An IP phone uses Voice over IP technologies allowing telephone calls to be made over an IP network such as the internet instead of the ordinary PSTN system. Calls can traverse the Internet, or a private IP Network such as that of a company. The phones use control protocols such as SIP (Session Initiation Protocol), SCCP (Skinny Client Control Protocol) or one of various proprietary protocols such as that used by Skype. IP phones can be simple software-based Soft phones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone. There also exists the possibility to reuse ordinary phones as IP phones, with analog telephony adapters (ATA).