Introduction to InformationSystems

Lecture 06Telecommunications and NetworksBusiness Value of Networks

Jaeki Song

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Metcalfe’s Law• The usefulness of a network equals the square of the

number of users• Number of possible connections on a network is N * (N-

1)• Where N = number of nodes (points of connections

on the network)• Example, if there are 10 computers on a network,

there are 10 * 9 = 90 possible connections• On a small network, a change in technology affects

technology only• On a large network like the Internet, a change in

technology affects social, political and economic systems

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Telecommunications• Telecommunications

• Exchange of information in any form (voice, data, text, images, audio, video) over networks

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Open Systems• Information systems that use common standards for

hardware, software, applications and networks

• Internet networking technologies are a common standard for open systems

• Connectivity:

• Ability of networked computers to easily access and communicate with each other and share information

• Interoperability:

• The ability of an open system to enable end user applications to be accomplished using different varieties of computer systems, software packages, and databases provided by a variety of interconnected networks

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Business Value of Telecommunication Networks

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Internet Revolution

• Key Facts• Over 46 million servers (2004)• 710 – 945 million users (2004)• No central computer system, No governing body, No

one owns it

• Internet Service Provider (ISP)• A company that specializes in providing easy access

to the Internet• For a monthly fee, you get software, user name,

password and access

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Business value of the Internet

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An Intranet

• A network inside an organization• That uses Internet technologies (such as Web

browsers and servers, TCP/IP protocols, HTML, etc.)• To provide an Internet-like environment within the

organization• For information sharing, communications,

collaboration and support of business processes• Protected by security measures • Can be accessed by authorized users through the

Internet

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Extranet

• Network links that use Internet technologies• To connect the Intranet of a business• With the Intranets of its customers, suppliers or other

business partners

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Telecommunications network

• Any arrangement where a sender transmits a message to a receiver over a channel consisting of some type of medium

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Telecommunications network model

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Types of Telecommunication Networks

• Wide Area Network (WAN)• Telecommunications network that covers a large

geographic area

• Local Area Network (LAN)• Connect computers within a limited physical area

such as an office, classroom, or building

• Virtual Private Network (VPN)• A secure network that uses the Internet as its

backbone but relies on firewalls, encryption and other security Source: Courtesy of Cisco Systems Inc.

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Types of Telecommunication Networks

• Client and Server Networks• Clients: End user personal computers or networked

computers• Servers: manage networks

• Network Computing• Networks are the central computing resource of the

organization• Thin clients: network computers and other clients

provide a browser-based user interface

• Peer-to-Peer Network• Networks that connect from one PC to another PC• Common use is the downloading and trading of files

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Telecommunications Media

• Wired• Twisted-pair wire:

• Ordinary telephone wire• Copper wire twisted into pairs

• Coaxial cable:• Sturdy copper or aluminum wire wrapped with spacers to insulate

and protect it

• Fiber-optic cable:• One or more hair-thin filaments of glass fiber wrapped in a

protective jacket

• Wireless

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Problem of “The Last Mile”

• Network providers use fiber optic to provide backbone

• But houses are connected to the backbone via twisted-pair

• Cannot get the benefit of the faster, better technology

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Wireless Technologies

• Terrestrial microwave• Earthbound microwave systems that transmit high-

speed radio signals in a line-of-sight path• Between relay systems spaced approximately 30-

miles apart

• Communications satellites• Satellite serves as relay stations for communications

signals• Uses microwave radio signals

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Wireless Technologies

• Cellular and PCS telephone and pager systems• Divide the geographic area into small areas or cells• Each cell has transmitter or radio relay antenna to

send message from one cell to another

• Wireless LANs• Radio signals within an office or building• Connect PCs to networks

• Bluetooth• Short-range wireless technology• To connect PC to peripherals such as printer

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Telecommunications Processors

• Modems• Convert digital signals from a computer into

• Analog frequencies that can be transmitted over ordinary telephone lines

• Internetwork Processors• Switch – makes connections between

telecommunications circuits in a network

• Router – intelligent communications processor that interconnects networks based on different protocols

• Hub – a port switching communications processor

• Gateway – connects networks using different communications architectures

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Network Architectures & Protocols

• Protocol: standard set of rules and procedures for the control of communications in a network

• Network Architecture: • Master plan of standard protocols, hardware, software

and interfaces between end users and computer systems

• Goal of promoting an open, simple, flexible, and efficient telecommunications environment

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OSI & TCP/IP Models

• Open Systems Interconnection (OSI) Model• A seven-layer model that serves as a standard model

for network architectures• Model for how messages should be transmitted

between two points in a network• Each layer adds functions

• Transmission Control Protocol / Internet Protocol (TCP/IP)• A five layer telecommunications protocol used by the

Internet

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OSI & TCP/IP Models

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Internet Telephony

• Using an Internet connection to pass voice data using IP

• Voice over IP (VoIP)

• Skips standard long-distance phone charges

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Switching Alternatives

• Circuit Switching • Switch opens a circuit to establish a link between a

sender and receiver• it remains open until the communication session is

completed

• Packet Switching• Break messages into groups called packets• Transmit packets separately