Skype uses a proprietary Internet telephony (VoIP) network called the Skype protocol. It is sometimes used for two circuits, such as 4-wire telephony and other telecommunications applications. Telkom has major businesses in fixed line telephony, internet and data communications. Prior to cellular mobile telephony, there was mobile radio telephony. Optical communication provides the backbone for both the Internet and modern telephony. Private sector companies operate in mobile telephony, long distance telephony and Internet access. These solutions support a wide range of organizations with IP telephony networks. Use of the term has continued in telephony and data communications. The widest deployment of video telephony now occurs in mobile phones. BSNL Landline is the largest fixed-line telephony in India. This is inclusive of voice telephony, voicemail, data services and GSM-based services. Radiolocation in cellular telephony uses base stations. Nordic Mobile Telephony (NMT) was an early provider of international roaming. Under Bekker, Naspers invested in pay television, mobile telephony and various internet services. Radio frequencies are also applied in carrier current systems including telephony and control circuits.