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时间:2010-07-20 23:38来源:蓝天飞行翻译 作者:admin
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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.
45.2 Link interface data
unit &IDU)
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 LIDU exchanged
between the link layer and the 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- 4-1 1.
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 (UDUj is a part of an
LIDU )chose identiiy is preserved between the two link sendce
users cornrnun,icating With each other.
4.5.2.4.1 The link service data unit (LSDU) shall contain
link service user data and shall be extracted from the LIDU
received from the subnetwork layer.
4.5.2.4.2 LINK SERVICE DATA
Lrh'1T 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.
453 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 SIGNAL UNIT (SU)
4.5.3.2.1 There shall be two lengths of SUs for the P
and R channels:
a) 96 bits (1 2 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 UDU-TO-su SET MAPPlNC
4.5.3.2.3.1 Each LIDU 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 signal units"
(SSUs).
4.5.3.2.3.2 For LlDU comprised of
LSDU and LICI
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
LSDU of length greater than 4 octets, the first two octets of
the LSDU shall be mapped into the Zoctet user data field of
an ISU (Appendix 2 to Chapter 4, Figure A2-37). The remaining
octets shall be mapped into the 8-octet user data fields of
subsequent SSUs (Appendix 2 to Chapter 4, Figure A2-38)
ordered by sequence numbers (Appendix 3 to Chapter 4, Item
59). The number of SSUs shall depend upon the number of
octets in the LSDU. The control information in each SW of the
Annex 10 - Aeronautical Telecommunications
SU set shall be mapped from the information contained in the
LICI and the information generated by the internal link layer
protocol processes.
Note.- Each ISU contains information indicating the
number of octets in the user data jield of the last SSU of the
SU set.
4.5.3.2.3.2.2 For the R channel, an LSDU shall map into
a maximum of 3 extended length SUs, with the ISU of the SU
set containing the first 11-octets (Appendix 2 to Chapter 4,
Figure A2-44) of the LSDU in its user data field. The
remaining octets shall be mapped into the I 1-octet user data
field of SSUs ordered by sequence indicator (Appendix 3 to
Chapter 4, Item 58). The control information in each SU of
the SU set shall be mapped from the information contained in
 
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