Conditional Access System (CAS)

A conditional access system (CAS) is a system by which electronic transmission of digital media, especially satellite television signals through cable, is limited to subscribed clients. This is called conditional access. The signal is encrypted and is unavailable for unauthorised reception. A set-top box containing a conditional access module is required in the customer premises to receive and decrypt the signal.

A conditional access system comprises a combination of scrambling and encryption to prevent unauthorized reception. Scrambling is the process of rendering the sound, pictures and data unintelligible. Encryption is the process of protecting the secret keys that have to be transmitted with the scrambled signal in order for the descrambler to work. After descrambling, any defects on the sound and pictures should be imperceptible, i.e. the conditional access system should be transparent. The primary purpose of a conditional access system for broad-casting is to determine which individual receivers/set-top decoders shall be able to deliver particular programme services, or individual programmes, to the viewers.

An addressable system is defined under the provisions of the Act as follows:

"addressable system" means an electronic device or more than one electronic devices put in an integrated system through which signals of cable television network can be sent in encrypted or unencrypted form, which can be decoded by the device or devices at the premises of the subscriber within the limits of authorisation made, on the choice and request of such subscriber, by the cable operator to the subscriber;"

As per the provisions of the Act, the Government has issued notifications under which the Government has introduced Conditional Access System initially in certain parts of the metro cities of Delhi, Mumbai and Kolkata and in the entire city of Chennai.

The cable operators in these areas have been directed to make available set top boxes/ addressable system to the consumers on demand for accessing "pay channels", while the "free to air" channels could be aired in the current receivable mode, without a set top box. These set top boxes are of two kinds:

(i) Analog Set Top Box
(ii) Digital Set Top Box

The cable television subscribers in these areas can currently view free to air channels by making a payment of Rs.72/- per month to their local cable operator while for accessing pay channels they are required to buy a set top box from their cable operators and further make monthly payments for the pay channels that the subscriber wishes to watch apart from making a payment of Rs. 72/- for basic free to air services. The amount for pay channels would be Rs. 5 per channel.

CAS is now becoming a significant concern for major companies in the DVB-H market because broadcasters are looking to control the digital signals that they will be broadcasting.

References: www.corecentre.org/guest/focus/default.asp, www.en.wikipedia.org/wiki/Conditional_access_system