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must enable aircraji to exchange data with ground-based users.
Physical layerprotocol data unit (PPDU). Data unit passed to
the physical layer for transmission, or decoded by the
physical layer after reception.
Quality of service (QOS). The information relating to data
transfer characteristics used by various communications
protocols to achieve various levels of performance for
network users.
Reliable link service (RLS). A data communications service
provided by the subnetwork which automatically provides
for error control over its link through error detection and
requested retransmission of signal units found to be in
error.
11.1.1 Definitions Squitter protocol data unit (SPDU). Data packet which is
broadcast every 32 seconds by an HFDL ground station on
Coded chip. A "1" or "0" output of the rate % or !4 each of its operating frequencies, and which contains link
convolutional code encoder. management information.
Designated operational coverage (DOC) area. The area in
which a particular service is provided and in which the
service is afforded frequency protection.
Note.- This area may, afier proper co-ordination to ensure
frequency protection, extend to areas outside the allotment
areas contained in Appendix 27 to the Radio Regulations.
Direct link service (DLS). A data communications service
which makes no attempt to automatically correct errors,
detected or undetected, at the link layer of the air-ground
communications path. (Error control may be effected by
end-user systems.)
High frequency network protocol data unit (HFNPDU). User
data packet.
Link protocol data unit (LPDU). Data unit which
encapsulates a segment of an HFNPDU.
11.2 HF DATA LINK SYSTEM
11.2.1 System architecture
The HFDL system shall consist of one or more ground and
aircraft station sub-systems, which implement the HFDL
protocol (see 11.3). The HFDL system shall also include a
ground management sub-system (see 11.4).
11.2.1.1 AIRCRAFT AND GROUND STATION
SUB-SYSTEMS
The HFDL aircraft station sub-system and the HFDL ground
station sub-system shall include the following functions:
a) HF transmission and reception;
Media access protocol data unit (MPDU). Data unit which b) data modulation and demodulation; and
encapsulates one or more LPDUs.
c) HFDL protocol implementation and frequency selection.
M-ary phase shiff keying (M-PSK) modulation. A digital
phase modulation that causes the phase of the canier
waveform to take on one of a set of M values.
11.2.2 Operational coverage
M-PSK symbol. One of the M possible phase shifts of the
M-PSK modulated camer representing a group of log2 Frequency assignments for HFDL shall be protected
M coded chips. throughout their designated operational coverage (DOC) area.
Peak envelope power (PEP). The peak power of the Note 1.- Designated operational coverage (DOC) orens
modulated signal supplied by the transmitter to the antenna may be differentfrom current MWARAs or RDARAs as defined
transmission line. in Appendix 27 to the ITU Radio Regulations.
2511 VM
No. 79
ANNEX 10 - VOLUME III
Part I Annex 10 - Aeronautical Telecommunications
Note 2.- Additional co-ordination with ITU is required in Table 4-26 for message priorities 7 through 14, shall not
cases where DOC areas are not in conformity with the exceed the values of Table 11-1.
allotment areas specified in the ITU Radio Regulations.
Table 11-1. Transfer delays
11.2.3 Requirements for carriage of
HFDL equipment
Requirements for mandatory caniage of HFDL equipment
shall be made on the basis of regional air navigation
agreements that specify the airspace of operation and the
implementation time-scale.
The agreement above shall provide advance notice of at least
two years for the mandatory camage of airborne systems.
11.2.4 Ground station networking
11.2.4.1 Recommendation.- HFDL ground station
sub-systems should interconnect through a common ground
management sub-system.
Note.- This provides a distributed subnetwork, with a
subnetwork point of attachment (SNPA), depending on the
method of implementation, which allows for the maintenance
of virtual circuit connections as aircraft stations transition
between designated operational coverage areas. The
distribution may be multi-regional or world-wide.
11.2.5 Ground station synchronization
Synchronization of HFDL ground station sub-systems shall be
to within +25 ms of UTC. For any station not operating within
+25 ms of UTC, appropriate notification shall be made to all
aircraft and ground station sub-systems to allow for continued
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