmarsat satellites; this was

not the basis for initial FANS implementations in the South Pacific.

11 The oceanic coverage provided by satellites and data link was not an

improvement over HF voice services.

12 All of the disadvantages of data link over voice communications were

highlighted in the initial FANS trials and operational use.

13 The disadvantages included: (a) consistent and rapid delivery of messages; (b)

standardized message texts, which were understood byall no matter what their

native language; (c) automated delivery of position reports.

14 HFDL provided another long-range ACARS subnetwork that covered the east

Polar Regions, which are not reached by Inmarsat signals.

15 VHF Digital Link (VDL) Mode 2 provided a higher-speed subnetwork in

continental airspace.

16 The ACARS avionics architecture is centered on the MU or CMU, which acts

as an onboard router.

17 All air-ground radios connect to the MU or CMU to send messages.

18 The CMU is connected to all of the various radios that communicate to the

ground.

19 The MU or CMU acts as the ACARS router onboard the aircraft.

20 All message blocks to or from the aircraft, over any of the air-ground sub

networks, pass through the CMU.

21 Although the MU handles all ACARS message blocks, it does not perform a

message-switching function because it does not recombine message blocks into

a “message” prior to passing it along.

22. In the modern transport aircraft, many other avionics units send and receive

routine ACARS messages.

23 The MCDU, along with the printer, is the primary ACARS interface to the

ground crew.

24 The original VHF subnetwork that was pioneered in 2000 uses the same 25

kHz VHF channels used by ATC and AOC voice.

25 The VHF subnetwork uses a form of frequency shift keying (FSK) called

minimum shift keying (MSK) wherein the carrier is modulated with either a

1200 Hz or 2400Hz tone.

26 Each signaling interval represents one bit of information, so the 2400 baud rate

(i.e., rate of change of the signal) equals the bit rate of 2400 BPS.

27 After initial synchronization, the receiver then can determine whether a given

bit is a one or a zero.

28 VHF ACARS uses the CSMA protocol to reduce the effects of two transmitters

sending a data block at the same or overlapping times.

29 CSMA is nothing more than the automated version of voice radio protocols

wherein the speaker first listens to the channel before initiating a call.

30 The VHF ACARS subnetwork is an example of a connectionless link layer

protocol in that the aircraft does not “log in” to each ground station along its

route of flight.

31 The aircraft does initiate a contact with the central message processor, and it

does transmit administrative message as it changes subnetworks.