On Wednesday 07 March 2007 00:29, Rony wrote: > True! That's why we need to think of a reliable transmission method.
> Devdas Bhagat wrote: > > Reliability implies two way communication, or massive > > retransmits. You can get one way satellite traffic working, at > > rates cheaper than those provided by a dedicated wired circuit. > > > > You need a DVB and a satellite hookup. I suggest talking to > > Teleglobe ^WVSNL about this. > > Thanks for all the information. I will work on it. Refer to CCITT red book before reinventing a square wheel. Besides all the points in DB's mail, you need to get a very high SNR for any usable bw. You dont just toss your dish on the terrace and expect it to work. Even with all the fine tuning you get high ber which would make any loss less transmission at the bandwidths required impossible. In the case of syncd systems (TV and dvb reciever) the dvb reciever can recover from a few bits of error per block. If not it will fill a few lines between hsync with junk, often visible as a dislocated body part. If the error is more severe the screen will lock until it resyncs with an error free frame. Similiar effects can be seen in a video conference. With your system even with a 2 Mbps down link it's going to take 5 hrs for a dvd. There will be inumerable errors, including ones caused by random things crossing the los. You will have to wait 5hrs for recieveing an error block with every chance that there will be errors again in the same blocks - happened all the time in the ecc mode of facsimile communications, which was meant to solve exactly the same problem partial retransmission of error blocks at the end of a reception AFTER the receving end requested retransmission of the error block. The net result was that the ECC mode invariably took 4 times longer than non ecc mode. If you set it to night transmission you would have a fat bill in the morning. Btw i along with others wrote the entire facsimile stack by reading the red book. Your problem is not in writing a protocol at all, but in the innumerable problems of cost, performance and reliability caused by natural phenomena. More readily solved by modem algos rather than communication protocols (which would acutally worsen the problem). -- Rgds JTD -- http://mm.glug-bom.org/mailman/listinfo/linuxers
