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1
Modern Telecommunication Networks
Syed A. Rizvi
2
Introduction
� Most modern telecommunication systems transfer information in digital format.
3
Introduction (Continued)
� The information may consist of voice, video, computer data, etc.
4
Essential Components
� Essential components of a modern communication system include:
1. Computers (for information processing)2. Input/output devices to send or receive data
� Input devices: keyboard, microphone, video camera, computer storage devices, etc.
� Output devices: display, printer, speakers, storage media
3. Communication channels: � telephone lines, coaxial cable, fiber optic cable, wireless
links etc.
5
Essential Comp….(Continued)
4. Supporting hardware to connect heterogeneous subnetworks:� Modems, multiplexers, routers, etc.
5. Communications software
6
Communication Channels
1. Twisted wires:� The oldest transmission medium� Low cost� Relatively slow for data transmission
2. Coaxial Cable:� Consists of thickly insulated copper wire� Can transmit larger amount of data� Faster than twisted wire
3. Fiber Optics Cables:1. Consists of thousands of strands of clear glass
fiber
7
Communication Channels (Continued)
2. Thickness of the glass fiber is as small as the thickness of a human hair
3. Data is transmitted into pulses of light4. More suitable for providing high-speed backbone
network� Advantages:
1. Lighter and more durable that coaxial cable and twisted wire
2. Can handle a very large volume of data
� Disadvantages:1. Difficult to work with2. Relatively expensive
8
Communication Channels (Continued)
1. Wireless links:� Data (information) is transmitted through
atmosphere via electro-magnetic waves
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Network Topologies
� Star Topology:
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Network Topologies: Star
� All computers in a star network are connected to each other through a host computer
� Host computer directs the incoming messages to the correct destination computer
� If the host computer goes down it affects the operation of whole star network
� Individual computer can be brought down for maintenance or removed without affecting the rest of the star network
11
Network Topologies (Continued)
� Bus network:
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Network Topologies: Bus
� All computers are connected through a common line (could be a twisted wire, coaxial cable, fiber optics cable etc.)
� Each message is broadcasted in both directions to the entire network
� If a computer goes down, it does not affect the rest of the network
� Bus network handles one message at a time� If two or more computers send messages
simultaneously a collision occurs, the messages must be re-sent
13
Network Topologies (Continued)
� Token Ring Network:
14
Network Topologies: Token Ring
� In a ring network, computers are connected via a closed loop wired connection
� Data is transmitted in one direction � A token is passed through the ring and any
computer in need of transmitting the data holds the token and starts transmitting the message
� The computer with the delivery address receives the data
� When the message arrives at the source computer it signals the completion of the transmission
15
Network Topologies: Token Ring
� The computer holding the token then passes the token to the next computer
� If the next computer needs to send the data it will hold the token and start transmitting the message; otherwise, it will pass the token to the next computer
16
Local Area Network (LAN)
� Local area network covers a limited area such as a building or a few buildings in a close proximity
17
LAN (Continued)
� LAN generally use Bus or Ring topology� Usually connects computer and related equipment
with in 2000 feet radius� Often used to connect PCs/workstation to shared
printers and file-servers etc.� A special computer known as network gateway
connects the LAN to other networks� Both wired and wireless LAN technologies are
available � Wide area networks (WAN) span a large
geographical area and contain thousands of LANs and other heterogeneous networks in an entire continents
18
Enterprise Networking
� An enterprise network connects PCs, workstations, NCs, LANs, and other organization-wide computing resources together as well as to Internet