1. Data Communications

2. Part 1
Lecture 1 Introduction
Lecture 2 Network Models

3. Introduction

4. What is data Communication
Communication means sharing of information on local or remote, local communication occur face to face and remote communication takes place over distance.
The term telecommunication, which includes telephone, telegraphy and television, means communication at distance (tele is Greek for far)
The word data refers to information presented in whatever form agreed upon by the parties creating and using those data

5. What is data Communication Cont..
It can be defined as the process of exchanging data between two devices or more via some form of transmission medium such as a wire cable.
It enables the movement of electronic or digital data between two or more nodes, regardless of geographical location, technological medium or data contents.
For data communication occur communicating devices must be part of a communication system made up of a combination of hardware and software

6. Fundamental characteristics of effective data communication system
Delivery. The system must deliver data to the correct destination. Data must be received by intended device or user and only by that device or user
Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.
Timeliness. The system must deliver data in timely manner. Data delivered late are useless
Jitter. refers to the variation in the packet arrival time.

7. Five components of data communication

8. Sender: The sender is the device that sends the message (data)
Sender: The sender is the device that sends the message (data). It can be a computer, workstation, mobile handset or a video camera
Receiver: The receiver is the device that receives the message . It can be a computer, workstation, mobile handset or television
Message: The message is the information (data) to be communicated. It can be a text message, number, picture, sound, video or a combination of these
Medium: The transmission medium is the physical path by which a message travels from sender to receiver. It could be a cable (twisted pair), fiber optic or air
Protocol: A protocol is a set of rules that govern computer communication. It present an agreement between communicating devices. A protocol define what is communicate, how it is communicated and when it is communicate

9. Direction of Data Flow

10. Simplex Half-Duplex Full-Duplex
Transmission Modes or Direction of data flow
The direction of a signal between two devices is defined by a transmission mode. Or The transmission mode defines the direction of a signal between two devices
Simplex
Half-Duplex
Full-Duplex

11. Simplex
In the simplex mode the communication is unidirectional. Only one can send data and other can receive. No any other possibility is available. A remote is an example of simplex mode.

12. Example of Simplex Communication
For example, in TV and radio broadcasting, information flows only from the transmitter site to multiple receivers.
Garage door openers
Baby monitors
Wireless microphones
Surveillance cameras
Communication between a mouse and a computer
Radio navigation beacons and radiolocation services such as GPS
Printers

13. Half-Duplex Transmission
Half Duplex Mode: In the Half-duplex (sometimes it is called an alternating connection or semi-duplex) mode, the data can be transmitted from one direction to the other. The terminals have ability to either receives or sends out the data. However, sending and receiving can not be done at same time. For example; FAX (it can sends or receives letter but not in same time).

14. Half-duplex

15. Full-Duplex Transmission
Full Duplex Mode: In full duplex mode both devices can send and receive data at the same time. It has two way traffic at the same time or its like a two lane bridge on a two-lane highway. Online communication such as MSN-hotmail, Yahoo messanger, google talk, facebook chatt-room and Skype telephone are the one of the examples of software, which are in full-duplex and also the telephone network (example landline and mobile) is an example of full duplex mode.

16. Networks

17. Networks
A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.

18. Distributed Processing
Most networks use distributed processing, in which a task is divided among multiple computers.
Instead of one single large machine being responsible for all aspects of a process, separate computers (usually a personal computer or workstation) handle a subset.

19. Network Criteria Most important Network Criteria are Performance
Reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness in catastrophe
Security issues includes protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for breaches and data losses.

20. Performance Measured using transit time and response time.
Transit time is amount of time required for a message to travel from one device to another.
Response time is the elapsed time between an inquiry and response.
The performance of network depends on number of factors, including the number of users, the type of transmission medium, capability of connected hardware and efficiency of software

21. Network Topologies
What is a topology? Topology is the physical or logical connections of communicating devices

23. Mesh Topology

24. Star topology

25. Bus Topology

26. Ring Topology

27. Categories of Networks
A network is a set of devices (nodes) connected by media links. A node can be a computer , printer, or any other devices capable of sending and /or receiving data generated by another node in the network

28. LAN
LAN is usually privately owned and interconnect devices in a single office, building, or campus (see the figure below)

29. MAN
MAN is designed to extend over an entire city. It may be single network such as cable television network , or it may be a means of connecting a number of LANs into a large network so that resources can be shared. For example, UDSM with many campuses mliman, kunduchi, and DUCE .

30. WAN
WAN provides a long-distance transmission of data, voice, image and video information over large geographical area that may comprises a country, a continent , or even the whole world. For example the internet, Tigo Network, Vodacom, and Airtel

31. Protocols and Standards

32. Protocols Protocol is the set of rules that governs data communication
Protocol defines what is communicated, how it is communicated, and when it is communicated
The key elements of the protocol are:
Syntax
Semantic
Timing

33. Syntax
Syntax refer refers to the structure or format of the data, meaning the order in which they are presented. For example, a simple protocol might expect the first eight bits of the data to be the address of the sender , the second 8 bit to be the address of the receiver, and the rest of the stream to be the message itself

34. Semantic
Semantic refer the meaning of each section of the bits. How is a particular pattern to be interpreted, and what action is to be taken regarding that interpretation? For instance, does an address identify the route to be taken or the final destination of the message

35. Timing
Timing refers to two characteristics: When data should be sent and how fast they should be sent. For example, if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and some data will be lost.

36. Standards
Standards provides a model for development that make it possible for product to work together regardless of individual manufacturer
Standards are essential in creating and maintaining an open competitive market for equipment manufacturer.
Standards provides guidelines to manufacturers, vendors, government agencies and other service providers
Data communication standards fall into two categories: de-facto (means by fact or convention) and de jure (mean by law or by regulation)

37. de jure standards are standards that have been legislated by an officially recognized body.
de facto standards are standards that have not been approved by an organized body but have been adopted through widespread use
De facto
Proprietary- they called closed systems because they close off communication between systems produced by different vendors
Nonproprietary- they are called open standards because the open communication between different systems

38. Standards Organizations
Standards creation committees (e.g. ISO, ITU, ANSI and , IEEE)
Forum (e.g. forum of wireless communication)
Regulatory agencies (e.g. TCRA, FCC)

39. Multiple Choice Question for Practice
Key terms (words)
Refer all key terms for this lecture
Multiple Choice Question for Practice
Resource from the internet:
Site for unedited slides of Fourth Edition

40. Key terms for Lecture 1 Bus topology Data communications
de facto standards
de jure standards
Full-duplex mode, or duplex
Half-duplex mode
Internet
Local Area Network (LAN)
Mesh topology
Metropolitan Area Network (MAN)
Network
Node
Physical topology
Protocol
Ring topology
Semantics
Simplex mode
Star topology
Syntax
Timing
Transmission medium
Wide Area Network (WAN)