At the receiving end of the tc system management

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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 Reference [2]. 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 Reference [2]. 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 PEER PROCESS SENDING END RECEIVING END SYSTEM MANAGEMENT LAYER INPUT: NAMED SETS OF APPLICATION DATA. TRANSPORT CONTROL PARAMETERS. FUNCTION: ENCAPSULATE 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 SERVICE TRANSPORT–TC APPLICATION DATA FUNCTION: EXTRACT AND RECONSTRUCT NAMED SETS OF APPLICATION DATA IN SEQUENTIAL ORDER. FORMULATE TRANSPORT STATUS REPORTS. TELECOMMAND PACKETS OUTPUT: TC PACKETS. TC FILES. ROUTING...
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