Cable television headend
The building is typically sturdy and purpose-built to provide security, cooling, and easy access for the electronic equipment used to receive and re-transmit video over the local cable infrastructure.
Analog terrestrial TV signals require a processor which is a RF receiver that outputs video and audio.
The mixed signals are sent into a broadband amplifier, then sent into the cable system by the trunk line and continuously re-amplified as needed.
Set-top boxes (STBs) or CableCards are required to receive these digital signals and are provided by the cable operator themselves.
Many modern cable systems are now "all digital" meaning analog video signals have been discontinued in order to reuse spectrum.
Most digital video signals are compressed to MPEG-2 and MPEG-4 formats in order to combine multiple video streams into a QAM making the most efficient use of spectrum which a customer cable set top box receives, demodulates, de-encrypts and displays as a virtual channel number that the viewer recognizes.
Most commonly in large nationwide cable systems a central or "super headend" is in service to feed a local hub via a fiber optic transport circuit.
In large cable systems, a provider may operate multiple super headends as a way of redundancy in the event of a failure.
Super headends also create a cost-effective environment for cable operators as the amount of equipment and faculties is greatly reduced and the signals can be replicated and transmitted to local hubs that feed a community or city.
Another benefit is the quick action of channel blackouts in certain areas during times of carriage contract disputes with broadcasters.
The RF from each service gets combined in the hub to ultimately a single coax cable broken down per node, but right before it leaves the hub to feed customers, gets changed to fiber optic light to feed local cable nodes which may cover a large building, a neighborhood or in rural areas, an entire community.
Cable nodes were initially intended to reduce amplifier cascade and improve signal quality to subscribers distant from a hub.
Depending on its geographic footprint and location, a hub may also receive local channels from neighbouring markets and combine them with the immediate market giving viewers from that particular hub multi-market programming, which the cable company may black out certain programming per carriage contract and FCC regulations.
An OTN's primary purpose is to extend the HFC cable plant to rural communities without having to locate on site, core network equipment such as a CMTS or video edge QAM devices.
The OTN relies on the parent hub (where the core network equipment is actually located) to provide the video and HSD services to its area.
