Accounting - Acct-Interim-Interval

Greetings, * We have added the attribute "Acct-Interim-Interval = 150" to the radgroupreply * However we are not getting accounting packets back on a 150sec frequency * We are getting the accounting packets on the start and stop of the connection * The reporting back (accounting packets), is that the responsibility og the NAS / RADIUS / Client ? Thanks Wynand