The fiber optic network extends from the cable operators' master headend, sometimes to regional headends, and out to a neighborhood's hubsite, and finally to a coaxial cable node which serves anywhere from 25 to 2000 homes. A master headend will usually have satellite dishes for reception of distant video signals as well as IP aggregation routers. Some master headends also house telephony equipment for providing telecommunications services to the community.
A regional or area headend/hub will receive the video signal from the master headend and add to it the public, educational, and government access (PEG) cable TV channels as required by local franchising authorities or insert targeted advertising that would appeal to a local area. The various services are encoded, modulated and upconverted onto radio frequency (RF) carriers, combined onto a single electrical signal and inserted into a broadband optical transmitter.
This optical transmitter converts the electrical signal to a downstream optically modulated signal that is sent to the nodes. Fibre optic cables connect the headend or hub to optical nodes in a point-to-point or star topology, or in some cases, in a protected ring topology.
Fiber optic nodes
A fiber optic node has a broadband optical receiver, which converts the downstream optically modulated signal coming from the headend/hub to an electrical signal going to the homes. Today,[when?] the downstream signal is a RF modulated signal that typically begins at 50 MHz and ranges from 550–1000 MHz on the upper end. The fiber optic node also contains a reverse/return path transmitter that sends communication from the home back to the headend. In North America, this reverse signal is a modulated RF ranging from 5–42 MHz while in other parts of the world, the range is 5–65 MHz. The optical coupler combined with the optical receiver forms a node.[clarification needed]
The optical portion of the network provides a large amount of flexibility. If...