2 for the pvns presently authorized by ccsds see

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Unformatted text preview: horized by CCSDS, see reference [4]. 3.2.3 VIRTUAL CHANNEL ACCESS SERVICE DATA UNIT (VCA_SDU) VCA_SDUs shall be transferred over a space link with the Virtual Channel Access Service. NOTE – Virtual Channel Access Service Data Units (VCA_SDUs) are fixed-length, octetaligned data units, the format of which is unknown to the service provider. Their length is established by management. 3.2.4 FRAME SECONDARY HEADER SERVICE DATA UNIT (FSH_SDU) 3.2.4.1 Frame Secondary Header Service Data Units (FSH_SDUs) shall be transferred over a space link with the VC_FSH or MC_FSH Service. Data units may be carried in every frame of a Virtual Channel, using the VC_FSH Service, or, in every frame of a Master Channel, using the MC_FSH Service. 3.2.4.2 Although the transfer of FSH_SDUs is synchronized with the Virtual Channel or Master Channel that will provide the transfer service, the creation of FSH_SDUs by the sending user may or may not be synchronized with the Virtual Channel or Master Channel. Such synchronization, if required for timing or other purposes, is a mission-design issue. NOTE – Frame Secondary Header Service Data Units (FSH_SDUs) are fixed-length data units carried in the Transfer Frame Secondary Header (FSH), defined in 4.1.3, from a sending end to a receiving end. Their length may be of any constant value which is an integral number of octets, between 2 octets and 64 octets. It shall be static within the associated Master or Virtual Channel, and is established by management. Except for the Frame Secondary Header Identification Field defined in 4.1.3.2, CCSDS specifies no format or semantics for the content of an FSH_SDU. 3.2.5 OPERATIONAL CONTROL FIELD SERVICE DATA UNIT (OCF_SDU) 3.2.5.1 Operational Control Field Service Data Units (OCF_SDUs) shall be transferred over a space link with the VC_OCF or MC_OCF Service. Data units may be carried in every frame of a Virtual Channel, using the VC_OCF Service, or, in every frame of a Master Channel, using the MC_OCF Service. 3.2.5.2 Although the tran...
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