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时间:2010-07-21 23:17来源:蓝天飞行翻译 作者:admin
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for which some packets have been transmittcd shall be
deleted from the queue of DATA packets awaiting
transmission;
c) those Mode S DATA packets received Srom the peer
XDCE that are part of an incomplete M-bit sequence
shall bc discarded;
5.2.6.5.1 The Mode S RECEIVE READY packet shall be d) the lower window cdgc shall be set to 0 and the ncxt
sent if no Mode S DATA packets (that normally contain the packet sent shall have a sequence number (PS) of 0;
updated PR value) are available for transmittal and it IS
necessary to transfcr the latest PR value It also shall be sent e) any outstanding Mode S INTEKRUYI* packets to or
to terminate a receivcr not ready condition. from thc peer XDCE shall be left unconfirmed; and
5.2.6.5.2 Receipt of the Mode S RECEIVE READY f) any Mode S INTERRUPT packet awaiting transfer shall
packet by the XDCE shall cause the XDCE to update i ~vsa lue be discarded;
of PR for the outgoing SVC. It shall not bc taken as a demand
for retransmission of packets that havc already bcen g) data packets awaiting transfer shall not bc discarded
transmitted and are still in Ihc window. (unless thcy are part of a partially transfcrrcd M-bit
sequence); and
5.2.6.5.3 Upon receipt of he Mode S RECEIVE READY
packet, the XDCE shall go into be ADLP(GDLP) RECEIVE h) he transition to dl shall also include a transition to il,
READY state (gl j. j l , f l andgl.
Annex 10 - Aeronautical Telecornmt~nications Volume I11
5.2.6.7.2 The reset procedure shall apply to he DATA Tq Resequencing timers (see Tables 5-1 and 5-13)
TRANSFER state (p4). Thc error procedure in Table 5-16 associated with a specific SVC.
shall be followed. In any other slate the reset procedure shall
be abandoned. All operations involving the sequence number (SN) shall be
pcrCormed modulo 64.
5.2.6.9.2 Duplication window. The range of SNR values
5.2.6.8 REJECT PROCEDURE belween NESN - 32 and NESN - 1 inclusive shall be denoted
the duplication window.
5.2.6.8.1 When the XDCE receives a Mode S DATA
packet from the peer XDCE with incorrect format or whose 5.2.6.9.3 Resequencing window. The range of SNR values
packet sequence number (PS) is no1 within the defined window
between NESN + 1 and NESN + 31 inclusive shall be denoted
(Table 5- 19) or is out of sequence, il shall discard the received thc resequencing window. Received packets with a sequence
packet and send a Mode REJECT packet lo the peer XDCE
number value in this range shall be stored in the resequencing
via frame processing. The Mode S REJECT packet shall
window in sequence number order.
indicate a value of PR for which retransmission of the Mode
S DATA packets is to begin. The XDCE shall discard
subsequent out-of-sequence Mode S DATA packets whose 5.2.6.9.4 ~'~ANSMISSIOFNU NCTIONS
receipt occurs while the Mode S REJECT packet response is
still outstanding. 5.2.6.9.4.1 For each SVC, the first packet sent to establish
a connection (the first Mode S CALL REQUEST or first
5.2.6.8.2 When the XDCE receives a Mode S REJECT Mode S CALL ACCEPT packet) shall cause the value of the
packet from the peer XDCE, it shall update its lower window SN field to be initialized to zero. The value of the SN field
value with the new value of PR and begin to (re)transmit shall be incremented after the transmission (or retransmission)
packets wirh a sequence number of PR. of each packet.
5.2.6.8.3 Reject indications shall not be transferred to the 5.2.6.9.4.2 The maximum number of unacknowledged
DCE. If the IS0 8208 interface supports the reject procedures, sequencc numbers shall be 32 consecutive SN numbers.
the reject indications occurring on the IS0 8208 interface shall Should this condition be reached, then it shall be treated as an
not be transferred betwecn the DCE and the XDCE. error and the channel cleared.
5.2.6.9 PACKETR ESEQUENCING AND
DUPLICATE SUPPRESSION
Note I.- If rhe frames for an SVC include both types
(SLM and ELM), the sequence of packets may he lost due to
the different delivery times. The order may also be lost
nriiltiple interrogators are used to deliver frames for the same
SVC to a given XDLP The following procedure will correct for
a limited amount of desequencing.
Note 2.- This process serves as an inte@ace berween frame
processing and the XDCE function.
5.2.6.9.1 Rcsequencing. Resequencing shall be performed
independently for the uplink and downlink transfers of each
Mode S SVC. The following variables and parameters shall be
used:
SNR A 6-bit variable indicating rhe sequence number of
a received packet on a specific SVC. It is contained
in the SN field of the packcl (5.2.5.2.1.1.7).
NESN The next expected sequence number following a
 
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