IST 1010 Introduction to information technology

9th Feb 2011

• Agenda– Overview: communication, computer networks– Telecommunication: Media, etc– Types of networks: PAN, LAN, MAN, WAN– Network topologies– Carriers and services– Distributed, centralized,

Communications

• Communications– The message (data and information) is

communicated via the signal– The transmission medium “carries” the signal

Sender ReceiverSignal

Transmissionmedium

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Computer Networks• A computer network is a system for communicating

between two or more computers and associated devices. It is an interconnection of computers for the purposes of sharing information and resources.

• A popular example of a computer network is the internet, which allows millions of users to share information

• Computer networks can be classified according to their size:– Personal area network (PAN)– Local area network (LAN)– Metropolitan area network (MAN)– Wide area network (WAN)

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Router

An example of a network

Internet

Segment Node

Hub

Hub

Bridge

Telecommunications

• Telecommunications– The electronic transmission of signals for communications,

including such means as:• Telephone• Radio• Television

• Telecommunication medium• Anything that carries an electronic signal and interfaces between a

sending device and a receiving device

Communications and Telecommunications

• In human speech, the sender transmits a signal through the transmission medium of the air

• In telecommunications, the sender transmits a signal through the transmission medium of a cable

Schematic

Data Communications

• Data communications– A specialized subset of telecommunications that

refers to the electronic collection, processing, and distribution of data -- typically between computer system hardware devices

Elements of a Telecommunications System

• Telecommunication devices– Relay signals between computer systems and

transmission media

Schematic

Computer Network

• Computer network…– The communications media, devices, and software

needed to connect two or more computer systems and/or devices

– Used to share hardware, programs, and databases across the organization

– Fosters teamwork, innovative ideas, and new business strategies

Types of Telecommunications Media (1)

• Twisted pair wire cable• Insulated pairs of wires historically used in

telephone service and to connect computer devices

• Coaxial cable• Consists of an inner conductor wire

surrounded by insulation, called the dielectric• The dielectric is surrounded by a conductive

shield, which is surrounded by a non-conductive jacket. Coaxial cable has better data transmission rate than twisted pair

Types of Telecommunications Media (2)

• Fiber-optic Cable• Many extremely thin

strands of glass or plastic bound together in a sheathing which transmits signals with light beams

• Can be used for voice, data, and video

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Personal Area Network• A PAN is a network that is used for

communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room

• It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet

• PAN’s can be wired or wireless– PAN’s can be wired with a computer bus

such as a universal serial bus: USB (a serial bus standard for connecting devices to a computer, where many devices can be connected concurrently)

– PAN’s can also be wireless through the use of bluetooth (a radio standard designed for low power consumption for interconnecting computers and devices such as telephones, printers or keyboards to the computer) or IrDA (infrared data association) technologies

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• A LAN is a network that is used for communicating among computer devices, usually within an office building or home

• LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users

• Is limited in size, typically spanning a few hundred meters, and no more than a mile

• Is fast, with speeds from 10 Mbps to 10 Gbps• Requires little wiring, typically a single cable connecting

to each device• Has lower cost compared to MAN’s or WAN’s

Local Area Network

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LAN basics

• LAN’s can be either wired or wireless. Twisted pair, coax or fiber optic cable can be used in wired LAN’s

• Nodes in a LAN are linked together with a certain topology. These topologies include:– Bus– Ring– Star– Branching tree

• A node is defined to be any device connected to the network. This could be a computer, a printer, a router, etc.

• A Hub is a networking device that connects multiple segments of the network together

• A Network Interface Card (NIC) is the circuit board that has the networking logic implemented, and provides a plug for the cable into the computer (unless wireless). In most cases, this is an Ethernet card inserted in a slot of the computer’s motherboard

• The Network Operating System (NOS) is the software (typically part of the operating system kernel) that communicates with the NIC, and enables users to share files and hardware and communicate with other computers. Examples of NOS include: Windows XP, Windows NT, Sun Solaris, Linux, etc..

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Network Topologies• Network Topology– A logical model that describes how networks

are structured or configured

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Network Topologies• Bus Topology

– Each node is connected one after the other (like christmas lights)– Nodes communicate with each other along the same path called

the backbone

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• Ring Topology– The ring network is like a bus network, but the “end” of the

network is connected to the first node– Nodes in the network use tokens to communicate with each other

Backbone

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• Star Topology– Each node is connected to a device in the center of the network

called a hub– The hub simply passes the signal arriving from any node to the

other nodes in the network– The hub does not route the data

Hub

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• Branching Tree Topology

Multiplexer

• Multiplexer– Allows several telecommunications signals to be

transmitted over a single communications medium at the same time

Pretty picture

Communicationslink

Multiplexor Front-endprocessor

Hostcomputer

Front-End Processor

• Front-end processor…– Special purpose computers that manage

communication to and from a computer system

Pretty picture

Incoming and outgoing jobs

Front-endprocessor

Mainsystem

Job 1

Job 2

Job 3

Job 4

Carriers and Services (1)• Carriers

• Organizations that take the responsibility of ensuring telecommunications can effectively take place between enterprises

• Common carriers• Long-distance telephone companies

• Value-added carriers• Companies that have developed private telecommunications systems and offer

their services for a fee• Switched lines

• Lines that use switching equipment to allow one transmission device to be connected to other transmission devices (e.g., standard telephone line)

• Dedicated line• A line that provides constant connection between two points. No switching or

dialing is needed

Carriers and Services (2)• Private branch exchange (PBX)

– Communication system that can manage both voice and data transfer within a location (e.g. a building) and to outside lines

• Wide area telecommunication service (WATS)– Billing method for heavy users of voice services

• Phone and dialing services– Includes automatic number identification (a.k.a. caller ID)– Integration of telephones and personal computers– Access code screening– Call priorities– One number portability (use anywhere)– Intelligent dialing (auto re-dial for a busy number)

• ISDN• ISDN = Integrated Services Digital Network• Technology that uses existing common-carrier lines to

simultaneously transmit voice, video, and image data in digital form

Pretty picture

Carriers and Services (3)

Networks and Distributed Processing

• Centralized processing– Data processing that occurs in a single location or facility

• Decentralized processing– Data processing that occurs when devices are placed at

various remote locations• Distributed processing– Data processing that occurs when computers are placed at

remote locations but are connected to each other via telecommunications devices

Network Concepts and Considerations

• Other network topologies– A topology is a logical model that describes how

networks are structured or configured• Hierarchical• Hybrid

Hierarchical• Uses treelike

structures with messages passed along the branches of the hierarchy

Hybrid• Network made up

of various types of topologies

Network Types• Local area network (LAN)– Connects computer systems and devices in the same

geographic area (can be Ring, Bus, Hierarchical, Star, Hybrid)

• Wide area network (WAN)– Ties together large geographic regions using microwave

and satellite transmission or telephone lines• International network– Links systems between countries

Terminal-to-Host Connection

– Applications and databases reside on the same host computer

– User interacts with the application using a “dumb terminal”

Hostcomputer

Target PC“dumb terminal”

REF: the thin-client set up at USIU – where you can’t use flash disks

File Server Connection

– Applications and databases reside on the same host computer

– File server transfers data and programs to PCs on the network, where these target PCs perform most of the processing

Hostcomputer

File downloaded to user

File server

Target PC

Client/Server Connection

– Applications and databases reside on specialized host computers

– Servers do most or all of the processing and transmit the results to the client

Client Server

Server ServerClient

Advantages & Disadvantages of Client/Server

Advantages Reduced cost potential Improved

Performance Increased Security

Disadvantages Increased cost potential Loss of control Complex multi-vendor

environment

Communications Software and Protocols (1)

• Communications software• Provides error checking, message formatting, communications

logs, data security and privacy, and translation capabilities for networks

• Network operating system (NOS)• Systems software that controls the computer systems and devices

on a network and allows them to communicate with each other

• Network management software• Enables a manager on a networked desktop to monitor the use of

individual computers and shared hardware, scan for viruses, and ensure compliance with software licenses

Communications Software and Protocols (2)

• Protocol• Rules that ensure communications among computers of

different types and from different manufacturers.

Communications Software and Protocols (3)

• Open Systems Interconnection (OSI) Model– Serves as a standard model for network architectures and

is endorsed by the International Standards Committee– Communication functions are represented in seven layers

to promote the development of modular networks. Designed to permit communication among different computers from different operating systems

– Seven layers (see figure 6.20)

Communications Software and Protocols (4)

• TCP/IP• TCP/IP = Transmission Control Protocol/Internet Protocol

Standard originally developed by the U.S. government to link defense research agencies; it is the primary communication protocol of the Internet

• Systems Network Architecture (SNA)• IBM communication protocol

• Ethernet• Protocol standard developed forLANs using a bus topology

• X.400 and X.500• An international standard for message handling and network

directories

Telecommunications Applications (1)

• Linking personal computers to mainframe computers– Download and upload information

• Voice mail– Enables users to leave, receive, and store verbal messages

for and from other users• Electronic mail (e-mail)– Enables a sender to connect a computer to a network,

type messages, and send it to another person on the network

Telecommunications Applications (3)

• Videoconferencing– Allows participants to conduct long-distance

meetings “face to face” while eliminating

Pretty picture

• Thanks