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时间:2010-07-21 23:04来源:蓝天飞行翻译 作者:admin
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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 pmtocol specifies reliable link
service (RLS) for data transfer.
6.3.2 AIRCFL4FT EARTH
STATION (AES)
6.3.2.1 The aircraft earth station (AES) is the transmitting
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
ground earth station (GES), waits for T channel
acknowledgement (TACK) SU(s) from the GES. The TACK
SUs are received at the AES by the receiving end of the P
channel protocol, which then passes them to the T channel
transmission protocol. The AES may receive more than one
TACK SU indicating the missing SUs of an SU set at the GES.
Each TACK SU can identify up to three missing SUs. The
receipt of a TACK SU of the TACK SU set identifying the
missing SUs, initiates a timer tA5 in the AES and indicates the
number of additional TACK SUs that are expected. If the timer
tA5 expires before another TACK SU of the TACK SU set is
received, the AES transmits the missing SUs identified in the
so far received TACK SUs. If TACK SU(s) are received after
the corresponding timer tA5 has expired and the AES has not
yet transmitted the retransmission SU set identified in the
received TACK SU(s), the AES discards the received TACK
SU(s).
6.3.2.5 If &r several retries, an expecred reservatjon
from the GES is not received, the AES discards at least the
number of SUs for which the reservation was requested. The
SUs discarded may not be those which initiated the original
request for reservation because of the fact that the transmission
of SUs is based upon the precedence described in Annex 10,
Volume III, Part I, Chapter 4, 4.6.4.2.2, but will be of equal or
lower precedence. If an ISU is among the SUs discarded at the
AES, the complete SU set headed by the discarded ISU is
discarded. This may result in discarding more SUs than
required. If the SU discarded is a REQ SU, then the AES
retransmits the REQ SU on either the T or R channel. If the
SU discarded is a last SU of an SU set, then the AES starts a
timer for the supervision of TACK SU(s) for that SU set.
6.3.3 GROUNDEA RTH
STATION (GES)
6.3.3.1 This is the receiving end of the T channel
transmission protocol. The GES, upon receipt of an SU set,
reassembles it into an LSDU. Before reassembling the SU set.
the GES checks whether or not all the SUs of the SU set have
been received. If the SU set is not complete after no more SUs
of the SU set are expected (determined by the criterion
specified in the AMSS SAWS), the GES requests for the
retransmission of the missing SUs by transmitting appropriate
number of TACK SUs, indicating error, on the P channel to the
a s .
6.3.3.2 If while waiting for retransmissions from the AES,
the GES receives an ISU with the same AES ID and Q number
as the SU set awaiting completion and with a reference
number belonging to a pair whose other member is the
reference number of the SU set awaiting completion, the GES
discards the SU set awaiting completion and proceeds with the
new SU set. The receipt of the ISU with the parameters
described above indicates that the AES has given up on the
transmission of the previous SU set and has released the
reference number, thus making available the other member of
the pair for assignment.
6.3.2.3 The AES computes the length of the expected 6.3.3.3 The GES may receive an RQA SU from the AES
reservation for retransmission based upon the number of in the following circumstances:
missing SUs indicated in the received TACK SUs of the TACK
SU set. This length is associated with the timer tA8 initiated a) initial SU set loss (i.e. loss of at least the ISU): the RQA
by the T channel reservation protocol to supervise the receipt SU does not refer to an SU set which has been processed
of reservation for retransmission. This length may be less than just before;
-24 UOO No. 75
Annex 10 - Aeronautical TelecommunLa#o~s volume 112
b) negative acknowledgement loss or retransmission loss:
the RQA SU refers to an SU set under correction; and
 
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