Note the vca status fields parameter consists of the

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Unformatted text preview: e First Header Pointer Field and three other bits of the Transfer Frame Status Field: the Packet Order Flag (1 bit), and Segment Length ID (2 bits). These are undefined by CCSDS when a Virtual Channel is used to transfer VCA_SDUs. 3.4.2.4 GVCID The GVCID parameter shall contain a GVCID that indicates the Virtual Channel through which the VCA_SDU is to be transferred. NOTE – The GVCID parameter is the SAP address of the VCA Service. 3.4.2.5 VCA_SDU Loss Flag The VCA_SDU Loss Flag is an optional parameter that may be used to notify the user at the receiving end of the VCA Service that a sequence discontinuity has been detected and that one or more VCA_SDUs have been lost. If implemented, the flag shall be derived by examining the Virtual Channel Frame Count in the Transfer Frames. CCSDS 132.0-B-1 Page 3-7 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL 3.4.3 VCA SERVICE PRIMITIVES 3.4.3.1 General The service primitives associated with the VCA Service are: a) VCA.request; b) VCA.indication. 3.4.3.2 VCA.request 3.4.3.2.1 Function At the sending end, the VCA Service user shall pass a VCA.request primitive to the service provider to request that a VCA_SDU be transferred to the user at the receiving end through the specified Virtual Channel. NOTE – The VCA.request primitive shall be the service request primitive for the VCA Service. 3.4.3.2.2 Semantics The VCA.request primitive shall provide parameters as follows: VCA.request 3.4.3.2.3 (VCA_SDU, VCA Status Fields, GVCID) When Generated The VCA.request primitive shall be passed to the service provider to request it to send the VCA_SDU. 3.4.3.2.4 Effect On Receipt Receipt of the VCA.request primitive shall cause the service provider to transfer the VCA_SDU. 3.4.3.2.5 Additional Comments The VCA.request primitive shall be used to transfer VCA_SDUs across the space link on the specified Virtual Channel. CCSDS 132.0-B-1 Page 3-8 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL 3.4.3.3 VCA.indication 3.4.3.3.1 Function At the sending end, the service provider shall pas...
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