Unformatted text preview: and System CCSDS 202.0-B-2 Page 2-2 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE NOTE A: Figure 2-1 represents a logical view of the TC System, and physical
implementations may not necessarily correspond to the sequential flow of
operations implied by the figure.
NOTE B: This Recommendation primarily specifies the data structures and protocols
flowing ACROSS the layers of the TC System, since these have a direct impact
on the long lead-time design of future spacecraft hardware and software.
Comprehensive definition of the associated flow of control instructions, which
are required to initialize the layers and to direct the flow of TC data units
BETWEEN the layers, remains an item for potential future extension of this
document. NOTE C: Although the layers defined in this document may be used without necessarily
implementing those defined in the Channel Service (Reference ) and Data
Management Service (Reference ), the names of the layers in those Services
will be used to denote the external interfaces for the Data Routing Service, when
appropriate. CCSDS 202.0-B-2 Page 2-3 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE 3 SEGMENTATION LAYER: STANDARD DATA STRUCTURES
AND PROCEDURES 3.1 OVERVIEW OF THE LAYER The data unit received by the Segmentation layer from the higher layer is called a “TC User
Data Unit”. If the higher layer is the Packetization layer, defined in Reference , it will be
a TC Packet; otherwise, it may be any other user-provided data unit.
The data unit passed from the Segmentation layer to the Transfer layer is the “TC Frame Data
Unit”. It will normally consist of a TC Segment. If neither segmentation nor multiplexing is
used on a particular Virtual Channel, the Segment Header may be omitted on that Virtual
The TC Segmentation layer accepts variable-length TC User Data Units from the layer above
and prepares them for transmission by the layers below by:
(1) forming the TC User Data Units into TC Frame Data Units, which are compatible
with insertion into the data field of the TC T...
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