The data routing service contains two distinct layers

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: l Service to perform its functions. The Data Routing Service contains two distinct layers of data handling operations: (1) A SEGMENTATION layer, which prepares the user data units for transfer by forming them into suitable-sized routable pieces and permitting these pieces to be multiplexed together for transmission through the command channel. (2) A TRANSFER layer, which encapsulates the routable pieces of user data into transfer data structures and controls their transmission through the channel, including any retransmissions needed to ensure delivery of the routable pieces in sequence without gaps or duplication. The detailed specification of the retransmission mechanism, called the Command Operation Procedure, is given in Part 2.1 of the Telecommand Recommendation (Reference [7]). The Data Routing Service provides an interface between the high-layer “user” elements of the TC System and the low-layer communications channel through which data flow. Because the underlying Channel Service inherently includes a noisy signal path, there is a finite probability that it will introduce an error. Since any error in the user’s data will render them invalid, it is desirable to break large user data units into relatively small pieces (which will thus each have a lower probability of being invalidated by transmission error than if the entire user data unit were sent contiguously). This improves system throughput efficiency since only small pieces have to be retransmitted when errors are detected. However, there may also be situations in which the user data units are very small. For efficient transfer, the Data Routing Service provides the capability to group these small units into larger pieces. Analysis of the performance of the Channel Service and Data Routing Service under various conditions is contained in Reference [2]. CCSDS 202.0-B-2 Page 2-1 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE APPLICATION PROCESS LAYER TELECOMMAND, PART 3: DATA MANAGEMENT SERVICE COMMAND DIRECTIVE SYSTEM MANAGEMENT LAYER TC APPLICATION DATA PACKETIZATION LAYER TC USER DATA UNIT SEGMENTATION LAYER TELECOMMAND, PART 2: DATA ROUTING SERVICE TC FRAME DATA UNIT TRANSFER LAYER TC TRANSFER FRAME CODING LAYER COMMAND LINK TRANSMISSION UNIT TELECOMMAND, PART 1: CHANNEL SERVICE PHYSICAL LAYER PHYSICAL WAVEFORM Figure 2-1: Telecomm...
View Full Document

Ask a homework question - tutors are online