The headend collects signals from several sources, processes them and broadcasts them to the cable network.
Contents of the article series
- Part 9: Headend
- Part 10: Troubleshooting on the cable TV network
HabrΓ© already has a wonderful article about the headend device: . I will not rewrite it in my own words and simply recommend that those who are interested read it. A description of what I have in charge would turn out to be less interesting, because we do not have such a variety of equipment, and all signal processing is handled by the AppearTV chassis with various expansion cards, the variety of which allows all the functionality to fit in several four-unit chassis.
Image from website
These devices allow you to control all processes through a functional web interface, which depends on the hardware content of the chassis.
In addition, we do not collect the terrestrial signal, so the antenna post looks something like this:
Image from the forum I was not allowed to upload a real photo of our station.
Such a number of dishes is necessary to receive channels from several satellites at the same time.
The satellite signal is usually closed by scrambling: this is a type of encryption in which the symbols of the sequence are mixed according to a given algorithm. This does not require a lot of computing power and execution time, which means that the signal is processed without delay. In hardware form, the subscriber ID (even if it is a provider that transmits the signal further to its network) is a familiar card with a chip that is inserted into a conditional access module (CAM) with a CI interface, the same as in any modern TV.
Actually, all the mathematics is performed inside the module, and the map contains a set of keys. The operator can encrypt the stream with keys that the card knows (and the operator himself wrote them into the card) and, thus, manage the set of subscriptions up to the complete disconnection of the card from the system by changing the main "operator's" identifier. This is just a general description of the operation of conditional access systems, in fact there are many different ones: on the one hand, they are constantly hacked, and on the other, the algorithms are complicated, but thatβs a completely different storyβ¦
Since the operator also provides paid channel packages in its network, it is therefore necessary to encode them before transferring them to the network. This task is performed by the equipment of a third party provider of conditional access system, which provides it to the operator as a service. The equipment installed at the headend ensures the functioning of the system of conditional access to content: both encryption and control of keys registered in smart cards.
PS So no one helped me with an article on DOCSIS, if anyone has a desire, I will be glad, write.
Source: habr.com