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Unformatted text preview: w data rate. For handling an emergency with a near-Earth spacecraft, the COP-1 expedited service can be
sufficient, with telecommand frames managed one by one. For these deep-space scenarios, the
proposed systematic retransmissions provide another means to attempt to deliver a sequence of
telecommand frames, despite the very difficult conditions. 1.4 Scope of the systematic retransmissions
The systematic retransmission is in addition to the existing automatic retransmissions of the sequencecontrolled service.
Any changes to support the systematic retransmission mechanism will be limited to the sending end of
the telecommand communications system. The desired effect of the retransmissions relies on the
existing behaviour of the receiving end. The discussion in this document is therefore only concerned
with the sending end of the frames for the sequence-controlled service.
The expedited service of COP-1 has no retransmission mechanism: FOP-1 transmits each frame
exactly once. The proposed systematic retransmission does not affect the expedited service.
It is very important to limit the scope of the modifications and the impact on existing standards. The
specifications associated with the new parameter should be designed to be compatible with existing
implementations, so that existing compliant implementations remain compliant with the modified
standards. The behaviour of a modified system with the default value of the new parameter should be
identical to an unmodified system. TCretrans7 2008Sep09 I.B. + M.A. DE LANDE LONG
SOFTWARE + CONSULTANCY
Options for repeated retransmissions for telecommand Page 4 2. Background
2.1 COP-1 automatic retransmissions
The sequence-controlled service includes a mechanism for the automatic retransmission of a sequence
of TC Transfer Frames whenever one of them is not correctly received on board. The retransmission
mechanism is “go-back-n”.
COP-1 uses protocol status information which is passed from FARM-1 (the receiving end of COP-1) to
FOP-1 (the sending en...
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This document was uploaded on 03/06/2014.
- Spring '14