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Modem Speed Monitoring in a Multispeed Modem Network

IP.com Disclosure Number: IPCOM000052542D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Thirion, P: AUTHOR

Abstract

This article describes a method of monitoring the modem speed in a network in which each modem is provided with nominal and fall-back speeds, based on the measurement of a normalized line quality.

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Modem Speed Monitoring in a Multispeed Modem Network

This article describes a method of monitoring the modem speed in a network in which each modem is provided with nominal and fall-back speeds, based on the measurement of a normalized line quality.

One approach to characterize the quality of the signal received from the line consists of measuring the quadratic error, which is the average distance the received signal misses the theoretical target point. The bit error rate (BER) is strongly related to line quality Q; the smaller Q is, the lower is the bit error rate.

Let Q(o) be the line quality corresponding to a BER of 10/-5/ when the modem operates at its nominal speed. If Q < Q(o), BER at nominal speed will be less than 10/-5/; If Q > Q(o), BER at nominal speed will be greater than 10/-5/.

Assuming that noise immunity is about 6 dB higher at fall-back speed than that at nominal speed, we will have: If Q < 2Q(o), BER at fall-back speed is less than 10/-5/; If Q > 2Q(o), BER at fall-back speed is greater than 10/-5/.

Since Q(o) depends on the modem type and a network may comprise various modem types, it is convenient to define "normalized line quality" as: L = K(o) Q with K(o) = 1 over Q(o).

Whenever a modem is requested by the host system to perform a line quality measurement, it measures Q and encodes the normalized line quality in accordance with its operating speed, which is sent to the host, together with a bit indicating its operating speed.

The host syste...