The Cisco Persistent Storage Device (PSD) is an extension to existing storage for the Cisco Content Services Gateway (CSG) and Cisco Gateway GPRS Support Node (GGSN). It can receive and safely store CSG- and GGSN-generated call detail records (CDRs). The Cisco CSG or GGSN sends the CDRs to billing data collectors until the collectors are determined to be unreachable. The CSG or GGSN will then redirect the CDRs (including those not yet acknowledged of receipt by the data collectors) to the Cisco PSD.