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I estimate that the average link in the UK network typically runs with a 10 percent packet loss rate. What’s more, we have to do it using a very low bandwidth. However, in the amateur packet radio network, error rates are many orders of magnitude greater, simply because we have to work with weaker signals, inferior equipment and poor sites. The designers assumption therefore was that a lost or corrupt packet was relatively rare, and there would be plenty of bandwidth to accommodate any re-sends. Although all packet-oriented protocols are designed to cope with lost or corrupt packets, in most cases they were designed for physical layers with very low error rates and high bandwidth, such as wire or microwave links. Datagram-mode TCP/IP is unworkable at such a loss rate. half duplex only achieves 50% of maximum for that mode. Causes serious loss of throughput with AX25, e.g. Average UK packet link runs at 10% packet loss rate (BER 1 in 10,000).
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Most packet-oriented protocols were designed for physical layers with very low loss / error rates. The system is so powerful that it can turn an unusable link into a good one. This presentation outlines the causes and effects of packet loss, then describes a very easy and low cost scheme for reducing packet losses, simply by using better software with the existing hardware. The performance degradation caused by these losses is many times greater than the rate of loss.
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Of all the packets launched into the ether, too many are simply lost, wasting a precious resource. In my view, the major limiting factor, regardless of link speed, is packet loss. However, the network as a whole does not perform well, and it would appear that the full potential of the network is not actually being realised. When you consider how many links there are in the UK Packet Radio network, and how little data there is to be moved, you would think that there would be plenty of spare capacity. It is powerful enough to make an unusable link into a good one. This presentation describes an available and very low cost scheme for reducing packet losses. Forward Error Correction for Amateur Packet Radio - A Software Solution Paula Dowie G8PZT 5th April 2003Ģ Introduction UK Packet network performs nowhere near its theoretical capacity.
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