SIGNALS: DIGITAL VS ANALOG
- Analog signal is represented by a continiuous waveform that passes thought acommunication medium an has been used for voice communication.
- A digital signal is a discrete,binary waveform, rather than a continuos waveform.
- Digital signals communicate information as strings of two discrete states: one bit and zerobits, which are represented as on–off electrical pulses.
- Called a modem to translate digital signals into analog form.
FIGURE 7.1 Functions of the modem
- A modem is a device that translates digital signals from a computer into analog form so that they can be transmitted over analog telephone lines. The modem also translates analog signals back into digital form for the receiving computer.
Modem
Local area network (LAN)
Type of
networks
LOCAL AREA NETWORK(LAN)
- Designed to connect personal computers and other digital devices within a halfmile or 500-metre radius.
- Connect a few computers in a small office, all the computers in one building, or all the computers in several buildings in close proximity Windows, Linux, and Novell.
- three major LAN topologies:
- Star topology :all devices on the network connect to a single hub organized into a hierarchy.
- Bus topology, one station transmits signals, which travel in both directions along a single transmission segment. All machines on the network receive the same signals, and software installed on the client’s enables each client to listen for messages addressed.
- Ring topology connects network components in a closed loop.Messages pass from computer to computer in only one direction.
CAMPUS AREA NETWORK(CAN)
- Up to 1,000 meters(a mile);a college campus or corporate facility.
- CAN is a network of multiple interconnected local area networks (LAN) in a limited geographical area. A CAN is smaller than a wide area network (WAN) or metropolitan area network (MAN).
- CAN benefits are as follows:
- Cost-effective
- Wireless, versus cable
- Multidepartmental network access..
- Single shared data transfer rate (DTR)
Metropolitan
area network(MAN)
- Span broad geographical distances—entire regions, states, continents, or the entire glob.
- Computers connect through public networks such as the telephone system or private cable systems, or through leased lines or satellites.
WIDE
AREA NETWORK(MAN)
- A network that spans a metropolitan area,usually a city and its major suburbsIts geographic scope falls between a WAN and a LAN
FIGURES 7.1 NETWORK TOPOLOGIES
- Wide range of speeds is possible for any given medium depending on the software and hardware configuration
TRASMISSION MEDIA AND TRANSMISSION SPEED
- Networks use different kinds of physical tranmission media:
- Twisted Wire consists of strands of copper wire twisted in pairs and is an older type of transmission medium.
- The telephone systems in buildings had twisted wires installed for analog communication.
- Used LANs, such as CAT5
Coaxial Cable
- Coaxial cable, similar to that used for cable television, consists of thickly insulated copper wire.
- Transmit a larger volume of data than twisted wire.
Fibre Optics and Optical Networks
- Fibre optic cable consists of bound strands of clearglass fibre, each the thickness of a human hair.
- Data are transformed into pulses of light,which are sent through the fibre optic cable by a laser device.
Wireless Transmission Media
- Wireless transmission is based on radio signals of various frequenciessed to handles the major traffic.
- Microwave systems ;follow a straight line and do not bend with the curvature of the earth.
- Such as Communication satellites are typically used for transmission in large.
Transmission Speed
- The total amount of digital information that can be transmitted through any telecommunications medium is measured in bits per second.
- Hertz frequencies that can be accommodated on a particular telecommunications channel is called its bandwidth
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