With cable modems initially reaching speeds of around 10 Mbit/sec (MCNS standard handled by the U.S.) and 56 Mbit/s (DVB/DAVIC standard handled by Europe), subscribers are promised a wide range of services such as pay-per-view, video-per-demand (VOD), interactivity, telephony, Internet access, audio on demand (AOD) and telemetry, among others.
In addition to new customer needs, which now include a combination of recreation and information, other elements of great importance for the development between cable TV networks and global interactive communications systems are:
- changes in the legal environment, such as liberalization;
- new technologies based on fibre optics and digital transmission, and
- the convergence between data processing and telecommunications.
One of the most promising new interactive services is high-speed Internet. The home PC has become the norm and as global network clients demand more speed, the cable lends itself to becoming the access network of choice.
However, to become a fully interactive medium, it is necessary to install a return channel in the physical transmission layer, accompanied by a control protocol. The real challenge for transmission and logical layers is the installation of a return channel that goes from the end user to the service provider.
Optical transmission
Cable networks tend to vary in size, capacity (with frequency limits from 300 MHz to 860 MHz), technology (architecture, amount of optical fiber used), and type of owner (private, public, community, or government).
For several decades, analog cable TV technology used coaxial cable and cascading broadband amplifiers with a branched structure. Reliability, image quality and transmission capacity were limited due to the large number of cascade amplifiers needed.
The situation changed completely with the advent of optical transmission. Monomodal fibers and high linearity distributed feedback (DFB) lasers make it possible to employ optical transmission in the same broadband, multichannel, and frequency multiplex signals as in coaxial cable signals, and the main advantage of optical fiber is that it requires very low attenuation.
Therefore, the strength of optical fiber lies in the low degree of loss in signal transport between two points very distant from each other, while that of coaxial cable is still point-multipoint distribution.
Hybrid networks
Modern cable networks combine the advantages of both technologies in hybrid fiber/coaxial (HFC) network architecture. Video compression and efficient broadband modulation methods increase program transport capacity over cable networks by a factor of eight or more times.
Another aspect is the provision of return data capacity, which depends on the type of interactive services, the acceptance of new services by subscribers and competition, among other factors.
Most of them are not very well known, but they are known to directly influence matters on which immediate decisions must be made, such as the range of return frequencies to be provided in the coaxial cable and the size of the cells (i.e. the number of subscribers sharing a coaxial distribution unit).
Likewise, the introduction of the return channel must be carried out with the minimum possible changes in the network. Several international organizations are engaged in standardization to achieve interoperability of equipment from different manufacturers.
Shlomo Rakib of Terayon Communications Services, USA, says: "Today's cable operators face the challenge of providing data to a broad spectrum of users with different bandwidth and quality of service requirements. The characteristics of a shared cable network demand systems that allow operators to provide and allocate bandwidth to multiple levels of users. Only then will operators be able to accommodate bandwidth to the needs of residential and commercial users, and build a service model that optimizes profits."
Operator Solutions
To support this model, the cable operator must install a cable modem system that provides adequate bandwidth capacity in both directions and is able to provide the bandwidth to support a wide range of application needs for the user.
In the nineties, cable TV networks usually have a connection to the system, located near the main entrance or in the living room of the residence. One way to connect the wired network directly to the home is through a wireless network in the same house, which saves the costs associated with installing the wired connections inside the home.
The wireless solution is interesting from the point of view of communication with the PC, whose modem contains a high-speed coaxial impeller connector and an antenna for wireless communication.
If the coaxial cable is connected, the communication retains its full functionality, that is, its total speed. if you do not connect the communication retains its full functionality even though the downstream speed is reduced to the values that correspond to the speed Upstream.
In the last case, the PC acquires 100% mobility. With the increasing penetration of laptop and palmtop, mobility is becoming more and more important.
Since both standardized and open networking solutions are recommended, there are not as many wireless system options. In Europe, only DECT is presented as a possibility with which a solid wireless solution has been offered for telecommunications (circuit switching services) and data communication (packet switching services).
More than 40 million cable TV subscribers are connected to European cable TV networks. This means that more than 40 million homes are already part of high-capacity broadband communication systems. This number is also growing in the U.S., and in the rest of the world it is not so far behind.
