Problems in Accounting

Respected All, I face one problem with freeradius 2.6, When the client(Router) not send any accounting data (Cause of broke the connection between them) than freeRadius not off that account or in other words not logout that user in radacct. So, basically how can i off that particular account when data not coming from client(Router)? Warm Regard's Imdadali Kadiwala