Unformatted text preview: dentify 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). CCSDS 132.0-B-1 Page 1-4 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL BIT N–1 BIT 0 N-BIT DATA FIELD FIRST BIT TRANSFERRED = MSB Figure 1-1: Bit Numbering Convention
In accordance with standard data-communications practice, data fields are often grouped into
eight-bit ‘words’ which conform to the above convention.
Recommendation, such an eight-bit word is called an ‘octet’.
The numbering for octets within a data structure starts with zero. By CCSDS convention, all
‘spare’ bits shall be permanently set to ‘0’.
1.7 REFERENCES The following documents contain provisions which, through reference in this text, constitute
provisions of this Recommendation. At the time of publication, the editions indicated were
valid. All documents are subject to revision, and users of this Recommendation are
encouraged to investigate the possibility of applying the most recent editions of the
documents indicated below. The CCSDS Secretariat maintains a register of currently valid
Information Technology—Open Systems Interconnection—Basic Reference Model:
The Basic Model. International Standard, ISO/IEC 7498-1. 2nd ed. Geneva: ISO,
1994.  Information Technology—Open Systems Interconnection—Basic Reference Model—
Conventions for the Definition of OSI Services. International Standard, ISO/IEC
10731:1994. Geneva: ISO, 1994.  Cor. 1  TM Synchronization and Channel Coding. Recommendation for Space Data System
Standards, CCSDS 131.0-B-1. Blue Book. Issue 1. Washington, D.C.: CCSDS,
September 2003.  “Registries.” Space A...
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