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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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packets that have been sent (PS). A sequence number (PS)
shall be assigned for each Mode S DATA packet generated by
the XDLP for each SVC. The first Mode S DATA packet
transferred by the XMJE to frame processing when the SVC
has just entered the flow control ready state shall be numbered
zero. The first Mode S packet received from the peer XDCE
after an SVC has just entered the flow control ready state shall
be numbered zero. Subsequent packets shall be numbered
consecutively.
5.2.6.4.4.2 A source of Mode S DATA packets (the
ADCE or GDCE) shall not send (without permission from the
receiver) more Mode S DATA packets than would fill the
flow control window. The receiver shall give explicit permission
to send more packets. .
5.2.6.4.4.3 The pimission information shall be in the
form of the next expected packet sequence number. and shall
be denoted PR. If a receiver wishes to update the window and
it has data to transmit to the sender, a Mvde S DATA packet
shall be used for infonnation transfer. If the window must be
updated and no data is to be sent, a Mode S RECEIVE
READY (RR) or Mode S RECEIVE NOT READY (RNR)
packet shall be sent. At this point, the "sliding window" shall
be moved to begin at the new PR value. The XDCE shall now
be authorized to transfer more packets without acknowledgement
up to the window limit.
5.2.6.4.4.4 When the sequence number (PS) of the next
Mode S DATA packet to be sent is in the range
PR 1 PS 1 PR + 14 (modulo 161, the sequence number shall
be defined to be "in the window" and the XDCE shall be
authorized to transmit the packet. Otherwise, the sequence
Part I Annex 10 - Aeronautical Telecommunicalions
number (PS) of the packet shall be defined to be "outside the
window" and the XDCE shall not transmit the packet to the
peer XDCE.
5.2.6.4.4.5 When the sequence number (PS) of the
packet received is next in sequence and within the window,
the XDCE shall accept this packet. Receipt of a packet with
a PS:
a) outside the window; or
b) out of sequence; or
c) not equal to 0 for the first data packet after entering
FLOW CONTROL READY state (dl);
shall be considered an error (512.6.8).
5.2.6.4.4.6 The receipt of a Mode S DATA packet with
a valid PS number (i.e. the next PS in sequence) shall cause
the lower window PR to be changed to that PS value plus 1.
5.2.6.4.5.2 The XDCE shall treat an S-bit sequence of
Mode S INTERRUPT packets as a single entity.
5.2.6.4.5.3 Interrupt processing shall have precedence
over any other processing for the SVC occumng at the time
of the interrupt.
5.2.6.4-5.4 The reception of a Mode S INTERRUPT
packet before the previous interrupt of the SVC has been
confirmed (by the receipt of a Mode S INTERRUPT
CONFIRMATION packet) shall be defined a an error.
5.2.6.5 RECEIVE READY PROCEDURE
5.2.6.5.1 The Mode S RECEIVE READY packet shall
be sent if no Mode S DATA packets (that normally contain
the updated PR value) are available for transmittal and it is
necessary to transfer the latest PR value. It also shall be sent
to terminate a receiver not ready condition.
The packet receive sequence number (PR) shall be conveyed
to the originating XDLP by a Mode S DATA, RECEIVE 5.2.6.5.2 Receipt of the Mode S RECEIVE READY
READY, REGENE NOT READY, or ~ E C pTack et, A packet by the XIXIE shall cause the XDCE to update its value
valid PR value shall be transmitted by the XDCE to the peer of PR for the outgoing SVC. It shall not be taken as a demand
XDCE after the receipt of 8 packets provided *hat sufficient for retransmission of packets that have already been transbuffer
space exists to store 15 packets. Incrementing the PR mitted and are in the windowand
PS fields shall be performed using modulo 16 arithmetic.
Note.- The loss of a packet which contains the PR value
may cause the ADLHGDLP operations for that SVC to cease.
5.2.6.4.4.7 A copy of a packet shall be retained until the
user data has been successfully transferred. Following successful
transfer, the PS value shall be updated.
5.2.6.4.4.8 The PR value for user data shall be updated
as soon as the required buffer space for the window (as
determined by flow control management) is available within
the DCE.
5.2.6.4.4.9 Flow control management shall be provided
between the DCE and XDCE.
5.2.6.4.5 INTERRUPT PROCEDURES FOR
SWITCHED VlRTUAL CIRCUITS
5.2.6.4.5.1 If user data is to be sent via the Mode S
subnetwork without following the flow control procedures, the
interrupt procedures shall be used. The intermpt procedure
shall have no effect on the normal data packet and flow
 
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