WHY THE ATN IS GOOD FOR AOC APPLICATIONS
1 ATN eliminates the ASCII 8-bit character The 25-40 year old ACARS and MSGSW
oriented restrictions thereby permitting protocols are based on 8-bit ASCII encoding
bit-oriented applications at considerably rules which mix communications control
reduced recurring transmission costs. characters with data characters, severely
Every alphanumeric ASCII character limiting data transmission options. Bit values
requires 8 bits-on-the-wire. For example outside those defined for the upper and
"The quick brown fox jumps over 15 lazy lower case alphabet, and a few special
dogs back" is 48 ASCII characters or 384 characters become communications control
bits-on-the-wire. That same data can be characters that affect the data transmission
conveyed over the ATN using 4 bits to protocol. ARINC 622 gets around this
identify the fixed data, and 4 bits for the limitation by "high order 4-bit stuffing,"
variable portion (384 bits down to 8 bits). leaving only the lower 4 bits for data but
2 ATN eliminates the need for the costly The 25-40 year old ACARS and MSGSW
and complex (and largely failure prone) protocols have message size limitations built
multi-block segmentation and assembly in throughout. Huge investments have been
logic. made in the air and on the ground to
overcome these limitations with less than
3 ATN is highly reliable, and will likely The 25 year old ACARS protocol has no
eliminate the requirement for message message delivery assurance and poor
level acknowledgement thereby reducing transmission performance requiring a
the number of messages transmitted complex, sequence number based,
(less recurring costs), and minimizing application message acknowledgement
AOC application complexity (less one feature whereby separate or combined
time costs). application messages are exchanged to
trigger retrieval and/or housekeeping for
guaranteed message delivery.
4 ATN eliminates the need for a datalink The 25-40 year old ACARS and MSGSW
service provider (DSP) like ARINC or protocols are completely different,
SITA to perform value added (and costly) addressing mechanisms are virtually non-
protocol amalgamation, address existent, and data streams must be
gyrations, and message transformation manipulated and transformed between the
services. Remaining basic transmission air/ground and ground/ground segments.
and routing services are more likely to be With ATN, the airline host AOC application
available on the open has a direct connection (i.e., a telephone
telecommunications market. call) with each and every airborne AOC
application. Data streams arrive at the airline
host systems exactly as they leave the
aircraft, and vice versa. ATN has an
unlimited addressing hierarchy which
permits, as an example, unique addresses
for every seat on every aircraft.
5 With the elimination of the DSP value The current AOC application follows rigid
added message transformation services, rules wherein the use of specific
new applications such as weather labels/sublabels and formats must be strictly
graphics, and/or modifications to existing adhered to because the DSP community
applications, can be implemented more must be able to standardize message
quickly and for less money. Commercial- transformation services for all its airline
off-the-shelf (COTS), reasonably priced customers.
application products become an option.
6 Because ATN is based on ISO and ITU-T ACARS security and/or encryption
international standards, a considerable mechanisms are almost non-existent.
variety of economical, commercial-off- Because ACARS is not based on
the-shelf (COTS) encryption products are international standards, expensive products
readily available in the marketplace. must be custom designed.
7 ATN permits the use of commercial-off- Substantial savings immediately accrue
the-shelf (COTS) data compression through the several orders of magnitude
mechanisms like the DEFLATE algorithm reduction in the actual bits-on-the-wire. For
used in PKZIP. example, a standard uplinked flight plan
reduces from TBD to TBD.
8 ATN enables the direct filing of flight In today's environment, airlines use (and
plans, handling of NOTAMS, and use of pays for) a DSP to be its conduit to the FAA.
AFTN free text, without going through a Since the FAA is a State signatory to the
DSP. ICAO ATN SARPs, it stands ready to accept
direct ATN inputs from airlines, and to
generate ATN responses back to airlines.
9 ATN allows airlines to standardize on a The Collaborative Decision Making (CDM)
single, digital data communications decision to implement AOCNet was based
infrastructure replacing existing on the knowledge that airlines could, and
technologies like SLC Type B, AOCNet likely would, switch to ATN once it became
and others, and adding new capabilities available. Maintaining multiple datalink
like gatelink. technologies is both labor intensive, and
10 ATN enables airlines to gain competitive ATN will not be implemented worldwide at
advantages by permitting the rapid the same time. Airlines with the ability to
introduction of new applications and/or rapidly effect data communications based
modifications to existing applications. application changes will accrue benefits.
11 Both airlines and States acknowledge the Initial ATC datalink services are expected to
requirement for an ATN based digital be minimal with very small initial benefits,
data communications infrastructure to therefore, the airlines with smaller start up
anchor the "C" in CNS/ATM leading to a costs can benefit earlier - the FAA Builds 1
free flight. Forcing ATN to be linked solely and 1a (CM/CPDLC at en-route centers) are
to ATC applications risks its timely an example.
implementation due to large start-up