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application at the receiving end.
Aircrafl d r e s s . A unique combination of twenty-four bits
avilable for assignment to an aircraft for the puIpose of End-user. An ultimate source andlor consumer of infomation.
air-ground cammunications, navigation and surveillance.
Equivalent isotrtrpically radiated power (e. i.r.p) . The product
Aircraft eutth station (AES). A mobile earth station in the of the power supplied to the antenna and the antenna gain
aeronautical mobile-satellite service located on board an in a given direction relative to an isotropic antenna
aircraft (see also "GES"). (absolute or isotropic gain).
Bit error rate (BER). The number of bit errors in a sample Energyper symbol to noise density ratio (EiNd. The ratio of
divided by the total number of bits in the sample, the average energy transmitted per channel symbol to the
generally averaged over many such samples. average noise power in a I Hz bandwidth, usually
ANNEX 10 - VOLUME 111
7/11/96
No. 71
Annex 10 - Aeronautical Telecommunications Volume 111
expressed in dB. For A-BPSK and A-QPSK, one channel
symbol refers to one channel bit.
Fonvard error correction (FEC). The process of adding
redundant information to the transmitted signal in a
manner which allows correction, at the receiver, of errors
incurred in the transmission.
Gain-to-noise temperature raa'o. The ratio, usually expressed
in dB/K, of thc antenna g i n to the noise at the receiver
output of the antenna subsystem. The noise is expressed as
the temperature that a 1 ohm resistor must be raised to
produce the same noise power density.
Ground earth station (GES). An earth station in the fixed
satellite service, or, in some cases, in the aeronautical
mobile-satellite service, located at a specified fixed point
on land to provide a feeder link for the aeronautical
mobile-satellite service.
Note.- This defanition is ztsed in the ITU's Radio Regrrlations
under the term "aer~nauticale arth station." The definition
herein as "GES" for use in the SARPs is to clearly
distinguish it from an aircrafi earth station (AES), which is a
mobile station on an aircraft.
Mode S subnetwork. A means of performing an interchange
of digital data though the use of secondary surveillance
radar (SSR) Mode S interrogators and transponders in
accordance with defined protocols.
Packet. The basic unit of dala transfer among communications
devices within the network layer.
Packet layer protocol (PLP). A protocol to establish and
maintain a connection between peer level entities at the
network layer, and to transfer data packets between them.
In the context of this standard, the term refers to the
protocol defined by the IS0 8208 standard used in this
document.
Point-to-point. Pertaining or relating to the interconnection of
two devices, particularly end-user instruments. A communication
path of service intended to connect two
discrete end-users; as distinguished from broadcast or
multipoint service.
Slotted aloha. A random access strategy whereby multiple
users access the same communications channel independently,
but each communication must be confined to a
fixed time slot. The same timing slot structure is known to
all users, but there is no other co-ordination between the
users.
Switched vithral circuit (SVC). The primary circuit
management technique provided within the IS0 8208
protocol. The network resources are dynamically allocated
when needed and released when no longer required.
Time division multiplex (TDM). A channel sharing strategy in
which packets of information from the same source but
with different destinations are sequenced in time on the
same channel.
Time diviswn multiple access (TDMA). A channel sharing
strategy in which packets of information from different
sources and with the same or different destinations are
sequenced in time on the same channel.
Transit delay. In packet data systems, the elapsed time
between a request to transmit an assembled data packet
and an indication at the receiving end that the corresponding
packet has been received and is ready to be used
or forwarded.
VHF digital link (VDL). A constituent mobile subnetwork of
the aeronautical telecommunication network (ATN),
operating in the aeronautical mobile VHF frequency band.
In addition, the VDL may provide non-ATN functions
such as, for instance, digitized voice.
-611Y97
No. 72
CHAPTER 6. VHF AIR-GROUND DIGITAL LINK (VDL)
6.1 DEFINITIONS AND
SYSTEM CAPABILITIES
The VHF digital link (VDL) is a constituent mobile
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