Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill Technology EducationMcGraw-Hill Technology EducationCopyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.

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Chapter 9A


Network Definition

• Set of technologies (hardware, software,

media) that connects computers

• Allows communication and collaboration

between users

• Data Communications:

– The electronic transfer of information between computers.

– Information can be text, voice, audio and video traffic.


Network Definition

• When most people think of a network,

• they imagine several computers in a

single location

• sharing documents and devices such as


• But a Network can include all the

computers and devices in a department,

a building , or multiple buildings,


The Uses of a Network

• Network allows many users to access

shared data and programs instantly.

• Data and programs are stored on a

network and are shared.

• Individual users can reduce the need for

programs on their computers.


The Uses of a Network

• Simultaneous access to data

– Data files are shared

• Access can be limited

– Shared files stored on a server – Software can be shared

• Site licenses

• Network versions • Application servers


The Uses of a Network

• Simultaneous access to data:

– There are moments in business when

several workers may need to use the same data at the same time

– A good example is a company’s quarterly sales report which needs to be viewed an updated by several managers.

– Without a network, workers must keep separate copies of data store on their computers.


The Uses of a Network

• Simultaneous access to data:

– When data is modified on one computer, others become outdated.

– It becomes difficult to determine which copy of the data is most current.

• Solution:

– Companies can solve this problem by storing commonly used data at central location called Network server.


The Uses of a Network

• Network Server:

– A central computer with a large storage device and other resources that all users can share.

– If the server stores data files for users to access, It is also called a file Server.

– The business can store a single copy of data file on the server that employees can access

– If one user makes a change to the file,


Sharing Data

File server contains documents used by other computers.


The Uses of a Network

• Application Server: Most office

workers also use the software or

programs from servers.

• If an environment where PCs are not

networked, a separate copy of each

program must be installed on every


• This can be costly for two reasons:

– Software can be expensive ( buy many copies) – Installing and configuring a program on different


The Uses of a Network

• Site Licenses: purchase site license for


• A business buy a single copy of an application and then pays the developer for a license to

copy the application onto a specified number of computers.

• Under a site license each user has complete, individual copy of the program running on his PC

• Thus business generally pays less money then it would by purchasing a complete copy of the


The Uses of a Network

• Network versions:

– Only one copy of the application is stored on the server.

– Connect user’s computers to a central server

– And enable users to share a network version of a program.

– Workers need to load program from server into the RAM of their on desktop.


The Uses of a Network

• Shared peripheral device

– Printers and faxes are common shares – Reduces the cost per user

– Devices can be connected to the network – Print servers control network printing


The Uses of a Network

• Personal communication

– Email • Instantaneous communication – Conferencing • Tele conferencing • Video conferencing • Audio conferencing

• Data-conferencing (shared white boards, application sharing)

– Voice over IP


The Uses of a Network

• VOIP: System’s bypass the need for the

cost of regular telephone service by

using the company’s internal network to

send and receive phone calls.

• It transmits the sound of your voice over

a computer network

• Uses Internet protocol (IP) rather than

sending the signals over traditional


The Uses of a Network

• Easier data backup

– Backup copies data to removable media – Server data backed up in one step

– Employees can access storage device through a network.


Common Network Types

• Local Area Network (LAN)

– Data communication system

– Contains printers, servers and computers – Systems are close to each other

– Contained in one office or building – Physically connected using cables


Common Network Types

• Wide Area Networks (WAN)

– Two or more LANs connected – Over a large geographic area

– Typically use public or leased lines

• Optic fibers • Satellite

– The Internet is a WAN

– For example a company may have head office in one city and marketing offices in different citites.


Hybrid Network Types

• Campus Area Networks (CAN)

– A LAN in one large geographic area

– Resources related to the same organization – Each department shares the LAN


Hybrid Network Types

• Metropolitan Area Network (MAN)

– Large network that connects different organizations


Hybrid Network Types

• Home Area Network (HAN)

– Small scale network (Home network)

– Connects computers and entertainment appliances: • Printers • Telephone • VCR’s • DVDs • Televisions • Video games


Hybrid Network Types

• Personal Area Network (PAN)

– Very small scale network

– Range is less than 2 meters


How Networks Are Structured

• Server based network

– Node is any network device

– Servers control what the node accesses – Users gain access by logging in

– Server is the most important computer – Users gain access to files, printers and

other network based objects

– Users must log-on to the network to access resources.


How Networks Are Structured

• Client/Server network

– Nodes and servers share data roles – Nodes are called clients

– Individual computers share the processing and storage workload with central server. – Servers are used to control access

– The network requires special software for the nodes and server.


How Networks Are Structured

• Client/Server network

– Example: Database software

• Accessed by many computers on the network. • Database is stored on the network server

• DBMS: allows the users to work with the database on server

• Clients machine have DBMS to access DB


How Networks Are Structured

• Peer to peer networks (P2PN)

– All nodes are equal

– Nodes access resources on other nodes – Each node controls its own resources

– Most modern OS allow P2PN i.e.

• Windows 9x, Windows 2000 professional • Windows Me, Windows XP, MAC OS

– Enables the users to set a simple peer-to-peer network using no other


Network Topologies

• Topology: Important feature of LAN

– Logical layout of wires and equipment – Network designs considers:

• Distance b/w computers

• The type of computers and cabling • The speed at which data must travel • Cost of setting up network

– Choice affects

• Network performance • Network size


Network Topologies

• Packets

– Pieces of data transmitted over a network

• Packets are created by sending node • Data is reassembled by receiving node

– Packet header

• Sending and receiving address

• Network reads each packet’s header to determine where to send it.

– Packet payload


Network Topologies

• Topology:

• In the Internet environment Packets are called data grams.


Network Topologies

• Bus topology

– Also called linear bus

– One wire connects all nodes – Terminator ends the wires – Advantages

• Easy to setup

• Small amount of wire

– Disadvantages


Bus Topology


Network Topologies

• Star topology

– All nodes connect to a hub

• Packets sent to hub

• Hub sends packet to destination

– Advantages

• Easy to setup

• One cable can not crash network

– Disadvantages

• One hub crashing downs entire network • Uses lots of cable


Network Topologies

• Ring topology

– Nodes connected in a circle – Tokens used to transmit data

– Last node connects to first node – Advantages

• Time to send data is known • No data collisions

– Disadvantages


Network Topologies

• Mesh topology

– All computers connected together

– A cable runs from every computer to every other computer.

– Internet is a mesh network

– Advantage

• Data will always be delivered

• If one connection goes down , there are other ways to route the data

– Disadvantages


Network Media

• Links that connect nodes

• Choice impacts

– Speed – Security – Size


Wire Based Media

• Twisted-pair cabling

– Most common LAN cable

– Called Cat5 or 100BaseT

– Four pairs of copper cable twisted

– May be shielded from interference

– Speeds range from 1 Mbps to 1,000 Mbps


Wire Based Media

• Coaxial cable

– Similar to cable TV wire

– One wire runs through cable – Shielded from interference – Speeds up to 10 Mbps


Wire Based Media

• Fiber-optic cable

– Data is transmitted with light pulses

– Glass strand instead of cable

– Immune to interference – Very secure

– Hard to work with – Speeds up to


Wireless Media

• Data transmitted through the air

• LANs use radio waves

• WANs use microwave signals

• Easy to setup


Network Hardware

• Network interface cards

– Network adapter

– Connects node to the media


Network Hardware

• Network linking devices

– Connect nodes in the network – Cable runs from node to device


Network Hardware

• Hubs

– Center of a star network

– All nodes receive transmitted packets – Slow and insecure


Network Hardware

• Switches

– Replacement for hubs

– Only intended node receives transmission – Fast and secure


Network Hardware

• Bridge


Network Hardware

• Router

– Connects two or more LANs together – Determine best route for the packet


Network Cabling

• Cabling specifications

– Bandwidth measures cable speed

• Typically measured in Mbps

– Maximum cable length


Network Cabling

• Ethernet

– Very popular cabling technology – Maximum bandwidth 10 Mbps


Network Protocols

• Language of the network

– Rules of communication – Error resolution

– Defines collision and collision recovery – Size of packet


Chapter 9A




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