 | Issue: | Latin America I 2000 |
| Article no.: | 4 | |
| Topic: | Broadband in My Home? What is it? | |
| Author: | Fredric J. Morris | |
| Title: | Editor-In-Chief | |
| Organisation: | Connect-World | |
| PDF size: | 24KB |
About author
Not available
Article abstract
Broadband is going home. Your home, everyones home. It will take several years, but it is coming. It will bring Instant response Internet. Like the automobile, the telephone and the personal computer it will have a profound, unpredictable, impact on all our lives.
Full Article
Broadband is a technical term that we all will hear much about in the near future. It refers to the transmission of a wide, or broad, range of frequencies at the same time. The amount of information that can be transmitted depends upon the frequencies available to carry it. As you broaden the range of frequencies used you increase the amount of information you can send; effectively, you increase the speed of transmission. A telephone signal is relatively narrow. At best, it transmits information slowly. New technologies, broadband technologies, increase the speed of transmission. High-speed data transmission is nothing new. Communications carriers and corporate networks, among others have been using high-speed communications for years. What is new is that high-speed communications will become the standard. Big businesses will have bigger and faster systems. High-speed, broadband, communications will also be the standard for many small businesses and the home. Within the next 5 to 10 years most businesses and homes in developed countries will have access to such services. Competitive forces and new technologies will also bring economically viable high-speed services to much of Latin America, including to its remote interior, within the same time frame. This may not sound like much, but peoples lives will change dramatically as more and more sign on to these systems. The widespread use of high-speed communications will be revolutionary. Internet, voice, text, images, video, data-instantly there, like electricity, when you turn on your computer. Low cost, flat rate, always on, instant communications to any place in the world, real-time shopping, remote education, medical services- even remote surgery, are just a few of the applications possible today. Broadband, high-speed, service, like all key technologies, will bring applications, and have an impact on society, we can scarcely imagine today. High capacity, wide bandwidth, broadband, links are the backbone of these high-speed systems. There are five contenders that are vying for the broadband market and a sixth, technically a bit more limited, that will play a role in the transition. The contenders are: cable TV, broadband by telephone or DSL (digital subscriber line), optical fibre, data transmission satellites and wireless broadband (LMDS). The sixth, almost high-speed, technology playing a role today is called ISDN (Integrated Services Digital Network). High-speed service is still in its infancy. There are very few fortunate enough to have one of these connections. In the United States, according to one study, there were only 1.6 million clients connected to the Web through cable TV companies and less than 230 thousand DSL connections at the end of 1999. In Latin America, except for corporate networks, isolated tests and some ISDN service, high-speed connections are still quite rare. Cable TV networks were planned to bring television signals to the home, not for the Internet. The original networks were laid out using coaxial cable. Over the years, the networks have been upgraded using fibre-optic cables to carry the signal from the point of origin to distribution points as close to the subscribers residence as possible. Coaxial cable carries the signal on the final leg to the subscriber. These hybrid fibre-coax (HFC) systems achieve substantial savings by using optical links only where they are most needed and making good use of the existing coaxial infrastructure. The resulting system, coupled to special cable modems, permit HFC networks to carry television signals, two-way Internet traffic and even telephone service. One television channel carries almost 30 Mbps. When used for two-way Internet traffic, the shared coaxial cable that distributes the signal to several houses, can deliver high-speed bursts of traffic to each user on the line. Practically speaking, users of a well-engineered HFC cable TV distribution system should be able to receive bursts of data at close to 10Mbs and return traffic at a lower rate. Cable TV systems are essentially giant party lines; everyone shares the same circuit. This is not a problem when each channel carries a television show; the signal strength might go down a little when everyone is watching the same channel, but this is easily compensated for. At peak hours, when a whole neighbourhood is sharing the same data channel to access the Internet, effective access can slow considerably. Everyone waits, even though the wait is measured in fractions of a second, when someone else transmits or receives and everyone, unless the signal is encrypted, can listen in. Once again, cable is a high-tech version of the old-fashioned telephone party line, anyone can listen in. The telephone companies look upon the communications market as their own. They are not about to hand it over to the cable companies. The telephone companies have some fibre networks and they are constantly building more. Most of their systems, though, connect to the final user through a twisted pair of wires that, in theory at least, should not be able to deliver more than about 33.6 kbps-kilobits per second, not the megabits delivered by cable TV. Digital trickery is used by recent modems to raise this limit, in one direction, to 56 kbps, but this is still far from adequate for many applications. The rate at which data can be transmitted through a copper wire depends upon the range of frequencies being transmitted and the noise level of the wire medium itself. Physical principles then determine the maximum transmission capacity. If you know the bandwidth and the ratio of the signal to the noise in the circuit you can calculate the maximum transmission capacity. Todays personal computer modems operate very close to this limit. A relatively new technology called digital subscriber line or DSL allows the speed limit to be side stepped under special circumstances. Transmission capacity is affected by attenuation of the signal, which reduces signal strength and limits the bandwidth, as it travels down the line. By limiting the length of the line to more or less 5 kilometres, and by using special signal coding, an intelligible signal can be transmitted at rates up to 1.5 megabits per second. Although this is not as fast as a cable signal it is not shared. It is private and, on a well-designed network, will not suffer speed losses as more users log on. There are several types of DSL. The version most indicated for home service is ADSL, the “A” stands for asymmetric; ADSL users receive data at rates of up to 1.5 mbps but sends data back at less than 0.5 Mbps. An ADSL modem converts the high frequency component of the signal and passes data to a computer. Telephone conversations can be carried on simultaneously. Data and voice are transmitted on the same line; a microfilter automatically shunts the lower frequency voice signals to the telephone. HDSL, “high-bit-rate” DSL uses a sophisticated multilevel coding scheme to achieve data rates of up to 8mbps on short, one and a half kilometer, line. SDSL “symmetric DSL”, aimed more at business users for high-speed two way traffic, maintains equal, symmetric, data rates in both directions. ADSL is, like electricity or water or gas, “always on.” You do not need to dial it up. When you turn on the computer, you are on the Internet. You stay on the Internet as long as the computer is on. Not all ADSL service is full speed. Telephone companies often offer lower speed versions (starting at 256 kbps and increasing in 64kbps increments) at lower prices. Although there are currently more cable TV connections to the Internet, the consensus is that ADSL, particularly the lower priced versions, will surpass cable connections within a year or two. ISDN is not quite broadband, but it occupies an important niche. Like DSL it also uses existing copper networks. Like DSL, the copper wiring limits service to within a 5-kilometer radius of the telephone companys exchange. ISDN service is offered in increments of 64kbps. Commonly, two circuits for a total of 128kbps are bundled together in a residential or small business package. The ISDN service is a good deal cheaper than DSL since it is routed through existing digital exchanges. Although it is slower than the true broadband technologies, it can be as much as 5 times faster than standard telephone line transmission. Normally, since it is a dial-up service, it is charged for on a per-minute basis, but flat rate service for local connections can be obtained from some operators. DSL is usually billed on a flat rate based on the velocity of the service contacted. ISDN users can speak on the telephone while using the ISDN data channel. All the services provided by a digital telephone exchange (call forwarding, standby, conference calling, caller ID, etc.) can be used, as well, through an ISDN telephone. Virtual switchboard service, similar to Centrex direct inward dialling, is available on ISDN lines from some operators. These systems permit outside phones to dial directly to a given extension or one extension to call another without the need to install a PABX on the premises. Optical fibre cables provide the fastest, broadest, data links available. Typically, point-to-point fibre connections can transmit signals of up to 100 million bits per second. This is many times faster than the best metallic cables, including coaxials, can manage. The cost of wiring a home for a direct optical connection is approximately US$1,500 including the electronics. There has been quite a reduction in the price over the years, but it is still much higher than the cost of metal cable. In order to reduce the cost, several compromise systems-fibre-to- the-node, fibre-to-the-cabinet, fibre-to- the-curb,-are sometimes used to reduce the cost. These systems bring fibre closer (30 to 1,000 metres) to the final destination and redistribute the signal using copper wire. It is cheaper, but it is also slower since the final copper connections slow the signal. All fibre circuits using passive optical circuits (PONs), and advances in equipment design are steadily reducing the price of all-optical networks. PONs networks consist of a fibre channel extending from the carriers exchange to an optical power splitter near to the final destination. The splitter, using optical devices, splits the signal into 16 or 32 equal signals. Individual fibres then carry the signal to an optical transceiver, which converts it into an electrical signal, in each house. By combining the signal for various households into a single cable and splitting it into individual circuits only for the last several metres, the cost of the network is reduced considerably. Fibre transmits more data more rapidly than any other system. When the price is low enough the demand will multiply. Service providers and manufacturers are now focusing on reducing the price of these networks. When they succeed, fibre might very well become the medium of choice crowding other systems out of much of the market. Hundreds of communications satellites are starting to crowd the sky. They are getting more powerful and more capable. New digital technologies are lowering costs, improving capacity and the security of the communications. These new systems operate at higher frequencies than those using older technologies. Using narrow beam radio signals they can be communicated with very small house-mounted antennas. The combined capacity of proposed systems is sufficient to handle, at least in theory, several times the worlds voice communications needs. There are two types of satellite systems: geostationary and low-earth-orbit (LEO). The geostationary satellites circle 36 thousand kilometres above the earth. Since they stay at a fixed point in relation to the earth below a stationary antenna can be used, but since they are so far up special circuits must be used to compensate for the delays in sending and receiving the signals. The LEO systems are much closer. They circle only 1,500 kilometres above the earth so little compensation is needed for signal delay. The antennas, however, need to be fairly sophisticated to track the rapidly moving satellites. Satellites are the second fastest broadband transmission system. Only direct to home fibre is faster. It is twice as fast as LMDS, 3 times or more faster than cable and more than 11 times faster than DSL. Satellites can reach just about any place on earth. You can have service as soon as the antenna is installed. No matter what the cost, and the performance, is the same. LMDS depends on direct line of sight transmission and works only over short distances. DSL and ISDN only work at distances of up to about 5 kilometres. Cable signals deteriorate as more subscribers are added to the line and fibre to many locations will be very expensive. The big problem with cable is the cost – US$4 to US$10 billion for a global system. Despite this several systems will be launched in the coming years and will bid, at least within specialized niches, for a large share of the broadband market. LMDS (local multipoint distribution service) is a new technology. It is a very high frequency wireless broadband system made possible by recent advances in digital signal processing technology and breakthroughs in manufacturing integrated circuit chips that operate efficiently in the millimeter wave bands in the 28 GHz (gigahertz) region of the spectrum. LMDS, due to high frequency transmission characteristics, is limited to line of sight operation in small, 2 to 5 kilometer, radius cells. These cells are not mobile; the antennas must remain fixed. The cell size is limited by an effect called rain fade. Raindrops scatter the signal and distort and absorb the signal in a way very much like what happens when food heats up by absorbing micro-waves in an oven. Any sort of matter, buildings, trees, even leaves, will cause the same effect. Conclusion LMDS transmits data at 155 Mbps and is quite effective for carrying internet connections, multiple voice channels, video conferencing, video streaming gaming applications and the like. Its main advantage is its flexibility and the speed with which it can be deployed to reach new regions. Since there is no wiring it is simple and relatively cheap to use reaching, regions where no wiring exists. LMDS channels can be used either by new operators to quickly roll out extensive high capacity networks or by existing operators to fill gaps in their network coverage.
