Broad Band Communication

The term Broad band refers to a telecommunications signal of greater bandwidth, in some sense, than another standard or usual signal (and the broader the band, the greater the capacity for traffic).

Broadband communications is usually considered to be any technology with transmission rates above the fastest speed available over a telephone line. Broadband transmission systems typically provide channels for data transmissions in different directions and by many different users. For example, the coaxial CATV system is a broadband system that delivers multiple television channels over the same cable. In addition, it can handle data transmissions (primarily Internet access for home users) in an entirely different frequency spectrum.

Refer to Network Core technologies for information about transmission systems such as SONET and DWDM that are used at the core of carrier and service provider networks.

Typical broadband communication systems include the following:

• ISDN (Integrated Services Digital Network): ISDN is implemented over existing copper telephone cables. The basic rate variety provides two channels of 64-Kbit/sec throughput that can be bonded to form a 128-Kbit/sec data channel. Primary rate ISDN provides additional bandwidth in increments of 64 Kbits/sec.
• ATM (Asynchronous Transfer mode): Another high-bandwidth service available from the carriers. The carriers use of ATM benefits everyone, but medium to large companies can install ATM equipment on-site to connect directly into carrier ATM networks and gain all the benefits of those systems. See the "ATM" heading for more information.
• Frame Relay: A data networking and voice service offered by the carriers that is widely available. Like ATM, frame relay is primarily used for corporate rather than home connections.
• Leased Lines and T Carriers: Leased T1 lines provide dedicated throughput of 1.544 Mbits/sec over two-pair twisted wire. Existing telephone cable is usually adequate. T3 provides approximately 45-Mbit/sec throughput. Fractional T1 can be leased in increments of 64 Kbits/sec. See "TDM Networks" for more details.
• DSL (Digital Subscriber Line): DSL is a whole family of high-bandwidth digital services that the telephone companies offer over copper telephone cable. Depending on the service, rates can reach into the multimegabit/sec rates.
• Cable (CATV) Data Networks: The cable TV system is a well-established broadband network that now makes its system available for data links and Internet access. Nearly 100 million homes in the U.S. have cable access, and it is estimated that 70 to 75 percent of those homes will be able to support Internet access in the year 2000.
• Wireless Communications: A variety of wireless broadband services are now available or under development, including satellite-based systems and terrestrial-based systems that are essentially fixed cellular systems. Broadband wireless uses microwave and millimeter wave technology to transmit signals from base stations to customers.

DSL, cable, and broadband wireless will largely solve the problem of providing high bandwidth to home users. This is the so-called "last mile," although last mile has traditionally referred to the copper local loop that connects homes to local telephone central offices. In this respect, CATV and broadband wireless have never had a last-mile problem. DSL solves the last-mile problem in the local loop.

Another aspect of most of these broadband technologies (although not directly related to the definition of broadband) is that they provide direct access to the Internet. There is no need to dial up and hope you get a connection. You are always connected, in the same way that your TV is always connected to the CATV network.

As bandwidth increases, customers will gain access to higher qualities of service for voice, video, and data using packet-based Internet technologies. Global Internet-based telephone calls and videoconferences will become more commonplace, as will distance learning and high-resolution imaging as applied in areas like telemedicine.

An interesting technology that can provide broadband service is HALO (High Altitude Long Operation), which is a scheme to put high-flying planes or balloons above major metropolitan areas. Angel technologies is promoting HALO in the form of a 28-GHz LMDS system that typically uses three planes as aerial base stations. Data rates are in the 10-Mbit/sec range. Skystation International uses balloons that provide 1-Mbit/sec to 12-Mbit/sec transfer rates. The systems connect with ISP and carriers so that users can access the global telecommunications infrastructure.

Line of sight Propagation:

Free Space Propagation:

In Line Of Sight, radio wave propagation takes place between two isolated isotropic antennas in an isotropic, homogeneous and lossless medium infinite in extent. In this case transmission takes place only along the direct ray path from the Transmitter to Receiver.

Satellite Communication:

In 1945, Arthur C. Clarke, a famous British science fiction writer noted that a satellite equatorial orbit with a radius of about 42,242 km would have an angular velocity that matched the earth's. Thus it would always remain above the same spot on the ground and could receive and relay signals from most of hemisphere. Three satellites spaced 120 degree apart could cover the whole world. Such orbit is geosynchronous orbit.

Optical Fiber Communication:  

Communication is defined as the transfer of information from one point to another. The function of optical sources is to produce light, which is coupled to the fiber. The intensity of the light output is varied according to the information to be transmitted. commonly used optical sources are light emitting diodes (LED's) and lasers. Communication using optical carrier wave guided along a glass fiber has a many attractive features, which makes optical fiber advantageous over other media particularly copper cable.