TELECOMMUNICATIONS TELECOMMUNICATIONS SYSTEM n A telecommunications system is

TELECOMMUNICATIONS

TELECOMMUNICATIONS SYSTEM n A telecommunications system is a collection of compatible hardware and software arranged to communicate information --text, graphics, images, voice, or video-- from one location to another.

COMPONENTS n Computers to process information, terminals and other input/output devices to send or receive data n Communications channels (telephone lines, fiber optic cables, coaxial cables, wireless transmission) to link sending and receiving devices in networks n Communications processors (modems, multiplexers, front-end processors) to provide support functions for data transmission n Communications software to control input and output activities and to manage other functions of the communications network

PRINCIPAL FUNCTIONS n Transmission of information n Establishing an interface between sender and n n n receiver Routing messages along the most efficient path Processing information to get the right message to the right receiver Checking and editing transmitted information for errors and formats Converting messages from the speeds and codes of one device to those of another Controlling the flow of information, routing messages and maintaining overall network structure

COMM. CHANNELS n Communication channels are means by which data are transmitted from one device in a network to another. n A channel can utilize different kinds of transmission media.

COMM. CHANNELS n Twisted Pair (Shielded Twisted Pair and Unshielded Twisted Pair) n Twisted wire consists of strands of copper wire twisted in pairs. Shielded twisted pair uses a special braided wire, which surrounds all the other wires, which helps to reduce unwanted interference. n The features of twisted pair cable are: n Low cost n Slow transmission (interference with high-speed transmission) n 10 MBps (baud rate)

COMM. CHANNELS n Coaxial Cable n Thickly insulated copper wire that can transmit a larger volume of data than twisted wire can. n The general features of coaxial cable are: n Up to 200 MBps n Fast n Interference free n Hard to wire n Does not support analog signals

COMM. CHANNELS n Fiber Optic n Consists of thousands of strands of clear glass fiber (human hair thick) which are bound into cables. Data are transformed into pulses of light, and sent by a laser device at a rate of 500 KBps to several billions per second. n High-speed [large bandwidth requirements like video, large database systems] long distances and interconnecting networks. n It costs more than either twisted pair or coax, and requires special connectors and jointing methods. n Durable, used for backbones [linking LAN’s together] or rings (100 Mbps)

COMM. CHANNELS n Wireless Transmission n Send signals through air or space n (cellular phone, microwave transmission-high frequency radio signal-25 to 30 miles apart not to be affected by earth curvature, communication satellitemicrowave signal bounced off satellite, etc. ).

COMM. DEVICES A modem is a device that translates digital signals into analog form (and vice versa) so that computers can transmit data over analog networks such as telephone and cable networks.

NETWORK TYPES n LAN (Local Area Network) n Small networks are often called Local Area Networks. A LAN is a network allowing easy access to other computers or peripherals. n The typical characteristics: physically limited (< 2 km) n high bandwidth (> 1 mbps) n inexpensive cable media (coax or twisted pair) n data and hardware sharing between users n

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NETWORK TYPES n Metropolitan Network n These are networks used inside cities and metropolitan areas. n Connections are done by fiber optic cabling for short distances or by modems. These also connect LANs together. n The use of these networks is to send data (files or faxes) from central office to distributors outside the city.

NETWORK TYPES n Wide Area Networks (WAN) n These networks can be regional, national or even international. They supply the organization with sound and video communications. n Communication is performed by satellites or microwaves as well as modems. For international networks communication requires some standards which are named as protocols. Internet is an example to WANs.

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NETWORK SEGMENT n A network segment is a length of cable that devices can be attached to, which has its own unique address and has a limit on its length and the number of devices, which can be attached to it.

NETWORK SEGMENT n Large networks are made by combining several individual network segments together, using appropriate devices like routers and/or bridges. Bridge is used to allow traffic from one network segment to the other. n Each network segment is considered unique and has its own limits of distance and the number of connections possible.

NETWORK SEGMENT n When network segments are combined into a single large network, paths exist between the individual network segments. These paths are called routes, and devices like routers and bridges keep tables, which define how to get to a particular computer on the network. n When a packet arrives, the router/bridge will look at the destination address of the packet, and determine which network segment the packet is to be transmitted on in order to get to its destination.

NETWORK TOPOLOGY n Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages. n The choice of topology is dependent upon: type and number of equipment being used n planned applications and rate of data transfers n required response times n cost n

BUS TOPOLOGY n All workstations connect to the same cable segment commonly used for implementing Ethernet at 10 mbps the cable is terminated at each end wiring is normally done point to point a faulty cable or workstation will take the entire LAN down two wire, generally coax. n Devices can be attached or detached from the network at any point without disturbing the rest of the network n Overall performance declines as more users and devices are added, because all message traffic must flow along the central bus n Today, the bus design is much less popular

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RING TOPOLOGY n Can be thought of as a bus network with the ends connected. The physical wiring can resemble a star pattern using a central device called Multistation Access Unit (MAU) wiring workstations into a logical ring. n One disadvantage of a ring network is that if a network device fails (such as a PC or a server), the devices downstream from the failed device cannot communicate with the network n Token ring protocol is used for controlling station access to the ring. A short message (called a token) is circulated around the ring, being passed from station to station (it originates from a controller or master station, which inserts it onto the ring.

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FDDI n Fiber Distributed Data Interface (FDDI) is based on two counter-rotating 100 -Mbit/sec token-passing rings. n The rings consist of point to point wiring between nodes, which repeat the data as it is received.

FDDI

STAR TOPOLOGY n All wiring is done from a central point (the server or hub) has the highest cable lengths of any topology. n Each workstation is wired in star fashion back to a concentrator-wiring centre (hub/switch). With 32/64. . ports. One of these ports is connected to a server, or the output of the hub can be connected to other hubs. n Disadvantage of the star design is that the entire network is dependent on the switch n However, in most large star networks, backup switches are available immediately in case of hardware failure

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Network Models n Routers differ from switches in that they connect networks n Gateway can connect to a larger, dissimilar network, such as the Internet n Proxy server provides Internet connectivity for internal LAN users 28

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Components of a Simple Computer Network Illustrated here is a very simple computer network, consisting of computers, a network operating system residing on a dedicated server computer, cabling (wiring) connecting the devices, network interface cards (NIC), switches, and a router.

Corporate Network Infrastructure Today’s corporate network infrastructure is a collection of many different networks from the public switched telephone network, to the Internet, to corporate local area networks linking workgroups, departments, or office floors.

Client/Server Architecture n Today’s interconnected world requires an information architecture that spans the entire enterprise n Whether you are dealing with a departmental network or a multinational corporation, as a systems analyst you will work with a distributed computing strategy called client/server architecture 32

Client/Server Architecture n Overview n Client/server architecture refers to systems that divide processing between one or more networked clients and a central server n The client submits a request for information form the server, which carries out the operation and responds to the client n Many early client/server systems did not produce expected savings 33

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Client/Server Architecture n Client/Server Tiers n Two-tier design; UI on client, data on server, application on both or on each n Three-tier design; UI on client, data on server, application on middle layer (application server), because it provides the application logic, or business logic n Three-tier designs also are called n-tier designs n The middle layer is more efficient and costeffective in large-scale systems 36

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