This six bit field enables up to 64 map addresses

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Unformatted text preview: ny one user from monopolizing the data transmission resource. This six-bit field enables up to 64 MAP addresses (from MAP 0 to MAP 63) to be associated with each Virtual Channel provided by the Transfer layer. Different TC User Data Units (e.g., separate TC Packets) arriving at the input to the Segmentation layer are allocated to a MAP. The segmentation and aggregation processes are conducted independently for each MAP. The resulting TC Frame Data Units from up to 64 MAPs are then multiplexed onto one Virtual Channel in accordance with user’s delivery priorities and instructions. Certain MAPs may have higher transmission priorities than others. CCSDS 202.0-B-2 Page 3-3 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE There are no restrictions on the selection of MAP Identifiers. In particular, MAPs are not required to be numbered consecutively. If multiple MAPs are not used on a particular Virtual Channel, but the Segment Header is otherwise required to be present, Bits 2 through 7 shall be set to a constant value for all TC Segments which are placed on that Virtual Channel. Segment Data Field. The Segment Data Field contains all or a portion of the higher layer TC User Data Unit (e.g., TC Packet) or an aggregation of TC Packets. The Segment Data Field length is variable with a maximum length of one octet less that the maximum length of the TC Frame Data Unit. 3.3 STANDARD PROCEDURES WITHIN THE LAYER Figure 3-3 illustrates the process of segmenting and aggregating TC User Data Units (in this example, TC Packets) and inserting them as TC Segments into TC Frame Data Units. The procedures are as follows. 3.3.1 SENDING END SEGMENTATION PROCEDURES The sending end of the Segmentation layer performs the following processing steps: (1) Allocates the TC User Data Unit to a particular Multiplexer Access Point. (2) If the TC User Data Unit (e.g., the TC Packet) exceeds a predetermined length, the Segmentation layer divides it into portions that are compatible with insertion into the TC Frame Data Unit and attaches a Segment Header to ea...
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This document was uploaded on 03/06/2014.

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