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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 CCSDS 202.0-B-2 Page A-6 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT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 CCSDS 202.0-B-2 Page B-1 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT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
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 ).
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.
- Spring '14