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Unformatted text preview: enerated by the service provider.
2.2.4 RESTRICTIONS ON SERVICES
There are some restrictions on the services provided on a Physical Channel:
a) if the Master Channel Frame Service exists on a Master Channel, other services shall
not exist simultaneously on that Master Channel;
b) on one Master Channel, the Virtual Channel Frame Secondary Header Service shall
not exist simultaneously with the Master Channel Frame Secondary Header Service;
c) on one Master Channel, the Virtual Channel Operational Control Field Service shall
not exist simultaneously with the Master Channel Operational Control Field Service;
d) if the Virtual Channel Frame Service exists on a Virtual Channel, other services shall
not exist simultaneously on that Virtual Channel;
e) on one Virtual Channel, the Packet Service shall not exist simultaneously with the
Virtual Channel Access Service.
2.3 OVERVIEW OF FUNCTIONS 2.3.1 GENERAL FUNCTIONS
The TM Space Data Link Protocol transfers various service data units supplied by sending
users encapsulated in a sequence of protocol data units using services of lower layers. The
protocol data units, known as TM Transfer Frames, have a fixed length and must be
transferred over a Physical Channel at a constant rate.
The protocol entity performs the following protocol functions:
a) generation and processing of protocol control information (i.e., headers and trailers)
to perform data identification, loss detection, and error detection;
b) segmenting and blocking of service data units to transfer variable-length service data
units in fixed-length protocol data units; CCSDS 132.0-B-1 Page 2-10 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL c) multiplexing/demultiplexing and commutation/decommutation in order for various
service users to share a single Physical Channel;
d) generation and removal of idle data to transfer protocol data units at a constant rate.
The protocol entity does not perform the following protocol functions:
a) connection establishment and release;
b) flow control;
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- Spring '14