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as signalling to the transceiver external interface or implemented as a
short duration audible signal that is mixed with the received audio.
Free Running Voice Operation
While in TS3, the aircraft station shall process all V/D (voice) bursts without
regard to Group ID. Multiple V/D (voice) bursts with different Group ID shall
be processed on a first-come-first-serve basis, regardless of Group ID. Once a
particular V/D (voice) burst is processed, the aircraft station shall continue to
process only V/D (voice) bursts from the same user until EOM is indicated.
The aircraft station in TS3 timing state shall maintain system timing
autonomously. While in TS3, the aircraft station shall transmit V/D (voice)
bursts in the assigned time slot based on the system timing maintained by the
Note: Without beacons and ALT available to correct its time, an aircraft
station in TS3 is expected to drift relative to UTC at a rate determined by
the stability of its reference oscillator.
Link Management Support
When directed by the ground LME, the ground MAC sublayer shall transmit a
Poll Request message. An uplink beacon (see Table G-1)_shall be used to poll a
particular aircraft by including its Local ID. If an uplink beacon is not intended
to poll any user, the Aircraft ID field shall be set to zero. Whenever a beacon is
transmitted with the Aircraft ID field set to zero, the LBAC which would
otherwise be reserved for a Poll Response transmission becomes available for
random access (RA) transmissions (see Section 220.127.116.11.2.5.3). The aircraft MAC
sublayer shall deliver a received Poll Request message that is addressed to it to
the aircraft LME. Upon receiving a Poll Response from the aircraft LME, the
aircraft MAC sublayer shall stop the Reservation Request retransmission using
the random access M-channel until a new request is generated. The aircraft
radio shall respond to a poll by the ground station by transmitting a Reservation
Request message in LBAC 2, 3, or 4 for 3T configuration, and LBAC 1 for other
configurations in the MAC cycle immediately following the poll. This
opportunity to request a reservation shall be consistent with the procedures of
Section 18.104.22.168.22.214.171.124.3. The Number of Slots Requested field and the Voice
Request field shall be used independently for data access and voice request,
respectively. If the aircraft radio does not need to send data reservation or voice
request information, the Number of Slots Requested field and the Voice Request
field shall be set to zero.
The ground MAC sublayer shall deliver a received Poll Response message to the
ground LME. The ground station shall respond to a Reservation Request
message contained in a Poll Response using the procedures identified in Sections
126.96.36.199.188.8.131.52.1 and 184.108.40.206.220.127.116.11.3. Except during the net entry process (see
Section 18.104.22.168.2.1.2), no response shall be sent by the ground station if the
number of slots in the reservation field is zero and the Voice Request field is
encoded as “No Request”.
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