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the idle to busy detection than the busy to idle detection
because of the effects of the two diferent errors.
* All figures are located at the end of this chapter.
Annex 10 - Aeronautical TelecommunZcations Volume I11
6.4.3.3 RECEIVERITRANSMITTER
INTERACTION
6.4.3.3.1 Receiver to trartsmitter turnaround time. A
station shall begin the transmission of the unique word portion
of the training sequence within 1 millisecond after terminating
the receiver function. The total frequency change during the
transmission of the unique word shall be less than 10 Hz. After
transmission of the unique word, the phase acceleration shall
be less than 500 Hz per second.
6.4.3.3.2 Trammitter to receiver turnaround time. The
transmitted power level shall decay at least by 20 dB within
0.3 milliseconds after completing a transmission. A station
shall be capable of receiving and demodulating with nominal
performance, an incoming signal within 1.5 milliseconds after
transmission of the final information symbol.
6.5.1.2.2 Connection-less. The VDL link layer shall
provide an unacknowledged broadcast service using a
connection-less DLS sub-layer.
6.5.2 MAC sub-layer
6.5.2.1 The MAC sub-layer shall provide for the
transparent acquisition of the shared communications path. It
makes invisible to the DLS sub-layer the way in which
supporting communications resources are utilized to achieve
this.
Note.- The service specijication for the MAC sub-layer is
modeled on the MAC Service Definition ( I S 0 DP 10039).
6.5.2.2 MAC SERVICES
6.4.4 Physical layer system
parameters 6.5.2.2.1 Multiple access. The MAC sub-layer shall
implement a non-adaptive p-persistent CSMA algorithm to
6.4.4.1 The physical layer shall implement the system equitably allow all stations the opportunity to transmit while
parameters as defined in Table 6-5. maximizing system throughput, minimizing transit delays, and
minimizing collisions.
6.4.4.1.1 Parameter PI (minimum transmission length).
Parameter PI defines the minimum transmission length that a 6.5.2.2.2 Channel congestion. The MAC sub-layer shall
notify the VME sub-layer whenever channel congestion is
receiver shall be capable of demodulating without degradation
of BER. detected (see 6.5.2.3.2).
6.5 LINK LAYER PROTOCOLS
AND SERVICES
6.5.1 General information
6.5.2.3 MAC service system parameters. The MAC
service shall implement the system parameters defined in
Table 6-6.
6.5.2.3.1 Emer TMI (inter-access delay timer). Timer
TM1 shall be set to the time (TMl) that a MAC sub-layer will
wait between attemuts to access the channel. This timer shall
be started if it is nit already running and the channel is idle
5 Functionaliq The VHF digital link (WL) link after an unsuccessful access atrempts ne timer shall be
layer shall provide the following sub-layer functions: cancelled if the channel becomes busy. When the timer expires
a) media access control (MAC) sub-layer, which requires
another access attempt shall be made.
the use of the carrier sense multiple access (c&)
algorithm; 6.5.2.3.2 Timer TM2 (channel busy timer). Timer TM2
shall be set lo the maximum time (TM2) that a MAC sub-layer
will wait after receiving a request to transmit. Th~tsim er shall
b) rl data link service @LS) sub-layer, providing
connection-oriented point-to-point links using data link be started if it is not already running, when the MAC sub-layer
receives a request for transmission. The timer shall be
entities (DLE) and connection-less broadcast link over cancelled upon a successful access attempt. When the timer
the MAC sub-layer; and expires, the VME shall be informed that the channel is
congested.
C) a VDL management entity (VME), which establishes
and maintains DLEs between the aircraft and the 6.5.2.3.3 Parameter p (persistence J. Parameter p (0 < p ground-based systems using link management entities
(LME).
-< 1) shall be the probability that the MAC sub-layer will
transmit on any access attempt. An access attempt shall be a
Bernoulli process with a probability of success equal to p.
6.5.1.2 SERVICE
6.5.2.3.4 Counter MI (maximum number of access
6.5.1.2.1 Connection-oriented. The VDL link layer shall attempts). Counter M1 shall be set to the maximum number of
providc a reliable point-to-point service using a attempts (MI) that a MAC sub-layer will make for my
connection-oriented DLS sub-layex. transmission request. This counler shall be cleared upon:
Part 1 Annex 10 - Aeronautical Telecommunications
system initialization, Timer TM2 expiring, or a successful Note.- Unique sorrrce und destination addresses are
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