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时间:2010-07-21 22:59来源:蓝天飞行翻译 作者:admin
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services interface (5.2.3.2.2).
5.2.7.3.2 Long form MSP packet. The format for this
packet shall be as follows:
Fields shown in the packet format Ad not specified in the
following paragraphs shall be set as specified in 5.2.5.2.1 and
5.2.7.3.1.
5.2.7.3.3 Data packet type (DP). This field shall be set
to 0.
5.2.7.3.3.1 MSPpncket lype (MP). This field shall be set
to 1.
5.2.7.3.3.2 Supervisory packet (SP). This field shall be
set to 0.
5.2.7.3.3.3 L3eld (L). A value of 1 shall indicate that
the packet is part of an L-bit sequence with more packets in
the sequence to follow. A value of 0 shall indicate that the
sequence ends with this packet.
5.2.7.3.3.4 MSP sequence number field (M/SN). This
field shall be used to detect duplication in the delivery of L-bit
sequences. The first packet in an L-bit sequence shall be
assigned a sequence number of 0. subsequent packets shall bc
numbered sequentially. .A packet received with the same
sequence number as the previously received packet shall be
discarded.
5.2.7.4 L-bit processing. L-bit processing shall be
performed only on the long form MSP packet and shall be
performed as specified for M-bit processing (5.2.5.1.4.1)
except as specified in the following paragraphs.
5.2.7.4.1 Upon receipt of a long form MSP packet, the
XDLP shall construct the user data field by:
a) verifying that the packet order is correct using the
MISN field (5.2.7.3.2):
b) assuming that the user data field in the MSP packet is
the largest number of integral bytes that is contained
within the frame;
Annex 10 - Aeronautical Telecommunications Volume ZIT
C) associating each user data field in an LMSP packet
received with a previous user data field in an MSP
packet that has an L-bit value of 1;
d) truncating the assembled user data field to 151 bytes
(in the ADLP) and 159 bytes (in the GDLP) if
necessaq; and
Note.- Tri4ncatiort of the user data field is a condition
that cannot be reported.
e) if an error is detected in the processing of an MSP
packet, the packet shall be discarded.
5.2.7.4.2 In the processing of an L-bit sequence, the
XDLP shall discard any MSP packets that have duplicate
M/SN values. The XDLP shall discard the entire L-bit
sequence if a long form MSP packet is determined to be
missing by use of the MISN field.
5.2.7.4.3 The packets associated with any L-bit sequence
whose reassembly is not completed in Tm seconds (Tables 5-1
and 5-13) shall be discarded,
5.2.7.5 Broadcastformat. The first byte of the broadcast
MA field shall contain the broadcast identifier as specified in
Table 5-23.
5.2.8 Mode S subnetwork management
5.2.8.1 INTERROGATOR LINK
DETERMINATION FUNCTION
Note.- The ADLP interrogator link determinatiortfunction
selects the II code of the Mode S interrogutor through which
a Mode S subnetwork packet may be routed to the desired
destination ground DTE.
5.2.8.1.1 11 code-DTE address correlation. The ADLP
shall construct and manage a Mode S interrogator-data
terminal equipment (DTE) cross-reference table whose entries
are Mode S interrogator identifier (11) codes and ground DTE
addresses associated with the ground ATN routers or other
ground DTEs. Each entry of the I1 code-DTE cross-reference
table shall consist of the 4-bit Mode S I1 code and the 8-bit
binary representation of the ground DTE.
Note I.- Due to the requirement for non-ambiguous
addresses, a DTE address also uniquely identifies a GDLP
Note 2.- An ATN muter may have more than one ground
DTE address.
5.2.8.1.2 Protocol. The following procedures shall be
used:
a) when the GDLP initialIy detects the presence of a data
link-equipped aircraft, or detects contact with a
currently acquired aircraft through an interrogator with
a new I1 code, the GDLP shall uplink one or more
Mode S ROUTE packets as specified in 5.2.5.3.3.. This
information shall relate the Mode S interrogator identifier
(11) code with the ground DTE addresses accessible
through that interrogator. The ADLP shall update
the I1 code-DTE cross-reference table and then discard
the Mode S ROUTE packet(s);
b) a II code-DTE cross-reference table entry shall be
deleted when commanded by a Mode S ROUTE
packet or when the ADLP recognizes that.the transponder
has not been selectively interrogated by a
Mode S interrogator with a given I1 code for Ts
seconds by monitoring the IIS subfield in Mode S
surveillance or Comm-A interrogations (Table 5- 1);
c) when the GDLP determines that modification is
required to the Mode S interrogator assignment, it
 
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