Most of the VoIP User core network is constructed using industry-standard PC servers, running Linux and telephony applications that include Asterisk (for audio messaging media and echotesting services), OpenSER (for SIP proxy and registrar duties) and edge controllers and media gateways being a combination of open-source and custom written software. Call rating, CDR collection and account handling software is custom written and based on FreeRADIUS and the integration of RADIUS messaging to the media gateways and SIP B2BUAs residing at the network edge. VoIP User currently operates 9 servers hosted globally and with the main core and media gateways residing at Telehouse London.