232 internal organization of protocol entity figures

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Unformatted text preview: on of protocol data units. 2.3.2 INTERNAL ORGANIZATION OF PROTOCOL ENTITY Figures 2-5 and 2-6 show the internal organization of the protocol entity of the sending and receiving ends, respectively. Data flow from top to bottom in figure 2-5, and from bottom to top in figure 2-6. These figures identify data-handling functions performed by the protocol entity and show logical relationships among these functions. The figures are not intended to imply any hardware or software configuration in a real system. Depending on the services actually used for a real system, not all of the functions may be present in the protocol entity. Packet Serv ice VC Acces s Serv ice VC _FS H Serv ice VC _O C F Serv ice VC Frame Serv ice Packet MC _FS H Proces s ing Serv ice MC _O C F Virtual C hannel G eneration Serv ice MC Frame Virtual C hannel Multip lex ing Serv ice Mas ter C hannel G eneration Mas ter C hannel Multip lex ing All Frames G eneration Figure 2-5: Internal Organization of Protocol Entity (Sending End) CCSDS 132.0-B-1 Page 2-11 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL Packet Serv ice VC Acces s Serv ice VC _FS H Serv ice VC _O C F Serv ice VC Frame Serv ice Packet MC _FS H Ex traction Serv ice MC _O C F Virtual C hannel Recep tion Serv ice MC Frame Virtual C hannel Demultip lex ing Serv ice Mas ter C hannel Recep tion Mas ter C hannel Demultip lex ing All Frames Recep tion Figure 2-6: Internal Organization of Protocol Entity (Receiving End) By extracting multiplexing/demultiplexing and commutation/decommutation functions from figures 2-5 and 2-6, the relationship among various data units can be shown as figure 2-7, which is known as the Channel Tree of the TM Space Data Link Protocol. In figure 2-7, multiplexing (shown with a triangle) is a function of mixing, according to an algorithm established by the project, multiple streams of data units, each with a different identifier, to generate a single stream of data units. Commutation (shown with a box) is a function of concatenating, according to the formatting rule specified by the protocol definition, multiple data units, each from a different service, in a single protocol data unit sharing the sam...
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