Throughput of ADSL Modems

Abstract

This paper considers the throughput of ADSL (Asymmetric Digital Subscriber Line) modems, used for high speed data transmission over relatively unreliable connections, e.g., copper telephone wires. The modem technique uses an error correcting code and interleaving. The settings include a grouping factor S which affects the amount of data per code word, the number of redundant bytes per code word (R) and the interleave depth D. The influence of these parameters on both the effective data transmission rate and the resulting error rate in the received signal are determined for two error situations: random errors and burst of errors. An approximate analysis for the random error case of the throughput of a TCP (Transport Control Protocol) connection using an ADSL modem shows that maximum throughput is obtained for the highest values of S and R.