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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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AES may be processing the transmission of several LSDUs
(reference number is assigned and an SU set is generated from
each LIDU to transmit the LSDU). However, for RLS, at each
Q number only one LSDU is permitted to be in process for
transmission to the GES at one time. Other RLS LSDUs with
the same Q number will be stored in the AES until the transmission
of the current RLS LSDU at that Q number is over,
either successfully or unsuccessfully. Thus, at the GES, only
one RLS SU set per Q number per AES could be in the
reassembly process at a given time and the GES will discard
an incomplete RLS SU set if it starts receiving another RLS
SU set with the same Q number from the same AES. After
either a successful or an unsuccessful transmission of an SU
set, the AES link layer releases all link layer resources
associated with that SU set, i.e. the assigned reference number,
activated timers, memory allocation, etc.
5.5.4 For RLS, the R channel protocol implements a
selective-repeat-ARQ scheme for error control. Accordingly,
upon transmitting an SU set, the AES expects to receive an R
channel acknowledgement (RACK) SU from the GES. The
RACK SU may indicate either complete or incomplete reception
using its acknowledgement control field. In the latter case,
the RACK SU also indicates the missing SUs of the SU set by
identifying their sequence indicators. The AES transmits the
indicated missing SUs without any alterations to their contents.
The largest SU set on the R channel contains three SUs, thus,
the GES may identify at the most two missing SUS in a
RACK SU, one SU of the set must be correctly received at the
GES in order to detect an attempt of an SU set transmission.
Amhment A to Purt I Annex 10 - Aero~uticulT eIecommunicolions
5.5.5 The R channel is a multiple access channel,
therefore, the GES concurrently receives SUs from all AES
assigned to one set of R channel frequencies. Each received
SU contains the source AES ID. Thus, the received SUs are
first sorted out according to their AES IDS and then
independently processed. Annex 10, Volume U1, Part 1,4.5.8.3
contains the R channel protocol requirements corresponding to
the processing of SUs from a given AES.
6. LINK LAYER T CHANNEL AND
SUB-BAND C CHANNEL PROTOCOLS
6.1 General
The link layer T channel protocols specified in Annex 10,
Volume DI, Part I, Chapter 4,4.6 applies to link service data
units (LSDUs) in the from-aircraft direction which cannot be
transmitted via the R channel (e.g. because its length exceeds
33 octets). There are two T channel protocols: one for
requesting the T channel capacity and the other for the
transmission of SUs in assigned capacity. The link layer subband
C channel protocol specified in Annex 10, Volume 111,
Part I, Chapter 4,4.6 applies to the transmission of signalling
SUs corresponding to the circuit-mode services in the toaircraft
and from-aircraft directions.
6.2 SU set generation
An SU set cannot be generated from the received LIDU as
described in Annex 10, Volume El, Part I, Chapter 4,4.6.4.2.1
until a reference number is assigned to it by the T channel
reservation pmtocol, The LSDU (used data) is encoded in the
user data field of the ISUtSSU of a T channel SU set. The
number of SUs needed in the SU set depends on the LSDU
length. Each SU, except the last one, will contain a maximum
permitted number of user data octets. The number of user data
octets of the last SU which belongs to the set may have less
than the maximum length; unused octets are then padded with
dummy bits. 1Ae number of octets in the final SSU is encoded
in the "No. of octets in the final SSU" field of the ISU.
63 T channel transmission protocol
6.3.1.1 The T channel transmission protocol is used
when there are LSDUs present for transmission on the T
channel and the AES has received a requested T channel burst
reservation. The T channel transmission protocol specifies
reliable link service (RLS) for data transfer.
6.3.2 AIRCRAFETA RTH
STAT\ON (Am)
6.3.2.1 The aircraft earth station (AES) is the transmining
end of the T channel transmission protocol. The oldest
SU of the SUs with the highest Q number is transmitted first.
If an SU set is waiting for transmission in an allocated burst
reservation and a higher precedence SU set is submitted for
transmission then the higher precedence SUs will displace the
lower precedence SUs. Thus, a burst reservation may carry
SUs corresponding to an LSDU other than the one which
initiated the original request for reservation.
6.3.2.2 The AES, after transmitting the SU set to the
 
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