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Author Topic: Selective enhanced FEC (again)  (Read 568 times)


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Selective enhanced FEC (again)
« on: August 07, 2018, 07:42:12 AM »

I have talked about this idea before. If you have a protocol that involves sending one-off packets, so no retransmission facility, or you may have a situation where it happens that one or more short packets are being sent at a time when there has not been recent history of a large number of such short packets sent back-to-back, then a smart modem that breaks layer separation or has a cross-layer 'hints' side channel that attaches metadata to outbound packets such metadata generated by a classifier, which is upper layer (L3+L4+other-) aware, whichever method anyway, the modem sends such packets using enhanced FEC, so more bloat. Thinking about pushing a modem too hard, with an inadequate SNRM, you could just about get away with it with TCP, although you might foolishly be throwing away small extra speed gains by needing very expensive TCP retx. But that is merely a performance tuning miscalculation. Stuffing up a UDP use-case that has not retx or having things like DNS lookup fail are disasters. This would keep you safe in the edge of reliability.

I have mislaid that earlier thread. What did we say before - a totally useless idea? L2 retx maybe removes the need for this, I am not sure. However, L2 retx has its limits and can of course fail, so where failure can not be tolerated under any circumstances, a very strong FEC application to give a huge extra margin, only where it is needed, could be the fix.