CSCD 218 : DATA COMMUNICATIONS AND NETWORKING 1

LECTURE 1INTRODUCTION AND BASIC

CONCEPTSDATA COMMUNICATIONS

LECTURER : FERDINAND KATSRIKU (PhD)

What Is Data Communications? When we communicate we are sharing information

Local sharing, e.g. face-to-faceRemote sharing, e.g. over some distance

Data: information being shared, e.g. text, numbers, images, audio, video

Data Communications: exchange of data between two (or more) devices via some transmission medium

For Data Communication to occur, thecommunicating devices must be a part of a communication system made up of a combination of hardware and software.

Effective Data CommunicationsDepends on four (4) fundamental characteristics : Delivery : the data must be delivered to the correct

destination. Accuracy : the data received must be accurate

representation of the data sent. Timeliness : the data should be delivered within areasonable time. Jitter : describes timing errors within a system.

Components of Data Communication System

Five components make up a data communication system :I. Sender : The sender is the device that sends the data

message. It can be a computer ,workstation ,telephone handset ,video camera etc..

II. Message : The message is the data information to be communicated. It can be either text, numbers or audio or video or any combination of these types.

III. Transmission Medium : the physical path by which a message travels from sender to receiver.It should be a twisted –pair wire ,co-axial cable,fiber optic cable or Radio waves etc.

Components of Data Communication System (Cont)

IV. Receiver : The receiver is the device that receives the messages. It can be a computer, workstation , telephone handset ,video camera or television etc.

V. Protocols : A protocol is a set of rules that govern the data communications. It represents an arrangement between the communicating devices. Without a protocol two devices may be connected but can not communicate.

Components of Data Communication System (Cont)

Fig 1.1 Components of Data Communication

Simplified Communications Model

Source : Device that generates data to be transmittedTransmitter : Converts data from source into transmittable

SignalsTransmission System : Carries data from source to destinationReceiver : Converts received signal into dataDestination : Takes and uses incoming data

Simplified Communications Model

An Example

Communications TasksSimplified communications model makes it look easy . . . but there are many tasks to be performed in a data communications system.

Categorizing Communication Technologies

Data Communications : transmitting signals in reliable andefficient manner; focusses on individual links

Networks : communications across set of links; Wide AreaNetworks, Local Are Networks, The Internet

A Data Communications Model

Basic Terms and ConceptsData is being transmitted between two devices namely transmitter and receiver. To understand this entire phenomena we need to know about five basic concepts .They are :I. Line Configuration/Transmission Line ; Point-to-Point ,

Multipoint , BroadcastingII. Topology : Bus, tree, Ring, Mesh etcIII. Transmission Mode : Half Duplex ,Simplex, Full DuplexIV. Network Types : LAN, WAN,WLAN,MAN,SAN etcV. Internetworks

The Transmission of InformationTransmission and Transmission Media

How to convert information into transmittable

electromagnetic signal?What transmission media to use?

Communication TechniquesHow to encode information into a signal?How to deal with errors?

Transmission EfficiencyHow to efficiently utilize/share communications system?

Network Interconnections The practice of connecting a computer network with other

networks through the use of gateways that provide a common method of routing information packets between the networks.

Local Area Network : is a computer network that interconnects computers within a limited area . Such as a home, school, computer laboratory, or office

building, using network media.

LAN-TO-LAN CONNECTIONS

Connecting two or more LANs together using a router.

Peer-to-Peer : A peer-to-peer network is created when two or more PCs are connected and share resources without going through a separate server computer. All of the computers are equal and therefore known as

peers, Peer – to – peer networking is perhaps one of the most useful and yet Misunderstood technologies to emerge in recent years.

Advantages of P2P1. Easy and simple to set up only requiring a hub or a switch

to connect all computers together.2. If one computer fails to work all the other computers

connected to it still continue to work.

Advantages P2P (Cont)3. All the resources and contents are shared by all the peers, unlike server-client architecture where Server shares all the contents and resources.4. If one computer fails to work all the other computers connected to it still continue to work.5. The over-all cost of building and maintaining this type of network is comparatively very less.

Disadvantages of P2P

1. Security in this system is very less ; viruses, spywares ,trojans, etc malwares can easily transmitted over this P-2-P architecture.

2. Data recovery or backup is very difficult. Each computer should have its own back-up system.

3. It does not run efficient if you have many computers, it is best to used two to eight computers.

A Peer-to-Peer Network

Client/Server

In client/server network architecture, there is a dedicated computer (server) which allows or provides resources or services to other workstations or computers (clients) on the network.

A client/server network is a system where one or more computers called clients connect to a central computer named a server to share or use resources.

The client request for a service or a resource from the server by sending a request. The server in turn respond to the client’s request.

At least one of the computers is used to "serve" other computers referred to as "clients“.

A Client/Server Model

Advantages of Client/Server Networks1. A client server can be scaled up to many services that can also be used

by multiple users.2. All the data is stored onto the servers which generally have far greater

security controls than most clients. 3. Easy to backup; Archiving and backup can be carried out over the

network.4. Operating system and software updates can be deployed remotely

over the network.Disadvantages of Client/Server Networks

5. More expensive than a peer-to-peer network you have to pay for the start up cost.

6. When the server goes down or crashes all the computers connected to it become unavailable to use.

7. When you expend the server it starts to slow down due to the Bit rate per second.

8. When everyone tries to do the same thing it takes a little while for the server to do certain tasks.