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时间:2010-07-20 23:51来源:蓝天飞行翻译 作者:admin
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without altering the facilities or shall send a CLEAR
CONFIRM ATION.
6.6.6.1 Supported facilities. Table 6-53 lists options and
facilities, documented in IS0 8208, that shall be supported by
VDL.
666.2 Unsupported facilities. Table 6-54 lists the
facilities, documented in IS0 8208, that shall not be supported
by the VDL.
6.6.6.3 Subnetwork establishment and connection
management. The subnetwork establishment and connection
management options used shall be chosen as required by the
operational conditions.
6.6.6.3.1 Subnetwork entity initialization. The ground
DCE shall be initialised on receipt of a valid XZD_CMD-LE.
The aircraft DCE shall be initialised on receipr of a valid
XID-RSP-LE.
Note.- Only the subnetwork entities corresponding to the
link on which the XIKCMD-LEiXID-RSP-L.E is received will
be initialized. The entities assigned to other links will not be
afsected.
6.6.6.3.2 Subnetwork connection establishment. Only
aircraft DTEs shall request subnetwork connection establishment
in the VDL subnetwork.
6.6.6.3.2.1 Explicit subnetwork connection establishment.
Immediately after link establishment, the aircraft DTE shall
attempt to establish a subnetwork connection to at least one
ground DTE. The aircraft DTE shall request a single subnetwork
connection per ground DTE by the transmission of a
CALL REQUEST packet specifying the ground DTE address
in the Called Address field. On receipt of the CALL
REQUEST, the ground DCE shall attempt to establish a subnetwork
connection to the specified DTE. A CALL CONFIRMATION
packet shall be sent to the aircraft DTE if the
connection is established; otherwise a CLEAR REQUEST
packet including a diagnostic specifying the cause of failure
shall be sent. The ground DCE shall use the Called Line
Address Modified Notification facility to inform the aircraft
DTE of the ground DTE's X.121 address.
Note.- The Calling Addressjeld in CLEAR CONFIRMATION
packet will contain the Aircraji DTE address.
6.6.6.3.2.2 Expedited subnetwork connection establishment.
An aircraft LME initiating expedited subnetwork
connection cstablishment shall implement this section. The
aircraft LME shall invoke the procedures described in
6.5.4.4.12 when connecting to a ground LME indicating
support for expedited subnetwork connection procedures. The
aircrafr DTE shall reissue CALL REQUESTS for those logical
channels for which responses (i.e. either a CALL CONFIRMATION
or a CLEAR REQUEST) were not included in the
XID-RSP-LE. The ground DCE shall use the Called Line
Address Modified Notification facility lo inform the aircraft
DTE of the ground DTE's X.121 address.
Note 1.- The CLEAR CONFIRMATION, if required, will
be transferred in an INFO frame.
Note 2.- The Calling Address Jield in CLEAR
CONFIRMATION packet will contain the Aircraji DTE
address.
6.6.6.3.3 Subnetwork connection maintenance. During
link establishment a ground DCE shall indicate its available
routers in the ATN Router NETS parameter and the aircraft
LME shall then attempt to maintain all subnetwork
connections.
Note.- For subnetwork connections to be maintained
across gmund station changes, the LME gives preference in
choosing n new ground station to ground stations indicating
accessibility to the DTEs to which subnetwork connections
already exist.
6,6.6.3.3. Explicit subnetwork connection muintenunce.
To explicitly request subnetwork connection mdntenance to a
ground DTE, an aircraft DTE shall send a CALL REQUEST
packet to the ground DTE with a fast select facility containing
a VDL mobile SNDCF Call User Data Field indicating a
request to maintain SNDCF context. If the ground DTE can
accept the call, it shall respond with a CALL ACCEPTED
packet with a fast select facility containing a VDL mobile
SNDCF Call User Data field indicating whether the SNDCF
context was maintained. If the DTE or a DCE is unable to
accept the call, it shall send a CLEAR REQUEST packet to
the aircraft DTE including a diagnostic specifying the cause of
failure. The ground DTE shall use the Called Line Address
Modified Notification facility to inform the aircraft DTE of
theground DTE's X. 121 address.
6.6.6.3.3.2 Expedited subnetwork connection
maintenance. An LME initiating expedited subnetwork
connection maintenance shall implement this section. If both
the aircraft and ground LMEs support expedited subnetwork
procedures, then the procedures described in 6.5.4.4.12 shall
be invoked. The initiating DTE shall reissue CALL
REQUESTS for those logical channels for which responses
 
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