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sublayer resides above the VSS sublaycr. The DLS
manages the transmit queue, creates and destroys DLEs for
connection-oriented communications, provides facilities for
the LME to manage the DLS, provides facilities for
connectionless communications.
Data terminal equipment (DTE). A DTE is an endpoint of a
subnetwork connection.
Extended Golay Code. An error correction code capable of
correcting multiple bit errors.
Frame. The link layer frame i s composed of a sequence of
address, control, FCS and information fields. For VDL
Mode 2, these fields are bracketed by opening and closing
flag sequences, and a frame may or may not include a
variable-length information field.
Gaussian filtered frequency shift keying (GFSK). A
continuous-phase, frequency shift keying technique using
two tones and a Gaussian pulse shape filter.
Global signalling channel (GSC). A channel available on a
world-wide basis which provides for communication
control.
Link. A link connects an aircraft DLE and a ground DLE and
is uniquely specified by the combination of aircraft DLS
address and the ground DLS address. A different
subncrwork entity resides above every link endpoint.
Link layer. The layer that lies immediately above the physical
layer in the Open Systems Interconnection protocol model.
The link layer provides for the reliable transfer of information
across the physical media. It is subdivided into the
data link sublayer and the media access control sublayer.
Link management entity (LME). A protocol state machine
capable of acquiring, establishing and maintaining a
connection to a single peer system. An LME establishes
data link and subnetwork connections, "hands-off' those
connections, and manages the media access conwol
sublayer and physical layer. An aircraft LME tracks how
well it can communicate with the ground stations of a
single ground system. An aircraft VME instantiates an
LME for each ground station that it monitors. Similarly, the
ground VME instantiates an LME for each aircraft that it
monitors. An LME is deleted when communication with
the peer systcm is no longer viable.
M burst. A management channel data block of bits used in
VDL Mode 3. This burst contains signalling information
needed for media access and link status monitoring.
ANNEX 10 - VOLUME III 1/11/01
No. 76
Annex 10 - Aerorzautical Telecummurzicatiorzs Volume III
Media access control (MAC). The sublayer that acquires the
data path and controls the movement of bits over the data
path.
Mode 2. A data-only VDL mode that uses DSPSK modulation
and a camer sense multiple access (CSMA) control
scheme.
Mode 3. A voice and data VDL mode that uses DSPSK
modulation and a TDMA media access co~ltrols cheme.
Mode 4. A data-only VDL mode using a GFSK modulation
scheme and self-organizing time division multiple access.
Subnetwork layer. Thc layer that cstablishcs, manages and
terminates connections across a subnetwork.
System. A VDL-capable entity. A system comprises one or
more stations and thc associated VDL management entity.
A system may either be an aircraft system or a ground
system.
Time division multiple access (TDMA). A multiple access
scheme based on time-shared use of an W channel
employing: (1) discrete contiguous time slots as the
fundamental shared resource; and (2) a set of operating
protocols that allows users to interact with a master control
station to mediate access to the channel.
Physical layer. The lowest level layer in the Open Systems
Interconnection protocol model. The physical layer is User group. A group of ground andor aircraft stations which
concerned with the transmission of binary information over share voice andor data connectivity. For voice communithe
physical medium (e.g. VHF radio). cations, all members of a uscr group can access all
communications. For data, communications include
point-to-point connectivity for air-to-ground messages, and
Quality of service. The information relating to data transfer point-to-point and broadcast connectivity for ground-to-air
characteristics used by various communication protocols to messages.
achievc various levels of performance for network users.
VDL management entity (VME). A VDL-specific entity that
Reed-Solomon code. An crror correction code capable of provides Lhe quality of service requested by the ATNcorrecting
symbol errors. Since symbol errors are dcfined SN-SME. A VME uses t h ~LM Es (that i~ crcates
collections of bits, thcsc codes provide good burst error and destroys) to enquire thc quality of service available
correction capabilities. from peer systems.
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