CS509 Computer Networks Lecture 1 Dr. Nermin Hamza

 Overview  Network protocols  Data communication : data and media  Signal encoding  Data link control protocol 2 Aim of Course

 Lecture Notes.  Sheets.  Data and Computer Communications. 9 th edition, William Stallings 3 Resources

 Three forces are driving the evolution of data communications and networking Growth of communication traffic:  Voice traffic  telephone  Data traffic  Internet access, video conferencing  Challenges (to the network service providers):  how to maximize the capacity and minimize the cost? 4 What are the trends?

Advances in technology:  Faster and cheaper computing and communications  Networks are more intelligent: quality of service (QoS)  Internet, Web, intranets, extranets, etc.  Pervasive computing/ubiquitous computing 5 What are the trends?

Networks Communication Model SourceTransmitter Transmission system ReceiverDestination

7 Components of Data Communication Receiver Sender Message Protocol Rules. Rules. Protocol Transmission Medium

 Computer Communication: – The exchange of information between computers for the purpose of cooperative action.  Computer Network: – A collection of computers interconnected via a communication network. 8 Computer Communication Architecture

1. Message: data. 2. Sender: The device that send the message. 3. Receiver: The device that receive the message. 4. Transmission Medium: The physical path between sender and receiver, the message travel. 5. Protocol: Is a set of rules that governs data communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating. 9 Components of Data Communication cont.

10 A Communication Model Input Information m Input data g or signal g(t) Transmitted signal s(t) Received signal r(t) Output data g’ or signal g’(t) ’ Output Information m’ Transmission medium Transmitter Input Device Output Device Receiver Source SystemDestination System Sender Receiver

Data Communications Simplified Data Communications Model

1. Delivery: The system must deliver data to the correct destination. 2. Accuracy:  Data delivered accurately.  Altered data which left uncorrected are unusable. 3. Timelines: The system must deliver data in timely manner without delay (real- time). delay 4. Jitter: Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. 12 Data Communication Characteristics

Communications Tasks Transmission system utilizationAddressing InterfacingRouting Signal generationRecovery SynchronizationMessage formatting Exchange managementSecurity Error detection and correctionNetwork management Flow control

 Data encoding: The process of transforming input data or signals into signals that can be transmitted 14 Common Communication Tasks

 Signal generation: - Generating appropriate electro-magnetic signals to be transmitted over a transmission medium  Synchronization: -Timing of signals between the transmitter and receiver ; when a signal begins and when it ends; duration of each signal 15 Common Communication Tasks

 Error detection and correction: - Ensuring that transmission errors are detected and corrected  Flow control: - Ensuring that the source does not overwhelm the destination by sending data faster than the receiver can handle 16 Common Communication Tasks

 Multiplexing: -A technique used to make more efficient use of a transmission facility. This technique is used at different levels of communication.  Addressing: -Indicating the identity of the intended destination.  Routing: -Selecting appropriate paths for data being transmitted 17 Common Communication Tasks

 Message formatting: - Conforming to the appropriate format of the message to be exchanged 18 Common Communication Tasks

 Security: -Ensuring secure message transmission.  Systems management: - Configuring the system, monitoring its status, reacting to failures and overloads, and planning for future growth 19 Common Communication Tasks

 Growth of number & power of computers is driving need for interconnection.  Rapid integration of voice, data, image & video technologies.  Two broad categories of communications networks:  Local Area Network (LAN)  Wide Area Network (WAN) Networking