STBs are devices that are connected to televisions at home. They connect a TV to an external signal source and transform the transmitted signal into video content, which is then displayed on the screen. The source may be cable, satellite, broadband, telephone line, or DSL connection. There are primarily two types of STBs, namely SD DTB and HD STB. HD STB has the ability to show both SD and HD channels as well as providing better sound and picture quality and greater viewing experience. HD STBs are further classified into four types: cable, satellite, IPTV, and hybrid STB. HD STBs also provide interactive services such as VOD, video conferencing, high-speed internet television, and/or home networking.