Communication channels are classified as analog or digital. Bandwidth refers to the data throughput capacity of any communication channel. As bandwidth increases, more information per unit of time can pass through the channel. A simple analogy compares a communication channel to a water pipe. The larger the pipe, the more water can flow through it at a faster rate, just as a high capacity communication channel allows more data to flow at a higher rate than is possible with a lower capacity channel.
In addition to describing the capacity of a communication channel, the term "bandwidth" is frequently, and somewhat confusingly, applied to information transport requirements. For example, it might be specified that a broadcast signal requires a channel with a bandwidth of six MHz to transmit a television signal without loss or distortion. Bandwidth limitations arise from the physical properties of matter and energy. Every physical transmission medium has a finite bandwidth. The bandwidth of any given medium determines its communications efficiency for voice, data, graphics, or full motion video.
Widespread use of the Internet has increased public awareness of telecommunications bandwidth because both consumers and service providers are interested in optimizing the speed of Internet access and the speed with which web pages appear on computer screens.
Natural signals such as those associated with voice, music, or vision, are analog in nature. Analog signals are represented by a sine wave , and analog channel capacities are measured in hertz (Hz) or cycles per second. Analog signals vary in amplitude (signal strength) or frequency (signal pitch or tone). Analog bandwidth is calculated by finding the difference between the minimum and maximum amplitudes or frequencies found on the particular communication channel.
For example, the bandwidth allocation of a telephone voice grade channel, which is classified as narrowband , is normally about 4,000 Hz, but the voice channel actually uses frequencies from 300 to 3,400 Hz, yielding a bandwidth that is 3,100 Hz wide. The additional space or guardbands on each side of the voice channel serve to prevent signal overlap with adjacent channels and are also used for transmitting call management information.
Signals in computing environments are digital. Digital signals are described as discrete, or discontinuous, because they are transmitted in small, separate units called bits. Digital channel capacities are measured in either bits per second (bps) or signal changes per second, which is known as the baud rate. Although these terms are frequently used interchangeably, bits per second and baud rate are technically not the same. Baud rate is an actual measure of the number of signal changes that occur per second rather than the number of bits actually transmitted per second. Prefixes used in the measurement of data transmission speeds include kilo (thousands), mega (millions), giga (thousands of millions), and tera (thousands of giga). To describe digital transmission capabilities in bits per second, notations such as Kbps, Mbps, Gbps, and Tbps are common.
The telephone system has been in a gradual transition from an analog to a digital network. In order to transmit a digital signal over a conventional analog telephone line, a modem is needed to modulate the signal of the sender and demodulate the signal for the receiver. The term modem is an abbreviation of modulate-demodulate. Although the core capacity of the telephone network has experienced an explosion in available bandwidth, local access to homes and businesses, referred to as the local loop in the telephone network, frequently is limited to analog modem connections. Digital transmission is popular because it is a reliable, high-speed service that eliminates the need for modems.
Financial and other business activities, software downloads, video conferencing, and distance education have created a need for greater bandwidth. The term broadband is used to refer to hardware and media that can support a wide bandwidth. Coaxial cable and microwave transmission are classified as broadband. Coaxial cable, used for cable television, has a bandwidth of 500,000,000 Hz, or 500 megahertz, and microwave transmission has a bandwidth of 10,000 Hz.
The capacity potential of broadband devices is considerably greater than that of narrowband technology, resulting in greater data transmission speeds and faster download speeds, which are important to Internet users. Data transmission speeds range from a low of 14,400 bps on a low speed modem to more than ten gigabits per second on a fiber optic cable. On the assumption that 50,000 bits represents a page of data, it takes 3.5 seconds to transmit the page at 14,400 bps, but only 8/10 of a second at 64,000 bps. If a page of graphics contains one million bits per page, it takes more than a minute to transmit the page at 14,400 bps, compared to 16 seconds at 64 Kbps. Full motion video requires an enormous bandwidth of 12 Mbps.
Upload versus Download Bandwidth
Among Internet Service Providers (ISPs) and broadband cable or satellite links, there is considerable difference in upstream, or upload, bandwidth and downstream, or download, bandwidth. Upstream transmission occurs when one sends information to an ISP whereas downstream transmission occurs when information is received from an ISP. For example, a broadband cable modem connection might transmit upstream at one Mbps and downstream at ten Mbps.
Typical media used to connect to the Internet, along with upstream and downstream bandwidths include: T3 leased lines, T1 leased lines, cable modems, asymmetric digital subscribe lines (ADSLs), integrated services digital networks (ISDNs), and dial-up modems. As noted in Gary P. Schneider and James T. Perry's book Electronic Commerce, T3 leased lines provide the fastest speeds (44,700 kbps for both upstream and downstream speeds) while the rates for T1 leased lines are 1,544 kbps, ISDNs are 128 kbps, and dial-up modems are 56 kbps. ADSL upstream and downstream speeds are 640 and 9,000 kbps, respectively, while cable modem speeds are 768 kbps upstream and 10,000 kbps downstream.
Each of the connections has advantages and disadvantages. As the speed of the medium increases in the broadband media beginning with T1 lines, costs increase substantially. Although classified as broadband, cable modems are considered optimal in price and performance for the home user.
History of Bandwidth Research
Researchers have studied the effects of bandwidth on network traffic since the 1920s. Research objectives have always focused on the development of encoding techniques and technology enhancements that allow more bits to be transmitted per unit of time. In 1933 Harry Nyquist discovered a fundamental relationship between the bandwidth of a transmission system and the maximum number of bits per second that can be transmitted over that system. The Nyquist Intersymbol Interference Theorem allows one to calculate a theoretical maximum rate at which data can be sent. Nyquist's Theorem encourages data communications professionals to devise innovative coding schemes that will facilitate the maximum transmission of data per unit of time.
In 1948, noting that Nyquist's Theorem establishes an absolute maximum not achievable in practice, Claude Shannon of Bell Labs provided refinements to the theorem to account for the average amount of inherent noise or interference found on the transmission line. Shannon's Theorem can be summarized as saying that the laws of physics limit the speed of data transmission in a system and cannot be overcome by innovative coding schemes.
see also Fiber Optics; Networks; Shannon, Claude E.; Telecommunications.
Thomas A. Pollack
Comer, Douglas E. Computer Networks and Internets. Upper Saddle River, NJ: Prentice Hall, 2001.
Rosenbush, Steve. "Broadband: 'What Happened?'" Business Week, June 11, 2001, pp. 38-41.
Schneider, Gary P., and James T. Perry. Electronic Commerce. Canada: Course Technology, 2001.
Bandwidth deals with how information passes through electronic systems. Since today's business world relies heavily on online communication, Internet research, and intranet resources, bandwidth is a primary concern in emerging technologies. When technicians speak of gaining or needing bandwidth, they are referring to the ability to transmit more information through the online connections. Many measurements involving bandwidth are also important to companies, such as how much data is transmitted in a continuous flow and how much data can be transmitted over a particular time.
FACTORS AFFECTING BANDWIDTH
Bandwidth can be used in a very broad definition; in this manner, it often refers to any need for more time, information, and space. In a connotative sense, bandwidth can mean the number of employees in a given department or the time constraints on a particular project. The narrow meaning of the word bandwidth is the electrical capacity, either analog or digital. In analog channels the rate is defined in hertz, the difference between higher and lower frequencies. In digital channels, the rate is defined by bits per second.
Company bandwidth, no matter how it is received, can be limited by several different factors, most notably the relationship between what online applications the company is using and the services and technology cable and DSL (digital subscriber line) providers offer. There are several important terms used in describing bandwidth space and a company's use of it:
- Bottleneck link bandwidth. This is the maximum rate data can travel in a given online system, from the source to the end receiver. This definition assumes that the data is traveling on the slowest possible path between its destinations.
- Surplus available bandwidth. This is the amount of bandwidth left over after the company has used all of its available bandwidth in the bottleneck link scenario. Businesses often deal with this concept since they have multiple applications and have usually purchased a large amount of bandwidth from their provider.
- Fair-share available bandwidth. A company rarely reaches and surpasses this level of use, unless it is pursuing aggressive or inappropriate bandwidth usage that drowns out other users and creates a state of congestion along the provider's line. Fair-share bandwidth is the maximum amount any business should plan on using, an amount that neither interferes with online communication traffic nor consumes too much space for company usage.
- Protocol-dependent available bandwidth. Based on what applications it is using, this is the amount of bandwidth a company should expect to take. This number may be produced by an agreement with the server or as a natural result of business expectations. The protocol-dependent bandwidth is how much bandwidth the company needs to run, and it lies somewhere between surplus bandwidth and fair-share bandwidth.
GENERAL GUIDELINES ABOUT BANDWIDTH USAGE
Despite the increasing availability of high-speed Internet connections and new ways of transferring data, bandwidth consumption remains a concern for many Internet providers, and businesses should be careful when purchasing and using their bandwidth so that they are not subject to penalties or sudden price adjustments. Consumption should be carefully monitored; this can be done with a simple program that can be bought or downloaded for free from certain Web sites. Bandwidth use should also be plotted over time so that companies can see if there are any sudden changes and where those changes may have come from. It is possible that employees, attracted by the high-speed connection offered by their company, will use company bandwidth for personal downloads, which can use a large amount of available space. There are bandwidth-management systems that can be put into place to automatically regulate Internet usage and help undo such problems.
Some business analysts have concerns, which are summed up by Tim Wu in a 2008 article, “OPEC 2.0.” In this piece, Wu theorizes that bandwidth may become another scarce, necessary commodity, in the same way that oil is today. Wu points to the control of bandwidth in the hands of only a few companies, and the growing need for bandwidth to run information-driven societies, as signs of this trend. However, current bandwidth rates are neither high enough or consequential enough to prove this theory, and although most businesses depend on online interaction of some type, restrictions regarding the flow of information have not yet hampered overall productivity.
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Bandwidth is the amount of data that moves along transmission lines or circuits at a given speed. For example, the time it takes a personal computer to load a word-processing program is dependent upon bandwidth, as is the load time for a World Wide Web page. Transmission speed is expressed either in bits-per-second (bps) for digital devices such as modems, or cycles-per-second, more commonly known as hertz (Hz), for analog devices such as microprocessors.
When bandwidth is inadequate for the function being performed, the slowdown that occurs is called a bottleneck. Bottlenecks can reduce either the transmission speed of data between components of a computer or within both local area and wide area networks. To circumvent this problem, personal computer manufacturers have developed machines with much faster busses—the circuits that actually carry data throughout a computer—such as the 40 mHz VL-bus and the 66 mHz AGP. Similarly, increased Internet traffic, and the more sophisticated graphical applications available on the World Wide Web, have prompted networking technology firms to develop devices like Gigabit Ethernet, Fast Token Rings, and T1 lines as a means of offering increased bandwidth rates to businesses and other institutions, as well as to individuals.
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SEE ALSO: Bandwidth Management; Connectivity, Internet; Microprocessor
1. of a transmission channel. A measure of the information-carrying capacity of the channel, usually the range of frequencies passed by the channel. This will often consist of a single passband, but may instead consist of several distinct (nonoverlapping) passbands. Each passband contributes to the bandwidth of the channel a quantity equal to the difference between its upper and lower frequency limits; the sum of all such differences plus necessary guard-bonds gives the total bandwidth required.
In these cases bandwidth is measured in frequency units, i.e. hertz (Hz). If the bandwidth is considered in a transform domain other than frequency (such as sequency) then it is measured in the appropriate units. In defining channels and filters in the frequency domain, bandwidth, unless otherwise defined, is assumed to be the frequency range between the points at which the frequency response is 3 decibels lower than the passband frequency and is sometimes known as the half-power bandwidth.
See also band-limited channel, channel coding theorem (for Shannon–Hartley law), Nyquist's criterion.
2.. A measure of the rate of transfer of digital information, usually expressed in bits or bytes per second.
3. See band matrix.
band·width / ˈbandˌwid[unvoicedth]/ • n. Electr. a range of frequencies within a given band, in particular: ∎ the range of frequencies used for transmitting a signal. ∎ the transmission capacity of a computer network or other telecommunication system. ∎ fig. the breadth of a person's interests or mental capacity.