Ccsds 1320 b 1 page 4 4 september 2003 ccsds

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Unformatted text preview: Transfer Frame transmitted within a specific Virtual Channel. 4.1.2.6.3 A re-setting of the Virtual Channel Frame Count before reaching 255 shall not take place unless it is unavoidable. NOTE – The purpose of this field is to provide individual accountability for each Virtual Channel, primarily to enable systematic Packet extraction from the Transfer Frame Data Field. If the Virtual Channel Frame Count is re-set because of an unavoidable re-initialization, the completeness of a sequence of Transfer Frames in the related Virtual Channel cannot be determined. 4.1.2.7 Transfer Frame Data Field Status 4.1.2.7.1 General 4.1.2.7.1.1 Bits 32–47 of the Transfer Frame Primary Header shall contain the Transfer Frame Data Field Status. 4.1.2.7.1.2 This 16-bit field shall be sub-divided into five sub-fields, as follows: a) Transfer Frame Secondary Header Flag (1 bit, mandatory); b) Synchronization Flag (1 bit, mandatory); c) Packet Order Flag (1 bit, mandatory); d) Segment Length Identifier (2 bits, mandatory); e) First Header Pointer (11 bits, mandatory). NOTE – The format of the Transfer Frame Data Field Status is shown in figure 4-3. CCSDS 132.0-B-1 Page 4-5 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL TRANSFER FRAME DATA FIELD STATUS (2 octets) TRANSFER FRAME SECONDARY HEADER FLAG SYNCH. FLAG PACKET ORDER FLAG 1 bit 1 bit SEGMENT LENGTH ID 1 bit 2 bits FIRST HEADER POINTER 11 bits Figure 4-3: Transfer Frame Data Field Status 4.1.2.7.2 Transfer Frame Secondary Header Flag 4.1.2.7.2.1 Bit 32 of the Transfer Frame Primary Header shall contain the Transfer Frame Secondary Header Flag. 4.1.2.7.2.2 The Transfer Frame Secondary Header Flag shall signal the presence or absence of the Transfer Frame Secondary Header. It shall be ‘1’ if a Transfer Frame Secondary Header is present; it shall be ‘0’ if a Transfer Frame Secondary Header is not present. 4.1.2.7.2.3 The Transfer Frame Secondary Header Flag shall be static within the associated Master or Virtual Channel throughout a Mission Phase. NOTE – For the significance of the above-mentioned as...
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