How does my satellite radio know what channels I may access?

The other day I activated a satellite radio in my car. Prior to activation I could listen to a few free channels. Afterwards, most of the channels were available. I am curious to know how it knows that I am allowed to listen to XM and to what channels I can listen, as I know there are premium stations available I do not get.

Thanks.

For those answering, I am a former EE major and 14 year IT veteran so an answer with some depth would be appreciated.

They send out a series of codes periodically that change or update the settings in recievers that are powered up.

Among those codes will be a code addressed to your specific radio, that is, a code that your radio will recognize is meant for it. Along with that address will also be data that tells the radio which channels are to be accessible.

2010 Chevrolet Malibu #R3966 in Franklin, MA 02038