DATA COMMUNICATION HARDWARE AND NETWORKING

1. DATA COMMUNICATION HARDWARE AND NETWORKING Data can travel within the computer distances from a few thousandths of a centimeter, as within a single IC, to 10s of centimeters along the main circuit board. Over small distances, digital data can be transferred directly as two-level electrical signals over simple copper conductors Frequently, however, data must be sent beyond the local circuitry that constitutes a computer. In many cases, the distances involved may be enormous. Unfortunately, as the distance between the source of a message and its destination increases, accurate transmission becomes increasingly difficult. This results from the electrical distortion of signals traveling through long conductors, and from noise added to the signal as it propagates through a transmission medium.

2. DATA TRANSFER IN DIGITAL CIRCUITS TRANSFER OVER MEDIUM DISTANCES

3. DATA COMMUNICATIONS concerns the transmission of digital messages to devices external to the message source. "External" devices are generally thought of as being independently powered circuitry that exists beyond the chassis of a computer or other digital message source (NETWORKS). As a rule, the maximum permissible transmission rate of a message is directly proportional to signal power, and inversely proportional to channel noise. It is the aim of any communications system to provide the highest possible transmission rate at the lowest possible power and with the least possible noise.

4. COMMUNICATIONS CHANNEL is the medium through which digital information must pass to get from one location to another. It may be defined by a physical wire that connects communicating devices, or by a radio, laser, or other radiated energy source that has no obvious physical presence. Information sent through a communications channel has a source from which the information originates, and a destination to which the information is delivered. Although information originates from a single source, there may be more than one destination, depending upon how many receive stations are linked to the channel and how much energy the transmitted signal possesses. In a digital communications channel, the information is represented by individual data bits

5. Data can be transmitted between 2 points in 2 ways: SERIAL PARALLEL In Serial Transmission, data is sent bit by bit. In Parallel Transmission, all bits are sent at once, and each bit is sent on a separate wire 10010101 10010101 sender media receiver bit 0 bit 0 bit 1 bit 1 bit 2 bit 2 bit 3 bit 3 bit 4 bit 4 bit 5 bit 5 bit 6 bit 6 bit 7 bit 7 sender media receiver

6. Any communications channel has a direction associated with it: The message source is the transmitter, and the destination is the receiver. A channel whose direction of transmission is unchanging is referred to as a simplex channel. For example, a radio station is a simplex channel because it always transmits the signal to its listeners and never allows them to transmit back.

7. A half-duplex channel is a single physical channel in which the direction may be reversed. Messages may flow in two directions, but never at the same time, in a half-duplex system. In a telephone call, one party speaks while the other listens. After a pause, the other party speaks and the first party listens. Speaking simultaneously results in garbled sound that cannot be understood.A full-duplex channel allows simultaneous message exchange in both directions. It really consists of two simplex channels, a forward channel and a reverse channel, linking the same points.

9. TRANSMISSION MEDIA A variety of communications channels, some with wires, some without, carry digital signals between computers Each channel is rated by its CHANNEL CAPACITY, or BANDWIDTH. The channel capacity is the number of bits a channel can transmit per second (baudrate). TWISTED-PAIR WIRE POTS (Plain Old Telephone Services): regular analog phone line – permits voice data transmission traditional lines permit data transmission rates of 56 K bps ISDN (Integrated Services Digital Network): terminates at an ISDN modem. permits faster data transmission, about 128 K bps for BRI. (2 M bps for PRI) DSL (Digital Subscriber Line): much faster transmission rate achieved by new technology about 1.5 – 9 M bps requires special modem

11. COAXIAL CABLE (otherwise known as the cable TV): Contains electrical cable (usually copper wire) Permits high-speed data transmission with minimum signal distortion Laid along the ocean floor for intercontinental data transmission Has a high capacity channel – can carry digital data of up to 10 M bps WIRELESS COMMUNICATION: Data can also be transmitted using microwave signals or radio signals. Signal travels in a straight line from source to destination – transceivers are placed on top Of high mountains… Or geosynchronous orbits… Internet access via satellite is available at speeds up to 48 M bps.

12. WIRELESS COMMUNICATION THROUGH MICROWAVES

13. FIBER OPTIC CABLES: Carries data as laser-generated pulses of light. (LASER: Light Amplification by Stimulated Emission of Radiation) Carry data more inexpensively and much more quickly than copper wires – PLUS provides data security – harder to intercept a beam of light!!!

14. COMMON CARRIERS A PRIVATE LINE, or LEASED LINE is a dedicated data communications channel between any two points in a computer network. The charge for a private line is based on channel capacity (bps) and distance. A SWITCHED LINE, or DIAL-UP LINE, is available on a time- and distance charge, like a phone call.

15. DATA COMMUNICATIONS HARDWARE Data communications, or telecommunications, is the electronic collection and distribution of information between two points. Data communications hardware is used to transmit digital information between terminals and computers, or between computers and other computers. Host computer Concentrators Front-end processor Hubs Multiplexer Network Interface Cards Router Modem

16. A SIMPLIFIED COMMUNICATION MODEL

17. THE MODEM • If your computer is not connected to a LAN, it is still possible to establish a link with other computers if • You have access to a telephone line • Your PC is equipped with a modem NETWORK INTERFACE CARDS An add-on board that enables and controls the exchange of data within a LAN. FRONT-END PROCESSOR Establishes the link between the source and the destination in a process known as the hand-shaking. It is a computer-based device that relieves the host computer of a variety of communications-related processing duties. This leaves the host free to concentrate on overall systems control and execution of applications software.

18. MULTIPLEXING AND THE MULTIPLEXER • The concept of multiplexingis fundamental to computer networks. Multiplexingallows several transmitting sources to share a larger transmission capacity, thereby making more efficient use of communication lines. • A multiplexer (MUX) is a device that is used to transmit multiple connections over a single physical link, thereby minimizing the no. of transmission lines required. • Multiplexers operate at higher bit rates than individual terminal rates.

19. ROUTER Networks use a variety of communications protocols and operating systems Therefore, incompatible networks cannot directly “talk” to each other Routers are the primary hardware/software technology used to connect incompatible networks. They carry out the necessary protocol conversions. BACKBONE Interconnections of computer networks are done over a backbone, the system of routers and the transmission media (cables, wires, links).