This preview shows page 1. Sign up to view the full content.
Unformatted text preview: RONIZATION
CHANNEL CODING DATA LINK LAYER PHYSICAL LAYER PHYSICAL LAYER Figure 2-1: Relationship with OSI Layers
2.1.2 PROTOCOL FEATURES
The TM Space Data Link Protocol provides the users with several services to transfer service
data units over a space link. To facilitate simple, reliable, and robust synchronization
procedures, fixed-length protocol data units are used to transfer data through the weak-signal, CCSDS 132.0-B-1 Page 2-1 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL noisy space links: their length is established for a particular Physical Channel (a single
stream of bits transferred over a space link in a single direction) during a particular Mission
Phase by management. These protocol data units are known as TM Transfer Frames (unless
otherwise stated, the terms ‘Transfer Frame’ and ‘Frame’ in this document refer to the TM
Transfer Frame). Each Transfer Frame contains a header which provides protocol control
information, and a fixed-length data field within which higher-layer service data units are
A key feature of the TM Space Data Link Protocol is the concept of ‘Virtual Channels’ (VC).
The Virtual Channel facility allows one Physical Channel to be shared among multiple
higher-layer data streams, each of which may have different service requirements. A single
Physical Channel may therefore be divided into several separate logical data channels, each
known as a ‘Virtual Channel’. Each Transfer Frame transferred over a Physical Channel
belongs to one of the Virtual Channels of the Physical Channel.
2.1.3 ADDRESSING There are three identifier fields in the header of Transfer Frames: Transfer Frame Version
Number (TFVN), Spacecraft Identifier (SCID), and Virtual Channel Identifier (VCID). The
concatenation of a TFVN and a SCID is known as a Master Channel Identifier (MCID), and
the concatenation of an MCID and a VCID is called a Global Virtual Channel Identifier
MCID = TFVN + SCID;
GVCID = MCID + VCID = TFVN + SCID + VCID.
View Full Document
- Spring '14