Cop 1 provides two services sequence controlled

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Unformatted text preview: ervice data units supplied by the sending user are delivered to the receiving user. COP-1 provides two services (Sequence-Controlled Service and Expedited Service) to support these service types, as described in 2.2.1 and 2.2.2. 2.2.1 SEQUENCE-CONTROLLED SERVICE (AD SERVICE) The Sequence-Controlled Service (AD Service) is realized by an automatic ARQ procedure of the ‘go-back-n’ type, with sequence-control mechanisms of both sending and receiving ends and a standard report returned from the receiving end to the sending end. For the AD Service, COP-1 ensures with a high probability of success that: a) no FDU is lost; b) no FDU is duplicated; c) no FDU is delivered out of sequence. Two types of Transfer Frames are used for providing the AD Service: a) Type-AD Transfer Frames, for carrying FDUs; b) Type-BC Transfer Frames, for carrying Control Commands for configuring COP-1 (‘Unlock’ and ‘Set V(R)’). The AD Service is initiated by means of four distinct ‘Initiate AD Service’ Directives. Two of these Directives result in the transmission of one of the two Control Commands (Type-BC Transfer Frames). Each of the two Control Commands causes a well-defined action in FARM-1, which is then reflected in the CLCW. A timer is used to cause retransmission of the Control Command if the expected response is not received, with a limit on the number of automatic retransmissions allowed before it is declared that there is a problem in initiating the AD Service. The other two Directives allow the AD Service to be started without waiting for an action by the receiving end (although one requires receiving a good CLCW). Once COP-1 for a particular Virtual Channel has been initialized for AD Service, FDUs are inserted into Transfer Frames and transmitted on that Virtual Channel in the order in which they are presented to COP-1. The AD Service guarantees in-order delivery of FDUs on a single Virtual Channel. Because of the possibility of retransmission on only a single Virtual Channel, there is no guarantee CCSDS 232.1-B-2 Page 2-2 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 that FDUs on separat...
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