Ccsds 2020 b 2 page a 6 ccsds historical document

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Unformatted text preview: ained in a CLCW, that the receiving end of the Transfer layer has encountered congestion in passing data to the layer above and cannot accept any more Type-A frames. CCSDS 202.0-B-2 Page A-6 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE ANNEX B DATA ROUTING SERVICE SPECIFICATION (THIS ANNEX IS PART OF THE RECOMMENDATION) Purpose: This Annex provides the detailed specification of the service provided by the Segmentation and Transfer layers. CCSDS 202.0-B-2 Page B-1 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE B-1 OVERVIEW OF THE LAYERS WITHIN THE DATA ROUTING SERVICE The Data Routing Service is implemented using two layers of protocol: the Segmentation layer and the Transfer layer. The function of the Segmentation layer is to prepare user telecommand messages for transmission to the spacecraft, using services of the Transfer layer, by forming them into TC Frame Data Units. The function of the Transfer layer is to reliably move Transfer Frames from the sending end of the Telecommand System to the receiving end, using the Channel Service, including retransmission of any frames which were found by the receiving end to have been damaged or lost during transfer. A diagram defining the principal elements within the Data Routing Service is presented in Figure B-1. Higher-layer TC User Data Units (e.g., TC Packets) may range in length from very short units to very long ones. The characteristics of the physical data channel which interconnects the sending and receiving end of the system are such that the most effective method of transmission requires intermediate length (up to 8 k bit) data structures (see Reference [2]). Furthermore, since this physical data channel has a finite data-carrying capacity, a method must be provided to prevent one user from monopolizing the channel to the exclusion of others. The task of the Data Routing Service is therefore to provide the transformation between the characteristics of the user layers of the TC System and the constraints of the physical channel, including breaking large user messages into smaller communicationsoriented pieces or a...
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This document was uploaded on 03/06/2014.

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