Home Latin America I 2000 Cable Telephony

Cable Telephony

by david.nunes
Jose Carlos Pereira da CunhaIssue:Latin America I 2000
Article no.:5
Topic:Cable Telephony
Author:Jose Carlos Pereira da Cunha
Organisation:CTBC Telecom
PDF size:20KB

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Article abstract

Cable Telephony technology allows the use of cable networks, including hybrid fibre cable (HFC) networks, for two-way dial-up telephony. Telephone companies can build their own cable network, but by renting existing networks from it from a CATV operator, and adapting it for two-way connections costs can be shared and the investment needed greatly reduced.

Full Article

The figure below compares the time needed to implement phone service in Brazil when different technologies are used (Conventional drop, Cable Telephony System, Wireless Local Loop, and Specialized Limited Service). Licenses for conventional drop (wired telephone service) or WLL technologies is currently limited by law; full open competition is not yet permitted. By obtaining “Specialized Limited Service” licenses and using Cable Telephony faster start-up of new telephone services is possible which provides such additional advantages as semi-permanent connections, data transfer private channels, and broadcast CATV signals distribution. AT&T followed this route after its network was divided among the baby bells. Having lost the right to provide local services, the company was obligated to pay local operating companies up to 40% of revenues on long distance calls. As a way to immediately gain an access network, AT&T bought TCI, with 10 million customers across the United States and an inplace 55 billion dollars infrastructure. They then made a deal with MediaOne owner, TIME WARNER, to reach another 20 million customers throughout the US. By financing the rebuilding and expansion of the network and paying Time Warner a monthly fee AT&T obtained access to customers and transmission facilities at a far lower cost than the 40% of revenues they had to pay to local companies. It was an even better deal for the CATV companies that got extra revenue by providing new services using their installed physical structure. Cable telephony technology optimizes the use of existing CATV networks, providing telephone services to customers in areas where conventional networks are not yet present and providing rapid coverage of new areas. Cable telephony technology does not compete directly with conventional network solutions, it aggregates value for customers who need fast and effective services. Subscriber TV systems use coaxial cabling to transmitting video and audio signals. These systems have technical limitations regarding the distance over which signals can be transmitted if signal quality is to be maintained. To extend the range of acceptable transmission as many as 12 amplifiers used to be installed between the video hub, the so-called Head End, and the subscribers home. It was expensive to install and maintain the many amplifiers needed to provide wide coverage. HFC (Hybrid Fibre Coax) technology allows the replacement of coaxial network backbones with glass fibre cables. Fibres link the central site to a neighbourhood hub, and coax cables connect the hub to the homes. The number of households that can be covered by a cable TV network is quantified by a statistic called HP or Homes Passed. Typically, an HFC network has between 2000 and 2500 HPs per link for a one-way only (from Head End to subscribers home) system. It is necessary to adapt the whole network, so that two-way communications, telephone service and full interactive access to broadband signals, interactive TV, internet access and other digital services can be delivered. By increasing interactivity, though, the number of subscribers decreases to between 400 and 500 per link. How does a Cable Telephony system work? The conventional system of cable TV has a Head End, where the signals, usually captured through satellite, are injected into the networks optical backbone to hubs for re-distribution through coaxial cables to homes throughout the region. A Cable Telephony System allows telephone signals to be transmitted, along with TV signals, in the same optical fibre / coaxial cable network. A Host Digital Terminal (HDT), receives input signals from both the telephone commutation central site and from the Head End itself. The signals are combined and transmitted through glass fibre to a Multi Voice Port (MVP) at or near the final destination where the compound signal is split apart into its component parts. From that point conventional telephone drop pairs carry the conversation and coaxial cables carry the cable TV signals, as illustrated above. The cable TV system uses bandwidths of 54 MHz to 750 MHz to transmit video channels to subscribers. Cable TV broadcast signals are one way and, for the most part, analogue. Only recently have some cable TV companies begun to provide digital video transmission. Telephone communications, coming from the central site (distribution centre) to which the Cable Telephony system is linked, have to be divided into two channels, given the one-way connection used in cable TV and inserted into the frequency band of one of the video channels. For communication from the subscriber to the central site, Cable Telephony systems use the frequency band between 5 MHz and 42 MHz. This is called the return band by cable TV companies. The return band, normally used for receiving information coming from the equipment installed at the subscriber site, provides interactivity and access to services such as the Pay per View. This same frequency band is also used by network equipment to transmit system monitoring telemetry data. The frequencies and bands in the system are shown above. Conclusion CTBC Telecom is currently testing Cable Telephony in an region where it already provides cable TV services. The pilot program has 3,200 customers, of which, 2,000 are conventional systems customers of our existing Cable TV service. This service mix allows us an expressive, comparative, basis for service evaluation. The system was, purposely, not installed in a very new network or especially smooth performing network so that we could evaluate the effectiveness of the system using average, available, Hybrid Fibre Coaxial networks. To implement the project, we have had to adapt our distribution centres to operate with the V5.2 open protocol, so that the equipment of different manufacturers could be integrated. Since it is the first activation of the V5.2 protocol in Brazil, with different suppliers involved, CTBC Telecom has worked in partnership with Brazils CPqD Foundation for telecommunications research and development to establish conformity testing procedures needed for integrated national access. A few adaptations to the HFC network were also needed, since the availability required for telephone systems is considerably higher than for Cable TV transmission. To this end a network (cables, fibres and sources) monitoring system has been implemented. In general, the investment to rebuild the system has been small, since two-way connections were made available through the installation of cable modems in the HFC network.

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