In this case only the two least significant bits are

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Unformatted text preview: of a Transfer Frame with N(S) = V(R), receipt of a ‘Set V(R)’ Control Command (unless in ‘Lockout’ State) or receipt of an ‘Unlock’ Control Command. 6.1.6 FARM-B_COUNTER This variable is incremented whenever a valid Type-BD or Type-BC Transfer Frame arrives. The value of this variable is inserted into the CLCW, but is not used by the COP-1 state machines at either end of the link. The counter is intended for use by layers above the Data CCSDS 232.1-B-2 Page 6-2 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 Link Layer to offer a minimal facility for a higher layer error-control loop when the Expedited Service (BD Service) is used. NOTES 1 How the higher layers at the sending end access the CLCW to obtain the value of the FARM-B_Counter is not defined in this Recommended Standard. It is implementation-dependent. 2 Some implementations may choose to maintain a FARM-B_Counter with more than two bits. In this case, only the two least significant bits are placed in the CLCW. The full counter may be communicated to the sending end by other means. 6.1.7 RECEIVER_FRAME_SEQUENCE_NUMBER V(R) This variable records the value of N(S) expected to be seen in the next Type-AD Transfer Frame on this Virtual Channel. 6.1.8 FARM SLIDING WINDOW VARIABLES Purpose The purpose of the COP-1 Sliding Windows is to protect FARM-1 against the unauthorized (uncontrolled) transfer of a sequence of Transfer Frames such that the Frame Sequence Number, N(S), of one or more of these Transfer Frames will exceed the current value of the Receiver_Frame_Sequence_Number, V(R), by at least 256. The purpose of the FOP Sliding Window (defined in terms of its width, ‘K’, in 5.1.12, ‘FOP_Sliding_Window_Width (K)’) is to limit the number of Transfer Frames which can be transmitted safely ahead of the last acknowledged Transfer Frame. The purpose of the FARM Sliding Window is to protect FARM-1 against any malfunction or erroneous setup of FOP-1. The FARM Sliding Window is defined in terms of three variables: a) its total width, referred to as ‘W’; b) the width of its positive part, referred to a...
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