4232 a virtual channel frame count shall be generated

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Unformatted text preview: TM SPACE DATA LINK PROTOCOL 4.2.3.3 If there is a user of the VC_FSH Service for a particular Virtual Channel, an FSH_SDU supplied by the user shall be placed in the Transfer Frame Secondary Header. If there is a user of the VC_OCF Service for a particular Virtual Channel, an OCF_SDU supplied by the user shall be placed in the Operational Control Field. The Master Channel Frame Count field of Transfer Frames shall be kept empty by the Virtual Channel Generation Function. The following fields of Transfer Frames, if present for the particular Physical or Master Channel, shall also be kept empty by the Virtual Channel Generation Function: a) MC_FSH; b) MC_OCF; and c) Frame Error Control Field. 4.2.3.4 An abstract model of the Virtual Channel Generation Function is illustrated in figure 4-7. Only one of these two entities exists for a Virtual Channel Packet Proc. Function Transfer Frame Data Fields Virtual Channel Generation Function for a Virtual Channel VCA Service User VCA_SDUs VC_FSH Service User VC_OCF Service User FSH_SDUs OCF_SDUs Transfer Frame Generation VC Frames Virtual Channel Multiplexing Function Figure 4-7: Abstract Model of Virtual Channel Generation Function 4.2.4 VIRTUAL CHANNEL MULTIPLEXING FUNCTION 4.2.4.1 The Virtual Channel Multiplexing Function shall be used to multiplex Transfer Frames of different Virtual Channels of a Master Channel. NOTE – There is an instance of the Virtual Channel Multiplexing Function for each Master Channel that has multiple Virtual Channels. 4.2.4.2 The Virtual Channel Multiplexing Function shall multiplex Transfer Frames received from the instances of the Virtual Channel Generation Function and, if present, the CCSDS 132.0-B-1 Page 4-17 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL Virtual Channel Frame Service users, and shall put them into a queue of Transfer Frames in an appropriate order that is set by management. 4.2.4.3 The algorithm used to order the Transfer Frames is not specified by CCSDS, but shall be defined by project organizations, considering factors such as priority, release rate, isochronous timing requirements, etc...
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This document was uploaded on 03/06/2014.

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