Unformatted text preview: tion of the communications services.
Physical Channel: a stream of bits transferred over a space link in a single direction. CCSDS 131.0-B-2 Page 1-3 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING space link: a communications link between a spacecraft and its associated ground system or
between two spacecraft. A space link consists of one or more Physical Channels in one or
1.6.2 NOMENCLATURE The following conventions apply for the normative specifications in this Recommended
a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;
b) the word ‘should’ implies an optional, but desirable, specification;
c) the word ‘may’ implies an optional specification;
d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.
NOTE – These conventions do not imply constraints on diction in text that is clearly
informative in nature.
1.6.3 CONVENTIONS In this document, the following convention is used to identify each bit in an N-bit field. The
first bit in the field to be transmitted (i.e., the most left justified when drawing a figure) is
defined to be ‘Bit 0’, the following bit is defined to be ‘Bit 1’, and so on up to ‘Bit N-1’.
When the field is used to express a binary value (such as a counter), the Most Significant Bit
(MSB) shall be the first transmitted bit of the field, i.e., ‘Bit 0’ (see figure 1-1).
BIT 0 BIT N -1 N -BIT DATA FIELD FIRST BIT TRANSMITTED = MSB Figure 1-1: Bit Numbering Convention
In accordance with standard data-communications practice, data fields are often grouped into
8-bit ‘words’ which conform to the above convention. Throughout this Recommended
Standard, such an 8-bit word is called an ‘octet’.
The numbering for octets within a data structure starts with ‘0’. CCSDS 131.0-B-2 Page 1-4 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 1.7 PATENTED TECHNOLOGIES The CCSDS draws attention to the fact that it is claimed that compliance with this document
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