This service can be used with any space data link

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Unformatted text preview: by the underlying Space Data Link Protocol to transfer Packets. CCSDS 130.2-G-1 Page 3-8 December 2007 CCSDS REPORT CONCERNING THE SPACE DATA LINK PROTOCOLS 3.3.4 3.3.4.1 SERVICES TO TRANSFER PRIVATE DATA General The Space Data Link Protocols provide services to transfer sequences of privately formatted SDUs (i.e., SDUs not formatted as Packets). 3.3.4.2 Services to Transfer Private Data Provided by TC-SDLP The TC-SDLP provides two services to transfer sequences of privately formatted SDUs: the MAP Access (MAPA) Service and the Virtual Channel Access (VCA) Service. The MAPA and VCA Services transfer sequences of privately formatted SDUs of variable length across a space link over a MAP Channel or a Virtual Channel, respectively. For the VCA Service, the length of the SDUs transferred by this service is constrained by the length of the Transfer Frames (see 4.1) used by the service provider. The MAPA Service includes a segmentation function, so the length constraint does not apply to SDUs transferred by the MAPA Service. Both Sequence-Controlled (Type-A) and Expedited (Type-B) service types (see 3.2.2.2) are provided for these services. The sending user specifies for each SDU whether Type-A or Type-B should be applied. In a Virtual Channel that provides the VCA Service, only one user can use this service, and SDUs from different users are not multiplexed together within the Virtual Channel. In a MAP Channel that provides the MAPA Service, only one user can use this service, and SDUs from different users are not multiplexed together within the MAP Channel. 3.3.4.3 Services to Transfer Private Data Provided by TM-SDLP and AOS-SDLP The TM-SDLP and AOS-SDLP each provide a VCA Service that transfers a sequence of privately formatted SDUs of fixed length over a Virtual Channel across a space link. The length of the SDUs transferred by this service is determined by the length of the Transfer Frames (see 4.1) used by the service provider. The VCA Service is either asynchronous (see 3.2.4.3.2) or periodic (see 3.2.4.3.4). The service does not guarantee completeness, but it may signal gaps in the sequence of SDUs delivered to the receiving user. In a Virtual Channel that provides the VCA Service, only one user can use this service, and SDUs from different users are not multiplexed together within the Virtual Channel. CCSDS 130.2-G-1 Page 3-9 December 2007 CCSDS REPORT CONCERNING THE SPACE DATA LINK PROTOCOLS 3.3.5 3.3.5.1 SERVICES TO TRANSFER SHORT, FIXED-LENGTH DATA General The TM-SDLP and AOS-SDLP provide services to transfer sequences of short, fixed-length SDUs. These services are used to transfer, at relatively short intervals, data used for spacecraft operations (for example, reports on command reception or data used for clock calibration). These services are synchronous (see 3.2.4.3.3). 3.3.5.2 Services to Transfer Short, Fixed-Length Data Provided by TM-SDLP The TM-SDLP provides four services to transfer sequences of short, fixed-length SDUs: the Virtual Channel Frame Secondary Header (VC_FSH) Service, the Virtual Channel Operational Control Field (VC_OCF) Service, the Master Channel Frame Secondary Header (MC_FSH) Service and the Master Channel Operational Control Field (MC_OCF) Service. The VC_FSH and VC_OCF Services provide transfer of fixed-length SDUs synchronized with the release of Transfer...
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This document was uploaded on 03/06/2014.

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