Tcretrans7 2008sep09 ib ma de lande long software

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Unformatted text preview: mes. TCretrans7 2008Sep09 I.B. + M.A. DE LANDE LONG SOFTWARE + CONSULTANCY Options for repeated retransmissions for telecommand Page 2 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. For a sequence of frames ABCDEF…, the COP-1 automatic retransmission results in a cyclic transmission pattern of the form: ABCDEF…ABCDEF…ABCDEF… This document considers the options for adding a new function under the control of a new parameter: With the proposed new parameter, the user of the protocol would be able to force the transmission of type-AD frames a specified number of times, instead of only once. The specified number of systematic retransmissions would be used at every transmission attempt. For a sequence of frames ABCDEF…, the systematic retransmission would result in a hammer transmission pattern of the form: AAABBBCCCDDDEEEFFF… When frame loss errors are sporadic, the hammer pattern is an advantage: because the errors are sporadic, they are less likely to hit all the repeats of a frame. With cyclic transmission pattern and sporadic errors, successful reception of a sequence of frames depends on where the errors fall within a cycle. For example, a frame loss of an early frame in the first cycle causes the remaining frames in that cycle to be rejected. The advantage of the hammer pattern over the cycle pattern increases as the number of frames in the sequence increases. Example of sporadic errors and cyclic transmission pattern: Fram...
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