This guide shows how to install and configure Smokeping on Debian Etch to monitor network latency.
Read more at Howtoforge
From the Smokeping web site: “SmokePing is a deluxe latency measurement tool. It can measure, store and display latency, latency distribution and packet loss. SmokePing uses RRDtool to maintain a longterm data-store and to draw pretty graphs, giving up to the minute information on the state of each network connection.”