<P> In Digital Video Broadcasting, the Common Interface (also called DVB - CI) is a technology which allows decryption of pay TV channels . Pay TV stations want to choose which encryption method to use . The Common Interface allows TV manufacturers to support many different pay TV stations, by allowing to plug in exchangeable CAM modules for various encryption schemes . </P> <P> The Common Interface is the connection between the TV tuner (TV or set - top box) and the module (CAM) that decrypts the TV signal . The CAM module, in turn, then accepts the pay - to - view subscriber card, which contains the access keys and permissions . </P> <P> The host (TV or set - top box) is responsible for tuning to pay TV channels and demodulation of the RF signal, while CAM is responsible for CA descrambling . The Common Interface allows them to communicate with each other . All Common Interface equipment must comply with the EN 50221 - 1997 standard . This is a defined standard that enables the addition of a conditional - access module (CAM) in a DTV receiver to adapt it to different kinds of cryptography . The EN 50221 specification allows many types of modules but only the conditional - access module (CAM) has found popularity because of the pay TV market . Indeed, one of Digital Video Broadcasting's main strengths is the option of implementing the required conditional access capability on the Common Interface . </P>

What is a common interface card for tv
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