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3. See Section 220.127.116.11.4.1.5 for additional rules limiting transition from TS0 to
other timing states.
The net entry procedure shall begin with the aircraft station transmitting a Net
Entry Request message following the successful net initialization. The
transmission of the Net Entry Request message and the subsequent
retransmission, if enabled, shall follow the procedures described in Appendix I.
The Net Entry retransmission shall continue until a Net Entry Response message
is received. If a Net Entry Response message is received, the aircraft station shall
transmit a Poll Response message in the next MAC cycle. If the Net Entry
Response message is of type "previous link preserved," the aircraft TL3 timer
(Table 3-66a) shall be stopped.
Note 1: All configurations that offer one or more data circuit(s) must support
net entry (3V1D, 2V2D, 2V1D, 1V3D, 1V2D, 3T). The voice only
configurations (3V, 4V, 3S, and 2S1X) may support net entry if discrete
addressing is enabled by the ground user.
In cases where multiple aircraft radios are installed on a single aircraft, the
transmission of the Net Entry Request message and the initial Poll Response
message from each radio shall be delayed by a different number of symbol
Note 2: This requirement is to prevent multiple messages in the same time slot
from adding constructively, creating a situation where multiple radios
have the same Local ID. A convenient way to implement this
requirement would be to delay these particular down link transmissions
by an amount equal to (SDI-1) symbol periods. The Source/Destination
Indicator (SDI) is discussed in Appendix H.
Upon receiving a Net Entry Request message, the ground shall assign the next
available Local User ID to the requesting aircraft. The ground station shall check
to see if the aircraft ICAO address already has an active Local ID association
within the same User Group since it was assigned. If so, the ground shall
transmit the Net Entry Response message of type “previous link preserved.” If
not, the pending disconnect link table shall be examined. If the aircraft ICAO
address is found in the table, the link status shall be reinstated, the TL3 timer
shall be stopped, and the link port address shall be changed to the new radio
station port address. The ground shall transmit the Net Entry Response message
of type "previous link preserved."
If a ground station receives a duplicate Net Entry Request (i.e., from the same
ICAO Address) prior to transmitting a Net Entry Response to the initial pending
request, the duplicate shall be ignored.
If the aircraft ICAO address is not found in the table and a Local ID has been
assigned, the ground shall transmit a Net Entry Response message of type "no
previous link." When the Poll Response message is received by the ground
station, the ground station shall respond by sending a Reservation Response,
contained within a Supported Options message, to the entering aircraft during the
next MAC cycle. This response shall be either a reservation or a RACK if data
slots were requested or a "no reservation" indication if no data slots were
requested. If an aircraft receives a Net Entry Response message of type "no
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