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assigned ta the AES at the time of log*, is implementation
dependent. The follmmg methods may be utilized for
selecting the T channel:
a) all T channels available to a particular AES are polled.
Reservations are assigned to any T channel on which the
minimum allowable reservation delay is achievable, or
to the channel offering the shorkst reservation delay if
no T channel offers the minimum allowable reservation
delay;
No. 75
Allachment A lo Part I Annex 10 - Aeronituricul TelecommunicuHons
b) each T channel assigned to a particular AES is latter case, the GES will delay T channel burst assignment
associated with one or more message precedence. A until capacity is available. The length of the reservation for
T channel is selected according to the precedence of the reuansrnission is the number of missing SUs identified by the
message identified in the REQ SU; and TACK SU set indicating missing SUs at the GES plus one.
c) reservations for all non-safety messages are made on a
single T channel; reservations for all safety messages are
made on a T channel which offers a shortest reservation
delay.
6.4.3.3 The GES transmits the RES SU to the AES
whenever the start of the reservation is within eight seconds of
the current time. This is done to avoid any misinterpretation of
the reservation start time at the AES. The reservation start time
in the RES SU is specified in terms of start frame number
within a superftame. The superframe number is not specified.
So, if the RES SU is not received by the AES within the
superframe which actually includes the start frame number, the
AES will apply the information incorrectly to the superframe
within which the RES SU is received by the AES. If the
frames in this superframe have been assigned to another AES,
then there could be a collision of the T channel transmissions
from the two AESs. Because of the fact that the RES SU
should be received by the AES within the correct superframe,
the precedence of the RES SU is set to 15 in order to minimize
the P channel queuing delays that otherwise can be
experienced by the RES SU.
6.4.3.4 If the start of the burst reservation is outside the
eight second time window from the time the reservation was
made, the GES transmits a reservation forthcoming (TZFC) SU
to the AES in order to prevent a timeout resulting in another
request for reservation. The RFC SU gives an upper limit for
the delay to the start of burst reservation in entire number of
super frames (8 seconds). The time-plan in the GES is limited
in length. Whenever the GES is not capable to assign a
reservation within its current time-plan, it sends an WC SU
with the delay to RES set equal to its maximum time-plan
length and saves the request for later assignment.
Subsequently, when the GES is capable of serving the request,
the GES sends a further RFC SU giving the delay to
reservation which is now known. The size of the GES timeplan
is implementation dependent and has not been specified
in the AMSS SAWS.
6.4.3.5 The TACK SUs transmission must always precede
the associated T channel reservation. As the precedence level
of an RES SU is higher than the one of the TACK SU. the GES
must wait until all TACK SUs have been effectively
transmitted before allocating a reservation for retransmission.
The TACK $Us transmitted to the AES by the T channel
transmission protocol in the GES includes an estimation for
the delay before the RES SU will be sent to the AES by the
GES; this estimation is a function of the T channel(s) loading.
Subsequently, if the reservation cannot be assigned within the
estimated delay specified in the TACK SU, the GES transmits
an RFC SU with the actual delay or with the maximum delay
value corresponding to its time-plan length if it has not been
able to assign a reservation within its current time-plan. In the
6.4.3.6 The GES assigns reservations such that no two
AESs use the same T channel for transmission at the same
time. The length of a reservation is such that the AES is
always capable to send at least one REQ SU in addition to the
SUs for which the reservation is made. This prevents delaying
either the transmission of an REQ SU when its precedence
level is lower than the precedence level of the SUs awaiting
transmission, or the transmission of the complete SU set when
intempted by a single REQ SU. Long LSDUs are assigned
burst reservation in multiple bursts of equal length, each burst
being separated from the precedent one by a fixed burst
internal. The intervals between bursts can be assigned to AESs
for transmission or retransmissions. The burst interval between
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