CSCD 218 : DATA COMMUNICATIONS AND NETWORKING 1 LECTURE 1 INTRODUCTION AND BASIC CONCEPTS DATA COMMUNICATIONS LECTURER : FERDINAND KATSRIKU (PhD)

What Is Data Communications?  When we communicate we are sharing information Local sharing, e.g. face-to-face Remote 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, the communicating devices must be a part of a communication system made up of a combination of hardware and software.

Effective Data Communications Depends 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 a reasonable 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 transmitted Transmitter : Converts data from source into transmittable Signals Transmission System : Carries data from source to destination Receiver : Converts received signal into data Destination : Takes and uses incoming data

Simplified Communications Model An Example

Communications Tasks Simplified 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 and efficient manner; focusses on individual links Networks : communications across set of links; Wide Area Networks, Local Are Networks, The Internet

A Data Communications Model

Basic Terms and Concepts Data 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, Broadcasting II.Topology : Bus, tree, Ring, Mesh etc III.Transmission Mode : Half Duplex,Simplex, Full Duplex IV.Network Types : LAN, WAN,WLAN,MAN,SAN etc V.Internetworks

The Transmission of Information Transmission and Transmission Media  How to convert information into transmittable electromagnetic signal?  What transmission media to use? Communication Techniques  How to encode information into a signal?  How to deal with errors? Transmission Efficiency  How 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.computer networkgatewaysroutingpackets Local Area Network : is a computer network that interconnects computers within a limited area.computer network  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 : 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.network server  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 P2P 1.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 Networks 1.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 1.More expensive than a peer-to-peer network you have to pay for the start up cost. 2.When the server goes down or crashes all the computers connected to it become unavailable to use. 3.When you expend the server it starts to slow down due to the Bit rate per second. 4.When everyone tries to do the same thing it takes a little while for the server to do certain tasks.