Ax.25 Protocol

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Issue : 1 Rev : 1 Date : 19/03/2007 Page : 1 of 11

Phase B/C

Telemetry and Telecommand Transfer Frames Format
Without uplink
Prepared by: Florian George

Checked by: Per Hemso (ESA/ESTEC) Ted Choueiri (EPFL)

Approved by:



ESA/ESTEC Noordwijk Netherland


19/03/07


Issue : 1 Rev : 1 Date : 19/03/2007 Page : 2 of 11

1 RECORD OF REVISIONS
ISS/REV 1/0 1/1 Date 15/03/2007 19/03/2007 Modifications Initial release Update after commentaries by Per Hemso Created/modified by Florian George Florian George

Ref.: S3-BC-SE-1-1b-AX.25 Transfer Frames Format.docx

Issue : 1 Rev : 1 Date : 19/03/2007 Page : 3 of 11

2 TABLE OF CONTENTS
1 2 3 RECORD OF REVISIONS ......................................................................................................................... 2 TABLE OF CONTENTS ............................................................................................................................. 3 REFERENCES ............................................................................................................................................. 4 3.1 3.2 4 5 6 APPLICABLE DOCUMENTS REFERENCES DOCUMENTS 4 4

LIST OF ACRONYMS ................................................................................................................................ 5 INTRODUCTION ........................................................................................................................................ 6 TRANSFER FRAMES FORMAT .............................................................................................................. 7 6.1 AX.25 TRANSFER FRAME FORMAT 6.1.1 Flag (8 bits) 6.1.2 AX.25 Transfer Frame Header (128 bits) 6.1.3 Information Field (0 to 2048 bits) 6.1.4 Frame-Check Sequence (16 bits) 6.2 TELEMETRY INFORMATION FIELD USAGE 6.2.1 Telemetry Transfer Frame Secondary Header 6.2.2 Data 6.2.3 Telemetry Transfer Frame Trailer 6.3 TELECOMMAND INFORMATION FIELD USAGE 7 7 7 8 8 9 9 10 11 ERROR! BOOKMARK NOT DEFINED.

Ref.: S3-BC-SE-1-1b-AX.25 Transfer Frames Format.docx

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3 REFERENCES
3.1 Applicable Documents
[A1] AX.25 Protocol Specification http://www.tapr.org/pdf/AX25.2.2.pdf

3.2 References Documents
[R1] [R2] [R3] [R4] [R5] ESA-PSS-04-106 ESA-PSS-04-107 CubeSat program Cyclic Redundancy Check Packet Telemetry Standard Packet Telecommand Standard http://cubesat.calpoly.edu/ http://en.wikipedia.org/wiki/Cyclic_redundancy_check

MEMO AX.25 Communication Mode, Ted Choueiri, 14/03/2007

Ref.: S3-BC-SE-1-1b-AX.25 Transfer Frames Format.docx

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4 LIST OF ACRONYMS
CCSDS CRC EGSE EPFL ESA ESOC ESTEC FCS GS ICD LMTS MSB SSID TBD TC TM UI-Frame VC Consultative Committee for Space Data Systems Cyclic Redundancy Check [R5] Electrical Ground-Support Equipment Ecole Polytechnique Fédéral de Lausanne (Swiss Federal Institute of Technology in Lausanne) European Space Agency European Space Operations Centre European Space Research and Technology Centre Frame-Check Sequence Ground Station Interface Control Document Microsystems for space technologies laboratory Most Significant Bit Secondary Station Identifier To Be Defined Telecommand Telemetry Unnumbered Information Frame (see [A1]) Virtual Channel

Ref.: S3-BC-SE-1-1b-AX.25 Transfer Frames Format.docx

Issue : 1 Rev : 1 Date : 19/03/2007 Page : 6 of 11

5 INTRODUCTION
This document describes the format of the Transfer Frames used for the mission. As the project will make use of the radio amateur network using radio amateur frequencies, the Transfer Frames must be compliant with the format defined in the AX.25 protocol [A1] which is used on theses equipments. After discussions and feedback from other CubeSat [R3] spacecraft development teams, it has been decided that only the Unnumbered Information Frames (UI-Frames) of the protocol will be used [R4]. To provide the necessary...
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