India Broadband Forum

rupu1983

One of the technology that transporting VOD/NVOD services, as well as well as standard and expanded cable services, is hybrid fiber coax(HFC). In such system, the service provider typically uses the fiber optic transport, often a fiber loop to provide redundancy, from the cable head end(satellite downlink, SONET terminal etc) to a ‘pedestal’ at which the digital signal on the fiber is translated to an analog signal for the retransmission to the customer over standard co-axial cable. A pedestal typically serves 500 homes. The roughly 745 MHz bandwidth of the cable is distributed some what likes.

• 5-50 MHz (35 MHz bandwidth) –upstream (reserve direction)

• 54-550 MHz (496-MHz bandwidth) –standard cable 6-MHz RF channels (approximately 80-85)

• 550-750 MHz (200 MHz bandwidth) –digitized (4- or 6- Mbits/s) video modeling RF signals using 64 QAM (or eventually 256 QAM) modulation and orthogonal frequency division multiplexing (OFDM). 64 OAM provides approximately 8-Gbits/s digital bandwidth for 2000 4-Mbit/s channels.

The upstream bandwidth is used for VOD/NVOD control functions, status monitoring (status of viewing pay-per-view channels), two-way telephony, high speed data transfer, via cable modems, and so on. The standard cable bandwidth is used for basic and premium cable and pay-per-view cable services. The digital bandwidth is used for VOD/NVOD delivery, interactive television services expanded cable services, multimedia services, and so on. That the digital channel require a STB converter to convert QAM( quadrature amplitude modulation) signal into an analog signal. The STB also require for the upstream control functions and status monitoring.
Observe the HFC network must be extremely reliable particularly because of the telephony services they provide. Network which provide telephony service, for example are consider to be subscriber ‘lifeline‘services.

A competing, but similar, technology is called fiber-to-the-curb (FTTC). In this system, the optical fiber is extended to pedestal, as in HFC. The pedestal, however, serves pockets of 18 to 24 homes with twisted pair cable at the substantial reduced bandwidth. FTTC is substantially more expensive than HFC.