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时间:2010-07-20 23:46来源:蓝天飞行翻译 作者:admin
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of each packet.
5.2.6.9.4.2 The maximum number of haacknowledged
sequence numbers shall be 32 consecutive SN numbers. When
this condition is reached, all further SVC packets far that
channel shall be held by the XDLP until acknowledgment of
successful delivery is received from the connected interrogator(~)
o r transponder for the oldest packet in transit.
Note.- A limit on the number of unacknowledged packets
is required since the SNfield is six bits lorig and therefore has
a muxlmuna of 64 difSerent values before the values repeat.
5.2.6.9.5 RECEWE FUNCTIONS
5.2.6.9.5.1 Resequencing. The resequencing algorithm
shall maintain the variables HSNR and NESN for each SVC.
NESN shall be initialized to 0 for all SVCs and shall be reset
to 0 when the SVC re-enters the channel number pool
(5.2.5.1.2).
5.2.6.9.5.2 Processing of packets within the duplication
window. If a packet is received with a sequence number value
within the duplication window, the packet shall be discarded.
5.2.6.9.5.3 Processing of packets within the resequencing
wiridow. If a packet is received with a sequence number
within the resequencing window, it shall be discarded as a
duplicate if a packet with the same sequence number has
already been received and stored in the resequencing window.
Otherwise, the packet shall be stored in the resequencing
window. Then, if no Tq timers are running, HSNR shall be set
to the value of SNR for this packet and a Tq timer shall be
started with its initial value (Tables 5-1 and 5-13). If at least
one Tq timer is running, and SNR is not in the window
between NESN and HSNR + 1 inclusive, a new Tq timer shall
be started and the value of HSNR shall be updated. If at least
one Tq timer is running, and SNR for this packet is equal to
HSNR + 1, the value of HSNR shall be updated.
5.2.6.9.5.4 Release of packets to the XDCE. I f a packet
is received with a sequence number equal to NESN, the
following procedure shall be applied:
a) the packet and any packets already stored in the
resequencing window up to the next missing sequence
number shall be passed to the XDCE;
b) NESN shall be set to 1 + the value of the sequence
number of the last packet passed to the XIICE; and
c) the Tq timer associated with any of the released
packets shall be stopped.
Part I Annex 110 - Aeronauticnl Tebcommunications
5.2.6.9.6 Tq timer expiration. If a Tq timer expires, the
following procedure shall be applied:
a) NESN shall be incremented until the next missing
sequence number in the resequencing window is
detected;
b) any stored packets with sequence numbers that are no
longer in the resequencing window shall be forwarded
to the XDCE except that an incomplete S-bit sequence
shall be discarded; and
c) the Tq timer associated with any released packets shall
be stopped.
5.2.7 Mode S specific services processi~ig
Mode $ specific services shall be processed by an entity in the
XDLP termed the Mode S specific services entity (SSE).
Note 1.- This section describes the processing of control
and message data received from the Mode S specific services
inte$ace.
Note 2.- Conrrol dara consists of information permitting
the determination oj for example,. message length, GICB
register number atad aircraft address.
5.2.7.1 ADLP PROCESSING
5.2.7.1.1 DOWNLINK PROCESSING
5.2.7.1.1.1 Specific services capability. The ADLP shall
be capable of receiving control and message data from the
Mode S specific services interface(s) and sending delivery
notices to this interface. The control data shall be processed to
determine the protocol type and the length of the message
data. When the message or control data provided at this
interface are erroneous (i.e. incomplete, invalid or inconsistent),
the ADLP shall discard the message and deliver an
error report at the interface.
Note.- The diugnostic content and error reporting
mechanism are a local issue.
5.2.7.1.1.2 Broadcast processing. The 7-byte broadcast
message content (5.2.7.5) shall be extracted from the received
message data. The broadcast message content shall be used to
specify the MB field of a Comm-B broadcast messagc and
transferred to the transponder. The assignment of downlink
broadcast identifier numbers shall be as specified in
Table 5-23.
Note.- The downlink broadcast identifier is equivulent to
the Comm-B data selector (BDS) value (3.1.2.6.11.2.1 of
Annex 10, Volunze IV).
5.2.7.1.1.3 GlCB processing. The 8-bit GICB register
number shall be determined from the control data. The 7-byte
GICB register content shall be extracted from the received
 
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