Hi Rein, My apologies if you were bothered by my use of the term naïve. Taking your statement on your web site at face value it is misleading. I have seen similar statements by other hams. Practice with space probes, digital TV, etc, also show the value of using FEC. ARQ introduces throughput degradation, also. Is there any information on the tradeoffs between FEC and AQR? Just as adaptive techniques are used with ARQ others can be used with FEC. Getting into DTN touches a key consideration because it approaches the problem from a different perspective. Packet erasure handling raises other questions that may lead to different lower level protocol solutions. Interesting work at http://planete-bcast.inrialpes.fr/rubrique.php3?id_rubrique=5 uses FEC at the packet level to reconstruct dropped packets. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://over50.k5rud.us/wiki/ -----Original Message----- From: Rein Couperus [mailto:rein@xxxxxxxxxxxx] Sent: Saturday, February 24, 2007 3:16 AM To: Walt DuBose; Rud Merriam Cc: linlink@xxxxxxxxxx; pskmail@xxxxxxxxxxxxx Subject: Re: Call for comments on open protocols All this is theory. FEC is going to bring relief in only 1% of practical cases only, viz. in the extreme case when you are on the borderline between copy and no copy. In normal practise (and we have gathered some during 2 year's operation of pskmail servers), you are either fighing the S9+20 pactor station which comes on your frequency , or 80 dB QSB in multi-path situations, or S9+20 static crashes in case of QRN. Sometimes these 3 effects appear simultaneously. This is nothing where FEC can help out, maybe only when you use extreme time diversity. And with extreme I mean at least 5 seconds apart, equally sending everything twice a priory. If practise is naive, than this is naive. The gaps in the stream are not something you can repair with some degree of FEC, they are just too wide. The only way is a lossless arq mechanism, where the holes in the stream are detected and filled in afterwards. One thing we have not yet added to the protocol is memory receive, which combines the information in the frames to build a valid one in case also the repeat is damaged. This, combined with a block length which adapts to the qrm characteristics guarantees an optimum adaptation to the actual situation on the band. FEC is only going to slow all this down. We have compared MT63-2k with PSK63 and found no increase in throughput on the band. And if you compare the bandwidth/throughput efficiency ratio the MT63-2 case looses by a factor of 10. It is just a case of throwing precious spectrum away. Summing it up, we'd better worry about DTN (delay tolerant network) technologies which work around qrm and qsb than about scratching the last dB out of the protocol. 73, Rein EA/PA0R/P