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the phrase "aircraft DTE" will be used for the subnetwork
entity in an aircraft communicating with the station. A
subnetwork entity is a packet layer entity as defined in
IS0 8208.
Note.- The start of a burst may occur only at quantized
time intervals and this constraint allows the propagation delay
between the transmission and reception to be derived.
VDL Mode 4 DLS system. A VDL system that implements the
VDL Mode 4 DLS and subnetwork protocols to carry ATN
packets or other packets.
VDL Mode 4 specific services (VSS) sublayer. The sublayer
that resides above the MAC sublayer and provides VDL
Mode 4 specific access protocols including reserved,
random and fixed protocols.
VDL station. An aircraft-based or ground-based physical
entity, capable of VDL Mode 2, 3 or 4.
Note.- In the context of this chaptes a VDL station is also
referred to as a "station".
Vocoder. A low bit rate voice encoderldecoder.
Voice unit. A device that provides a simplex audio and
signalling interface between the user and VDL.
1/11/01
No. 76
Part l Annex 10 - Aeronautical Telecommunications
6.7.2 VDL Mode 3 SNDCF
6.7.2.1 The VDL Mode 3 shall support one or more of the
defined SNDCFs. The first is the standard ISO 8208 SNDCF
as defined in Doc 9705. This is a connection-oriented SNDCF.
The second type of SNDCF supported by VDL Mode 3 is
denoted fiame-based SNDCF. The details of this connectionless
oriented SNDCF are contained in the Manual on VDL
Mode 3 Technical Specifications, including network layer
interface, support for broadcast and unicast network packets,
and ATN router support.
Note.- The framed-based SNDCF is termed such because
it uses the VDL Mode 3 frames without the need for an
additional protocol (viz. IS0 8208 SNDCF) to transfer
network packets. The frame-based SNDCF achieves
independence from the network protocol by identrfying the
payload of each frame. Upon receipt of a frame, the payload
is examined and control is passed to the protocol identified.
6.8 VOICE UNIT FOR MODE 3
6.8.1 Services
6.8.1.1 The voice unit shall provide for a simplex,
"push-to-talk" audio and signalling interface between the user
and the VDL. Two separate mutually exclusive voice circuit
types shall be supported:
6.8.2 Speech encoding, parameters
and procedures
6.8.2.1 The VDL Mode 3 shall use the advanced
multiband excitation (AMBE) 4.8 kbitsls encodingldecoding
algorithm, version number AMBE-ATC-10, developed by
Digital Voice Systems, Incorporated (DVSI) for voice
communications.
Note I.- Information on technical characteristics of the
4.8 kbits/s AMBE algorithm is contained in AMBE-ATC-I0
Low Level Description, obtainable from DVSI.
Note 2.- The 4.8 kbits/s AMBE encoding/decoding
technology described in the document is subject to DVSI
patent rights and copyrights. Manufacturers must enter into a
license agreement with DVSI prior to obtaining a detailed
description of the algorithm before incorporation in equipment
operating in the VDL Mode 3 service. By letter to ICAO dated
29 October 1999, DVSI confirmed its commitment to license
the technology for the manufacture and sale of aeronautical
equipment under reasonable terms and conditions, negotiated
on a non-discriminatoly basis.
6.8.2.2 Speech encoding definition, voice unit parameters,
and procedure descriptions for VDL Mode 3 Voice Unit
operation are contained in the Manual on VDL Mode 3
Technical Specifications.
6.9 VDL MODE 4
a) Dedicated circuits: This shall provide service to a 6.9.1 A Mode 4 station shall conform to the requirements
specific user group on an exclusive basis with no defined in sections 6.1.2.3, 6.1.4.2, 6.2.1.1, 6.2.3.1, 6.2.4,
sharing of the circuit with other users outside the group. 6.3.1, 6.3.3.1, 6.3.4, 6.3.5.1, 6.3.5.2, 6.3.5.3, 6.3.5.4.1 and 6.9.
Access shall be based on a "listen-before-push-to-talk"
discipline.
6.9.2 VDL Mode 4 radio channels
b) Demand assigned circuits: This shall provide voice
circuit access which is arbitrated by the ground station
in response to an access request received from the 6.9.2.1 VDL MODE 4 STATION FREQUENCY RANGE
aircraft station. This type of operation shall allow
dynamic sharing of the channel resource increasing 6.9.2.1.1 Transmitter/receiver tuning range. A VDL
trunking efficiency. Mode 4 transmittertreceiver shall be capable of tuning to any
of the 25 kHz channels from 1 17.975 MHz through 137 MHz.
The transmitter shall have a means for the tuning range to be
6.8.1.2 Priority access. The voice unit operation shall restricted to a narrower range.
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