The shoutcast log files show the bytes transferred upon closing of the connection. If they're enforcing limits, they're probably shutting down the sc_serv process when it exceeds a certain amount. However, if all the listeners are connected and never drop, it would be very easy to use double or triple the bandwidth in one period and it'd stay off the next month :/
There are also non-shoutcast servers (like icecast) that have better server-side configuration / limits and they're compatible with shoutcast and other sources.
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