Importance of

Communication

What is a network?

Networks

What is a network?

• A network consists of two or more computers that are linked in order to:• share resources

(such as printers and CD-ROMs),

• exchange files, or • allow electronic

communications

ADVANTAGES of NETWORKS• A network makes it easier to

communicate (between computers)• Eg an email is faster than ‘normal

mail’

• There are 2 major ways networks advantage people and organisations

1. Save money by sharing resources2. Remote services

ADVANTAGES of NETWORKS

1. Save money by sharing resources• E.g. teacher sends notes via email instead of

printing, photocopying, collating, stapling & handing out

• Sharing internet connection resources• Many people able to use one connection

• Sharing printing resources• Many people able to use one printer

• Sharing other resources• Like faxes, CD-ROM towers, network storage &

directory services

ADVANTAGES of NETWORKS

2. Remote services• Eg customers ordering over the

internet• Eg business to business

transactions• Gives customers more control (and

reduces 3rd party errors/ human errors)• Eg ATMs

USING NETWORKS• The cost of equipment used to

connect a computer to a network is now relatively cheap

• The software used to control networks has developed and improved so that most users do not know there is software handling such tasks• The use of networks has become

“transparent” to the user

How are they linked?

• Computers on a network may be linked through: • cables, • telephone lines, • radio waves,

satellites or • wireless

technologies

COMMON NETWORKS

• Cable TV• (traffic is just one way)

• Telephone system• (traffic is two-way)

• Mobile phones• (use radio waves rather than cables or

wires)

The two basic types of networks include:

• Local Area Networks (LAN)

• Wide Area Networks (WAN)

LAN

WAN

Local area networks

• LANs are confined to a relatively small area such as a school or a building

• LANs usually have one computer designated as the file server

• Other computers are connected to the network by cables connecting network interface cards in each computer

Wide Area Networks

• WANs connect larger areas, such as whole states, or even the world.

• Transoceanic cables and satellites are used to connect WANs

Protocol

• A protocol is a set of rules that governs the communications between computers on a network

• These rules include guidelines that regulate the method of access, types of cabling and speed of data transfer

PROTOCOL =

SET OF RULES ABOUT

COMMUNICATIONS

BETWEEN

NETWORKS!

The most common protocols are:

• Ethernet

• Token Ring

• TCP/IP

Protocol = a formal description of a set of rules and conventions that govern how devices on a network exchange information

Ethernet

• Most widely used• Uses an access

method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection

What does that mean?• Each computer in the

network ‘listens’ to the cable before sending anything through the network. If the network is clear, the computer will transmit.

• If another computer is already transmitting on the cable, the computer will wait and try again when the line is clear

A bit like waiting for your younger sister to get off the telephone perhaps?

Ethernet (continued)• Sometimes, two computers

attempt to transmit at the same instant. When this happens, a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. It is normal to have collisions using this method, but the delays caused by collisions and transmissions is small, and does not effect speed of transmission on the network

CSMA/CD =Carrier Sense Multiple

Access /Collision Detection

Fast Ethernet

• To allow for faster transmission, the Ethernet protocol has developed a new standard that supports 100 Mbps

• Fast Ethernet requires the use of more expensive equipment and network cards

Token Ring

• Token ring protocol involves ‘token-passing’.

• It is not as popular as Ethernet protocol

A single electronic ‘token’ moves around the ring from

one computer to the next. If a computer wishes to transit

and receives an empty token, it attaches data to the token which then proceeds around the ring until it comes to the computer the data is meant

for.

ATM

• Stands for Asynchronous Transfer Mode

• Transmit data at a speed of 155 Mbps and higher

• Works by transmitting all data in small packets of fixed size (other protocols transfer variable size packets)

• Like FDDI , is most often used to connect two or more LANs

Where does TCP/IP fit into all this???

• TCP/IP is the protocol that is used for the transmission of information over the Internet

• IP (Internet Protocol) - the main delivery system for information over the Internet

• TCP (Transport Control Protocol) - used to break apart and rebuild information that travels over the Internet

Network Hardware

• Network hardware includes:• Computers• Peripherals• Interface cards and• Other equipment

needed to perform data processing and communications within the network

File servers

• A very fast computer with a large amount of RAM and storage space along with a fast network interface card

• The network operating system software resides on this computer

Workstations

• All computers connected to the file server on a network are called workstations

Network interface cards

• The network interface card (NIC) provides the physical connection between the network and the computer workstation.

• Most NICs are internal with the card fitting into an expansion slot in the computer.

• Three common network interface connections are Ethernet cards, Local Talk connectors and Token Ring cards

Ethernet cards

• The most common Network Interface Cards are Ethernet cards

• They contain connections for either coaxial or twisted pair cables, or both

Twisted pair cable

Co-axial cable

Concentrators / Hubs• A concentrator is a device

that provides a central connection point for cables from workstations, servers and peripherals

• Hubs are multi-slot concentrators

• A hub is a device that takes any incoming signal and re-broadcasts it down all the outgoing wires connected to it

• Hubs can have from 5 ports to 128 ports

• Can transmit & receive at up to 100Mbps

Switches• While hubs provide an

easy way to scale up and shorten the distance that the packets must travel to get from one node to another, they do not break up the actual network into discrete segments. That is where switches come in.

• An alternative to hubs are switches• A switch stores the address of every device down each

wire leading from the switch• Usually found in larger networks

Switches (continued)• A vital difference between a hub and a switch

is that all the nodes connected to a hub share the bandwidth among themselves, while a device connected to a switch port has the full bandwidth all to itself.

• Think of a switch as a ‘clever’ hub

Routers (continued)

Modems

• A modem is a device that is used to send a computer’s digital signal over a telephone line – where the signal must be changed to analog.

• Different types of modems:• Dial-up• Integrated Services Digital Network

(IDSN or DSL)• Cable

Cabling• Network cabling is

the medium through which information usually moves from one network device to another

• There are several different types of cable commonly used in LANS

• Some networks use a variety of cable types within the one network

Unshielded Twisted Pair (UTP) Cable

• Twisted pair cables come in two varieties: shielded and unshielded. Unshielded (UTP) is the most popular

• Shielded twisted pair is used only in environments where there may be electrical interference

UTP (continued)• UTP has four pairs of wires inside the jacket• Each pair is twisted with a different number of

twists per inch to help eliminate interference from adjacent pairs

UTP Connector

• The standard connector for UTP cabling is an RJ-45. It looks like a telephone style connection

Coaxial cable

• Coaxial cable has a single copper conductor at its centre with a plastic layer between the centre conductor and the braided metal shield

• Although coaxial cabling is difficult to install, it is highly resistant to signal interference

Coaxial cable connectors

• Carries data at 10Mbps over 185metres• Carries signal both directions, usually used

when no hubs or switches• The most common type of connector used

with coaxial cables is the BNC connector

Fiber Optic Cable• Fiber optic cabling consists of a center

glass core surrounded by several layers of protective materials

• It transmits light rather than electronic signals

• It is the standard for connecting networks between buildings, due to its immunity to the effects of moisture and light

Fiber Optic (continued)• Fiber optic cable has the ability to transmit

signals over much longer distances than coaxial or twisted pair

• It can also carry information at vastly greater speeds (Transmits light pulses up to 2km & over 1000 frequencies can be transmitted along a strand at one time)

• Fiber optic cable is more difficult to install than other cabling & is expensive

Wireless LANS• Wireless networks use high frequency radio

signals to communicate between the workstations and the fileserver or hubs.

• Disadvantages of wireless networks are:• they are expensive (relatively), • provide poor security, • are susceptible to interference and • are slower than cabled networks

Wireless Transmission

• Wireless transmission includes the use of:• Radio waves

• Bluetooth

• Microwaves• Satellite• Infra-Red

Network Operating Software

• Network operating systems co-ordinate the activities of multiple computers across a network

• The two major types of network OS are:• Peer-to-peer• Client/server

Peer to peer network OS• In peer to peer network OS,

there is no file server or central management source; all computers are considered equal

• Peer to peer networks are design primarily for small to medium LANS

• AppleShare and Windows for Workgroups are examples of programs that can function as peer to peer

Client/Server network OS• Client/server network OS

centralise functions and applications in one or more dedicated file servers.

• The file server provides access to resources and provides security

• Novelle Netware and Windows NT Server are examples of client/server network operating systems

Network Operating Systems

• There are 3 major network operating systems used with personal computers• Windows (2000 then XP now - Vista)• Novell• Apple

• The network operating system is software that controls traffic on the network and defines how well we communicate with each other

• Having all machines in a network use the same operating system is preferable, especially for instructions & maintenance

Topology

• The physical topology of a network refers to the configuration of cables, computers and other peripherals.

• The main types of network topologies are:• Linear Bus• Star• Ring• Tree or Hybrid

Linear Bus• A linear bus topology consists of a main run

of cable with a terminator at each end. All servers workstations and peripherals are connected to the linear cable

Star

• A star network is designed with each node (file server, workstation, peripheral) connected directly to a central network hub or server

Ring

• A ring network is one where all workstations and other devices are connected in a continuous loop. There is no central server

Tree or hybrid• A tree or hybrid

topology combines characteristics of linear bus and star and/or ring topologies.

• It consists of groups of star-configured workstations connected to a linear bus backbone cable

IMPROVEMENTS THROUGH USING NETWORKS

1. Improvements in efficiency• Save time (single resource, many

users – no queues)• Save money (single resource, many

users)• Save effort (don’t need to move from

machine to machine)• Communication is simpler & faster

(instant – in ‘real time’

IMPROVEMENTS THROUGH USING NETWORKS (cont)

2. Improvements in effectiveness• Because communication is easier & faster,

people are more likely to communicate• As well as improved quantity & speed,

quality has also been improved (eg group work & instant updates & less duplication)

IMPROVEMENTS THROUGH USING NETWORKS (cont)

3. Improvements in information systems• Networks allow data to be shared among

users and enables users to retrieve information from more than one source

• This synchronisation avoids data duplication• Data manipulation can be spread over a

number of computers, speeding up processing

IMPROVEMENTS THROUGH USING NETWORKS (cont)4. Improvements in meeting organisational

goals• Save time by having multiple users working

on same data set simultaneously• Also when passing on data to other workers,

there is very little time & effort involved if networks are used for the data movement

• Improved productivity thanks to improved efficiency & effectiveness

Network SecurityEncryption Software

• Makes normally readable plain text a mixture of characters

• This ‘scrambling’ is done using algorithms

Eg Chris may become…Hsirc

Or3818919

Or#+*’?

Network SecurityUsernames & Passwords• Network policies, profiles –Many

organisations now use networks to enable employees to access data stored in different locations• To enable employees to gain access to

some files but not others, a network administrator will establish a series of network policies and profiles

• For example, needing a username and password

Network Security Firewalls

• Firewalls are based on a combination of hardware and software that only allow authorised network traffic to pass through the ‘gate’ which they protect

Network Security Anti-Virus & Malware Protection

• Protects computers by detecting the presence of viruses as the machine boots up

• Scans files for virus signatures, or virus-like activity

• Can be automatically removed or a warning flashed to the user

Logical Design of a Network• Logical Design Factors:

• Ability to fulfil required functions• Software Interface• Ease of Hardware Use• Procedures

• Applications• Cost• Security • Access to required information & resources

• Inclusiveness

• LAN protocol• Expansion potential• Compatibility of components

Physical Design of Networks

• Often networks can become very complicated

• A way of visually showing the physical devices & communication lines present in a network is with a network diagram

Network Diagram