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时间:2010-07-21 23:04来源:蓝天飞行翻译 作者:admin
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shall request a modification of an existing link connection's
parameters by sending an XID-CMD-LPM (P=l) to the
aircraft LME containing the parametcrs as per Table 6-51.
6.5.4.4.5.2 General aircrafi response. The aircraft LhE
shall acknowledge with an XXDRSP-LPM containing the
parameters as per Table 6-5 1.
6.5.4.4.5.3 Recommendation.- If Counter N2 is
exceeded for the XID-CMD-LPM, the ground LME should
6.5.4.4.4.1 Aircrafr initiation. The aircraft LME shall attempt ti handojfvia another station before disconnecting the
choosc a -gr ound station with which it wishes to establish a link link to the aircrafl.
based on the signal quality of all received uplink frames and
on information in any received GSIFs. It shall then attempt to 6.5.4.4.6 Aircrafr-initiated hand08 If an aircraft LME
establish a Link with the chosen ground station by sending an implements this section, then it shall set the "i" bit in the
XID-CMRLE (P=l) frame. This frame shall include the AVLC Specific Options parameter to 1; otherwise, it shall set
mandatory parameters as per Table 6-51 and also any optional the "i" bit to 0.
parametersfor which the-aircraft LME does not wish-to use
the default value. K the aircraft LME has received a GSIF from 6.5.4.4.6.1 Aircrafr hand08 Once the aircraft LME has
the ground station to which it is transmitting the established a link to a ground station, it shall monitor the VHF
XID-CMD-LE (P=l), then it shall use the parameters as signal quality on the link and the transmissions of the other
declared; otherwise, it shall use the default parameters. ground stations. The aircraft LME shall establish a link to a
new ground station if any of the following events occur:
6-5.4.4.4.2 General ground response. If the ground LME
receives the XID-CMD-LE, it shall confirm link
establishrnent by sending an XD-RSP-LE frame containing
the parameters as per Table 6-51. The ground LME shall
include in the XII-RSPLE any optional parameters for
which it is not using the default values. If the XIDRSP-LE
includes Ihe Autotune parameter then the Replacement Ground
Station List parameter shall be included indicating the ground
stations on the new frequency that the aircraft LME can
establi.sh a new link using the operating parameters specified
in the XID-RSPLE. If the XID-RSP-LE does not include the
Autotune parameter, the ground LME shall include the
R~placement Ground Station List parameter if it wishes to
indicale the ground stations which can be reached on the
current frequency using the same operating parameters as the
transmitting station.
6.5.4.4.4.3 Excc.ptionrz1 cases. If an LME receiving the
XID-CMD-LE cannot establish the link with the sending
LME, then it shall transmit an XID-RSP-LCR (F=l) instead
of an XID-RSP-LE (F=l). If the parameters in the
XID-RSP-LE from the ground LME are not acceplable to the
aircraft LME, then the aircraft LME shall transmit a DISC to
the ground. If the Autotune parameter is included in the
XU3-RSP-LE and the aircraft LME is unable to perform the
autotune, then the aircraft LME shall respond with an
m-CMD-L.CR (P=O); the link established on the current
frcquency shall not be affected, While waiting for a response
to an XD-CMDLE, an aircraft LME receiving any unicasted
frame other than a TEST or an XU3 shall retransmit the
XID-CMD-LE instead uf transmitting a DM.
Note.- See 6.5.3.8 on the processing of an XID-CMD.
a) the VHF signal quality on the current link is poor and
the signal quality of another ground station is
significantly better;
b) Counter N2 is exceeded on any frame sent to the current
ground station;
c) Timer TG2 expires for the current link, or
d) Timer 'lM2 expircs. In this case, the aircraft LME shall
autonomously tune to an alternate frequency (provided
in a frequency supporl list) before illitiating the halldo&
6.5.4.4.6.2 Site selection preference. From among those
ground stalions with acceptable link quality, the aircraft LME
shall prefer to handoff to a ground station which indicates (in
the GSIF) accessibility to the air-ground router(s) to which the
aircraft DTE has subnetwork connections.
6.5.4.4.6.3 Recommendation.- If arz aircrafl has
conzrnenced approacii to its destination airport and its current
link is with a ground station tlzar does not ofSer service at that
airport, it should hadoff to a ground starion which indicates
in its Airport Coverage Indicarion parameter tf~arit offers
service at that airport.
6.5.4.4.6.4 lntemction of LMEs. When an aircraft VME
hands off from a ground station in one ground-based systcm
(and thus associated with one LME) to a ground station in
 
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