Transport Over HFC Network
By using frequency division multiplexing, an HFC network may carry a variety of services, including analog TV, digital TV (SDTV or HDTV), Video on demand, telephony, and high-speed data. Services on these systems are carried on radio frequency (RF) signals in the 5 MHz to 1000 MHz frequency band.
The HFC network can be operated bi-directionally, meaning that signals are carried in both directions on the same network from the headend/hub office to the home, and from the home to the headend/hub office. The forward-path or downstream signals carry information from the headend/hub office to the home, such as video content, voice and internet data.
The return-path or upstream signals carry information from the home to the headend/hub office, such as control signals to order a movie or internet data to send an email. The forward-path and the return-path are actually carried over the same coaxial cable in both directions between the optical node and the home.
In order to prevent interference of signals, the frequency band is divided into two sections. In countries that have traditionally used NTSC System M, the sections are 52 MHz to 1000 MHz for forward-path signals, and 5 MHz to 42 MHz for return-path signals. Other countries use different band sizes, but are similar in that there is much more bandwidth for downstream communication instead of upstream communication.
Traditionally, since video content was sent only to the home, the HFC network was structured to be non-symmetrical: one direction has much more data-carrying capacity than the other direction. The return-path was originally only used for some control signals to order movies, etc., which required very little bandwidth. As additional services have been added to the HFC network, such as internet access and telephony, the return-path is being utilised more.
Read more about this topic: Hybrid Fibre-coaxial
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