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Unformatted text preview: ts (MAPs)
attached to it by the Segmentation layer for the purpose of multiplexing user data
If multiplexing is not performed in the Segmentation layer (i.e., if only one
MAP is activated per Virtual Channel) or if the Segment Header is omitted
for a particular mission, then the Virtual Channel feature of the Transfer
layer provides an alternative method for multiplexing user data onto the
physical channel. Using this feature of the Transfer layer, up to 64
concurrent users may be multiplexed together by attaching each to its own
dedicated Virtual Channel during transfer through the physical channel.
However, since every open Virtual Channel has its own CLCW reporting
scheme, Virtual Channel multiplexing may increase the spacecraft reporting
The internal partitioning and use of the Virtual Channel field is mission-specified;
e.g., some of the bits may be allocated by a mission to form a “Spacecraft SubID”, which allows different spacecraft data handling chains to be addressed. (7) FRAME LENGTH (Bits 22 through 31)
This 10-bit field contains a length count “C” which equals one fewer than the total
octets in the TC Transfer Frame. The count is measured from the first bit of the
FRAME HEADER to the last bit of the FRAME ERROR CONTROL FIELD (if
present), or the last bit of the FRAME DATA FIELD if the error control is
omitted. The size of this field limits the maximum length of a TC Transfer Frame
to 1024 octets. The length count “C” is expressed as:
“C” = (Total Number of Octets) - 1 CCSDS 202.0-B-2 Page 4-6 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT
CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE The fifth octet of the FRAME HEADER contains the following field:
(8) FRAME SEQUENCE NUMBER (Bits 32 through 39)
The FRAME SEQUENCE NUMBER, which within this Recommendation is
denoted as N(S), is an up-counting binary number which is assigned to each TC
Frame by the TC Transfer layer, and which remains a viable entity only w...
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This document was uploaded on 03/06/2014.
- Spring '14