{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}


Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
I.B. + M.A. DE LANDE LONG SOFTWARE + CONSULTANCY Options for repeated retransmissions for telecommand Page 1 TCretrans7 2008Sep09 Options for Repeated Transmissions of TC Transfer Frames 1. Introduction This document considers the options for the specification of systematic retransmissions of TC Transfer Frames, under the control of a new parameter in the CCSDS telecommand protocol. 1.1 Related CCSDS standards The following CCSDS recommended standards (Blue Books) are relevant to the telecommand retransmissions discussed in this document: TC Synchronization and Channel Coding, CCSDS 231.0-B-1, September 2003 TC Space Data Link Protocol, CCSDS 232.0-B-1, September 2003 Communications Operation Procedure-1, CCSDS 232.1-B-1, September 2003 1.2 COP-1 The Communication Operations Procedure 1 (COP-1) is in the Transfer Sublayer of the Data Link Layer of the CCSDS telecommand communication protocol stack. It provides two data transfer services called the sequence-controlled service and the expedited service. COP-1 uses three types of Telecommand Transfer Frames, which are indicated by flags in the frame header: Type-AD frames carry data for the sequence-controlled service. During operation of the service, there can be many type-AD frames outstanding (unacknowledged). This document is principally concerned with the systematic retransmission of type-AD frames. Type-BC frames carry control commands for the sequence-controlled service. They can be used when starting a session for the sequence-controlled service, as part of the process for ensuring that the sender and receiver are correctly synchronized for their use of sequence numbers. There is never more than one type-BC frame outstanding. The application of the systematic retransmission to type-BC frames is also considered. Type-BD frames carry data for the expedited service. They are not retransmitted, and any new systematic retransmission mechanism that is introduced for type-AD frames should ensure that it does not result in the retransmission of type-BD frames.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
I.B. + M.A. DE LANDE LONG SOFTWARE + CONSULTANCY Options for repeated retransmissions for telecommand Page 2 TCretrans7 2008Sep09 1.3 Purpose of the systematic retransmissions The systematic retransmission is intended to improve the efficiency of COP-1 for deep space missions on links with long light delays. The COP-1 protocol includes an automatic retransmission mechanism which works very well for near-Earth missions: the total round-trip delay is short so COP-1 can respond efficiently to the need for retransmission of a lost frame. For deep space missions the round-trip delay is long and the COP-1 response is not efficient. As discussed below, the existing COP-1 parameters can be manipulated to force early automatic retransmissions for a deep space mission.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}