These considerations mean that it must be possible to

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Unformatted text preview: The state machine is in the ‘Initial’ State (S6) whenever it is necessary to terminate an ongoing service (this happens when a ‘Terminate AD Service’ Directive is received or when an ‘exception’, i.e., an event that causes an ‘Alert’, occurs). In principle, the ‘Initial’ State is the first state entered by the state machine for a particular Virtual Channel. While in principle all of these Virtual Channels remain open during the life of the mission, provisions must be made for interruptions of the communications link between the sending and receiving ends and for the operation of multiple senders for the same receiving end. These considerations mean that it must be possible to start up a state machine at a sending end more CCSDS 232.1-B-2 Page 5-2 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 than once during the life of the mission. State S6 shall also be used when the AD Service is suspended. In the ‘Initial’ State, FDUs may only be transmitted if they are Type-BD Transfer Frames. To start the Sequence-Controlled Service, it is necessary to execute one of the four possible ‘Initiate AD Service’ Directives. If the Directive is accepted and successfully executed, the state machine will be set to the ‘Active’ State (S1). If the Directive is not successfully executed (as would be the case if the transmission of an ‘Unlock’ BC Transfer Frame were not confirmed in the CLCW reports from the receiving end after the maximum allowed number of timer-initiated retransmissions), FOP-1 shall generate an ‘Alert’ notification and reenter the ‘Initial’ State. 5.1.3 TRANSMITTER_FRAME_SEQUENCE_NUMBER, V(S) The Transmitter_Frame_Sequence_Number, V(S), contains the value of the Frame Sequence Number, N(S), to be put in the Transfer Frame Primary Header of the next Type-AD Transfer Frame to be transmitted. 5.1.4 WAIT_QUEUE When Type-AD FDUs are received from the Higher Procedures, they shall be held in the Wait_Queue until they can be accepted by FOP-1. The Wait_Queue has a maximum capacity of one FDU. The Wait_Queue and ‘Accept Response to Request to Transfer FDU’ form the primary mechanism by which flow control as seen b...
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This document was uploaded on 03/06/2014.

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