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Unformatted text preview: on data may (if required by the application processes) be translated back into
correspondingly named sets of command directives, or may be passed directly to the layer
above. Status reports may be formulated and returned to the sending end of the layer (via
Telemetry Packets) if information relating to the correctness, completeness, and sequentiality of
the received data is required by particular mission processes: the CCSDS presently does not
define these reports.
Session control instructions are created by the sending end of the System Management layer,
which are addressed to the receiving end of the layer and are passed to the layer below for
transport. These session control instructions to the receiving end of the layer define naming
conventions and conditions for delivering either the application data or the retranslated
command directives to the TC Application Process layer. 3 . 1 . 3 TC PACKETIZATION LAYER
The TC Packetization layer is currently the highest layer which CCSDS Recommendations
cover in detail. The TC Packet is an autonomous command data unit which may be directly
interpreted by the device that is being controlled. The format of the TC Packet is specified in
The basic service of the TC Packetization layer is to provide error-free transport of one set of
application data to the System Management layer on the spacecraft. An enhanced service is to
provide error-free transport of the application data content of named sets of interdependent TC
Packets (i.e., TC Files) to the TC System Management layer on the spacecraft. Figure 3-3
depicts the activities and interfaces of the TC Packetization layer.
Inputs to the sending end of the Packetization layer are named sets of transportable TC
application data, plus transport control instructions including naming conventions. The TC
application data are placed within the data field of TC Packets, and encapsulated within Packet
headers containing information such as the name of destination application, sequence control,
and packet length. If required, TC Files are constructed according to the procedures defined in
The TC Packets, or files of TC Packets, are passed to the layer below along with control
instructions that request lower layer services such as the segmentation or multiplexing of
packets or files. TC Packets may also be created for routing to the receiving end of the
Issue 6 Page 3-4 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE PACKETIZATION LAYER
END SYSTEM MANAGEMENT LAYER INPUT: NAMED SETS OF APPLICATION DATA. TRANSPORT
APPLICATION DATA INTO
TC PACKETS OR FILES
OF TC PACKETS.
REQUEST DATA ROUTING
SERVICE (E.G., MULTIPLEXER
ACCESS POINTS). OUTPUT: NAMED SETS OF
APPLICATION DATA. END-TO-END
DATA FUNCTION: EXTRACT AND
RECONSTRUCT NAMED SETS
OF APPLICATION DATA IN
STATUS REPORTS. TELECOMMAND
OUTPUT: TC PACKETS.
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This document was uploaded on 03/06/2014.
- Spring '14