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Annex 10 - Aeronautical Telecommunications Volume III
6.5.3.3.3.4 Address type. The address typc field is
described in Table 6-7.
6.5.3.3.3.5 Aircraft speciBc addresses. The aircraft
specific address field shall be the 24-bit ICAO aircraft address.
6.5.3.3.3.6 ICAO-administered ground station specific
addresses. The ICAO-administered ground station specific
address shall consist of a variable-length country code prefix
(using the same country code assignment defined in Annex 10,
Volume III, Chapter 9, Appendix 1, Table 1) and a suffix. The
appropriate authority shall assign the bits in the suffix.
6.5.3.3.3.7 ICAO-delegated ground station spec$c
addresses. The ICAO-delegated ground station specific
address shall be determined by the organization to which the
address space is delegated.
6.5.3.3.4 Broadcast address. The broadcast address shall
be used only as a destination address for unnumbered
information (UI) frames or for XID frames broadcasting
ground station information.
6.5.3.3.4.1 Encoding. The broadcast addresses shall be
encoded as in Table 6-8.
6.5.3.3.5 Link control field. The basic repedoire of
commands and responses for AVLC shall be as detailed in
Table 6-9 and shall be encoded as per IS0 4335.
6.5.3.3.6 Information field. The information field of an
SREJ shall be as dcfined in 6.5.3.11.2, an XTD shall be as
defined in 6.5.4.2, and all other frames shall be as defined in
IS0 4335.
6.5.3.4 DATA LINK SERVICE
SYSTEM PARAMETERS
These parameters needed by the DLS sub-layer shall be as
listed in Table 6-10 and detailed in 6.5.3.4.1 through 6.5.3.4.7.
DLS parameters shall be set using XlD frames.
6.5.3.4.1 Emer T1 (delay before retransmission). Timer
T1 shall be set to the time that a DLE will wait for an
acknowledgement before retransmitting an INFO, RR (P=l),
SREJ (P=l) or a FRMR frame.
The value of Timer TI shall be computed by the following
formula:
Timer T1 = Tlmin + 2TDgg + min(U(x),Tlmax)
TDg9 = (TMl*Ml)/(l-u) and is the running estimate for the
99th percentile transmission delay (between thc time at
which the frame is sent to the MAC sub-layer and the time
at which its transmission is completed);
u is a measurement of channel utilization with a range of
value from 0 to 1, with 1 corresponding to a channel that is
100 per cent occupied;
retrans is the largest retransmission count of all the
outstanding frames.
T1 shall be started after any INFO, RR (P=l), SREJ
@=I) or FRMR frame is queued for transmission unless it is
already running. If the timer expires, all outstanding INFO, RR
(P=l), SREJ (P=l) or FRMR frames that have been queued for
at least Tlmin + 2TD shall be retransmitted. The timer shall be
cancelled upon receipt of an acknowledgement.
After processing an acknowledgement or Timer T1 expires,
Zmer T1 shall be restarted if thee are still frames outstanding.
Whenever Timer T1 is restarted, the timer shall be set as if it
had been started when the oldest outstanding frame was
queued.
Note.- There is one rimer T1 per DLE.
6.5.3.4.2 Parameter T2 (delay before acknowledgement).
Parameter T2 defines the maximum time allowed for the DLE
to respond to any received frame (other than an XID) in order
to ensure the response is received before the peer DLE's Timer
T1 expires.
A station shall respond to any received frame (other than an
XID) within parameter T2 time in order to ensure the response
is received before the peer DLE's Timer T1 expires.
Note.- The period 72 should he a delay (shorter than the
Tlmin value of the peer DLE) to permit the acknowledging
DLE to schedule the response as an event in normal data
processing and to allow suficient time for an
acknowledgement while maximizing the likelihood that an
INFO frame will be tmmmijjed and eliminate the need for an
explicit acknowledgement.
6.5.3.4.3 Timer T3 (link initialization time). Timer T3
shall be set to the time that a DLE waits for an XID response
before retransmitting an exchange identification command
(mD-CMD). The period of Timer T3 shall be computed by
using the same algorithm and parameters of Timer T1, except
that T3min shall be separately negotiated. XTD-CMDs (except
for ground station information frames) shall be retransmitted
using the procedures dcfined in 6.5.3.4.1.
where:
Note 1.- There is one Zmer T3 per a DLE.
U(x) is a uniform random number generated between 0
and x; Note 2.- T3rnin shall be greater than Tlmin to allow the
responding entity t i m to co-ordinate the response andperfom
x = Tlmult* TD * ~ l e x p ~ ~ ~ ~ " ' any additional initialization processing.
 
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