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filled with zeros. Where the channel rates are implemented as
defined in 4.1.3, at the channel rate of 5.25 kbitsts each
subfield shall contain 4 sub-band data bits and 96 primary bits:
the last 4 bits of the 25th sub-band data subfield shall be filled
with zeros.
Note.- Interleaving is not applicable at the channel rates
of 10.5 and 5.25 kbits/s because the data is not forward error
correction coded at these rates.
4.4.5.4 Performance. The C channel physical layer shall
be configured and operated such that the average bit error rate
is or less after descrarnbling.
Note.-- GES measurements of received BER permit GES
commands to the AES for adjustment of the AES transmitted
power The GES also receives pe$onnance data measurement
results made by the AES to enable GES output power
adjustments.
4.5 LINK LAYER P CHANNEL
AND R CHANNEL PROTOCOLS
4.5.1 General
Note.- The AMSS protocols are defined in terms of the OSI
layered reference model. Section 4.5 defines the functional
requirements of the link layer for P and R channels to transfer
user data and signalling between the AES and the GES.
4.5.1.1 For each AES and GES, the link layer shall
interface to the following:
a) the subnetwork layer;
b) the AESIGES management;
c) the circuit-mode services;
d) the physical layer.
4.5.1.2 The term link service user when used with respect
to the link layer in 4.5 shall include items a), b) and c) in the
list above.
4.5.2 Link interface data
unit (LIDU)
4.5.2.1 The link interface data unit (LIDU) shall be the
total information unit transferred across the interface between
the link service user and the link layer in a single interaction.
Each LIDU shall comprise link interface control information
(LICI) and, if required, one LSDU.
4.5.2.2 The LIDU exchanged between the link layer and
the subnetwork layer shall contain an LSDU and LICI, except
that the transmission status indication LIDU (Table 4-25)
passed by the link layer to the subnetwork layer at the
transmitting end shall contain only LICI. The LDU exchanged
between the link layer and thc AESIGES management and
between the link layer and the circuit-mode services shall
contain only LICI.
4.5.2.3 LINK INTERFACE CONTROL
INFORMATION (LICI)
4.5.2.3.1 The LICI parameters exchanged between the
link layer and the subnetwork layer shall be as defined in Table
4-11.
4.5.2.3.2 The LICI parameters exchanged between the
link layer and the circuit-mode services shall be as defined in
Table 4-38.
4.5.2.3.3 The LICI parameters exchanged between the
link layer and the AES and GES management functions shall
be as defined in 4.9.2.1.2 and Table 4-45, respectively.
4.5.2.4 LINK SERVICE DATA
UNIT (LSDU)
Note.- The link service data unit (LSDU) is a part of an
LIDU whose identity is preserved between the two link service
users communicating with each othet:
4.5.2.4.1 The link service data unit (LSDU) shall contain
link service user data and shall be extracted from the LDU
received from the subnetwork layer.
4.5.2.4.2 LINK SERVICE DATA
UNl T FORMAT
The LSDU format shall be the same as the format of satellite
subnetwork protocol data units (SNPDUs) in the SSND sublayer
described in 4.7.
2/lVOO
No. 75
Annex 10 - Aeronautical Telecommunications Volume 111
4.5.3 Link protocol data
unit (LPDU)
4.5.3.1 The link protocol data units (LPDUs) shall be the
signal units (SUs) described in 4.5.3.2.
4.5.3.2 SIGNALUN IT (SU)
4.5.3.2.1 There shall be two lengths of SUs for the P and
R channels:
a) 96 bits (12 octets): standard length SUs for P channel;
b) 152 bits (19 octets); extended length SUs for R channel.
4.5.3.2.2 Each SU shall contain control information, and
may include user data depending upon the SU type.
4.5.3.2.3 LDU-TO-SU SET MAPHNG
4.5.3.2.3.1 Each LDU received by the link layer, before
being transmitted to the peer link layer, shall be mapped into
an SU set. Each SU set shall, comprise either a single signal
unit called a "lone signal unit" (LSU) or more than one signal
unit of which the first shall be an "initial signal unit" (ISU)
and those that follow shall be "subsequent signaj units"
(SSUs).
4.5.3.2.3.2 For LIDU comprised of
LSDU and LlCI
4.5.3.2.3.2.1 For the P channel, an LSDU of length 2, 3 or
4 octets shall be mapped into standard length LSUs of Figures
A2-37, A2-39 and A2-40 in Appendix 2 to Chapter 4,
respectively. An LSDU of length greater than 4 octets, shall
result in an ISU followed by a maximum of 63 SSUs. For an
 
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