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shall be maintained as floating-point values with a minimum
mantissa precision of 24 bits inclusive of a sign bit. The range
of the associated exponenl shall be such that the magnitude of
a positive or negative non-zero variable can vary over a
minimum range of 5.87747* to 3.40282*
minimum spectral characteristics. These characteristics may be
met by any combination of specific anti-aliasing filters andfor
the natural spectral roll-off characteristics of transducers and
audio channels:
Note.-- A11 specflcations are referenced to 1 020 Hz.
a) over a passband of 300 to 3 400 Hz; a gain variation of
no more than *2 dB;
b) over a transition band of 4 000 Hz to 4 600 Hz, a gain
of 4 5 dB or lower; and
C) at 4 600 Hz and above, a gain of -75 dB or lower.
Note 1.- In addition to the listed spectral characteristics,
additional filrering appropriate to the particular equipmenr
installarion should be provided in the low-end response
characteristics of the vocoder so as to mitigate the egects of
power supplv rroisc pickup (e.g. 400 Hz for AES installations
and 50/60 Hz for GES installations).
Note 2.- Ths input to the encoding algorithm is defined irz
3.2 fo be quantized audio samples with at least 12 bits of
resolution. Consequently, all required spectral chamcteristics
at the point of sampling are de$ned with this in mind. The use
of ti-law or A-law companded audio in conjunction with hotlz
reduced resolution (e.g. 8 bits) and appropriately relaxed
transition-band ard stop-band gain characteristics is
permitted provided that the quantized samples are
decompanded (linearized) prior to their presentation to the
algorithm.
Note.- Compliance with this minimum numeric range is
essential if interoperability between diflerent vocoder
implementations is to be ensured.
3. AUDIO INPUT
CHARACTERISTlCS
3.1 Audio input spectral
characteristics
Prior to sampling and quantization, speech audio which is
presented to the encoding algorithm shall exhibit the following * A11 figures are located at the end of this chapter.
198 ANNEX 10 - VOLUME III
Part Z Annex I0 - Aeronautical Telecommunications
process incoming information. A service primitive may
contairl parameters. If parameters exist, lhey describe
information that is defined either as mandatory (M) or
optional (0) for conformance to a particular communications
standard.
Service provider. An entity at a Iayer that provides services to
the layer above. These services are provided at service
access points through the use of service primitives.
Service user. An entity at a layer that makes use of the services
that are provided at service access points by the layer below
through the use of service primitives.
Subnetwork connection. A long-term association between an
aircraft DUE and a ground DUE using successive virtual
calls to maintain context across link handoff.
VDL station. A VDL-capable entity. A VDL station may
either be an aircraft station or a ground station. A VDL
station is a physical entity that transmits and receives
frames over the air-ground interface and comprises, at a
minimum: a physical layer, media access control sub-layer,
and a unique DLS address. The particular initiating process
(i.e. DLE or LME) in the VDL station cannot be
determined by the source DLS address. The particular
destination process cannot be determined by the destination
DLS address. These can only be determined by the context
of these frames as well as the current operational state of
the DLEs.
6.1.2 Radio channels and
functional channels
Subnetwork connection maintenance. The process by which 6.1.2.1 Aircraft station radio frequency range. An aircraft
the VDL SNXF maintains subnetwork context from one shall be capable of tuning to any of the 760 25-kH.Z channels
subnetwork connection to the next during handoffs. from 118.000 MHz through 136.975 MHz within 100 milliseconds
of the receipt of the autotune command.
Subnetwork connection management, The process by which
the VDL SNDCF initially establishes a comcction and then
maintains it during handoffs.
Subnetwork dependent convergence facility (SNDCF). A
facility that matches the characteristics and services of a
particular subnetwork to those characteristics and services
required by the internetwork facility.
Subnetwork entity. In this document, the phrase "ground
DCE" will be used for the subnetwork entity in a ground
station communicating with an aircraft; the phrase "ground
DTE will be used for the subnetwork entity in a ground
router communicating with an aircraft station; and, the
　
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