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Welcome ! BENG 4522 Data Communications & Computer Network Semester 1 2008/2009 Zulhani Bin Rasin B-2/9 Office : 06-5552291 H/p : 012-3767263 Email : zulhani@utem.edu.my Beng4522.wordpress.com BENG 4522 Data Communications & Computer Networks

Chapter 1 : Introduction to Computer Networks • Outline • Communication model • Type of network • Network models • Network components • Network topology • Network technology and applications BENG 4522 Data Communications & Computer Networks

1.0 : The definition • Computer Network – an interconnected collection of devices (computers) which are : • Cooperative • Cooperative action is required between components • No master-slave relationships • Autonomous • All components are capable of independent action • Any resource is capable of refusing requests • Mutually Suspicious • Components verify requests BENG 4522 Data Communications & Computer Networks

1.1 : Communication Model BENG 4522 Data Communications & Computer Networks

1.1 : Communication Model • Source • Generate data to be transmitted • Transmitter • Convert data a transmittable signals • Transmission system • Carries data • Receiver • Convert back the received signals in to the original data • Destination • Takes the incoming data BENG 4522 Data Communications & Computer Networks

1.1 : Communication Model BENG 4522 Data Communications & Computer Networks

1.2 : Communication tasks • Task in communication model • Transmission system utilization • Interfacing • Signal generation • Synchronization • Exchange management • Error detection and correction • Flow control • Addressing • Routing • Recovery • Message formatting • Security • Network management BENG 4522 Data Communications & Computer Networks

1.2 : Communication tasks • Transmission system utilization • Maximizing the use of transmission facilities that typically shared among numbers of communication device in most efficient way. • Multiplexing for capacity allocation of a transmission medium. • Congestion control to avoid system overwhelming by excessive demand. • Interfacing • Depends on the use of electromagnetic signals propagated over the medium. • Signal generation • Capable of being operated - nature of signal must conform • Interpretable as data at the receiver to the requirements of the transmission system BENG 4522 Data Communications & Computer Networks

1.2 : Communication tasks • synchronization • The art of making clocks tick together. • Timing must be synchronized between the transmitter and the receiver. • Transmission time delay is essential. • Exchange management • Various convention of queuing system, amount and format of data, contingencies methods for error. • Error detection and correction • To guard against loss or damage of data and control information. • Flow control • Function performed by a receiving entity to limit the amount or rate of data that is sent by a transmitting entity, avoid overwhelming the transmission system. BENG 4522 Data Communications & Computer Networks

1.2 : Communication tasks • addressing • Indication of the identity of the transmitter and intended destination. • Routing • Techniques for selecting and maintaining a path through the network. • Recovery • Objective : resume activity at point of interruption or restore to original state. • Message formatting • Agreement between both parties as to the format of data exchanged i.e. in binary converted to characters. BENG 4522 Data Communications & Computer Networks

1.2 : Communication tasks • security • Measure of security to avoid intrusion against the exchange of information over the transmission system. • Network management • Capabilities to configure, monitor, provision and expand the whole network. BENG 4522 Data Communications & Computer Networks

1.3 : Components in data communications of computer network • Protocol • set of rules that manage the data transactions/communications between the devices. • Agreement between the communicating devices - format of data, medium of transmission and speed of transmission etc. BENG 4522 Data Communications & Computer Networks

1.4 : Networking • Physical structure • Types of connection • 2 or more devices connected together through links. • Link is pathway that transfer data from one device to another. BENG 4522 Data Communications & Computer Networks

1.4 : Networking • Point-to-point link BENG 4522 Data Communications & Computer Networks

1.4 : Networking • Multipoint (multidrop) BENG 4522 Data Communications & Computer Networks

1.4 : Networking • Point-to-point communication is not usually practical. • Devices are too far apart. • Large set of devices would need impractical number of connections. • Solutions is a communication network (using multipoint link) • Local Are Network (LAN) • Wide Area Network (WAN) • Metropolitan Area Network (MAN) BENG 4522 Data Communications & Computer Networks

1.4.1 Type of Networks • Categories of networks • Determined by its size, ownership, distance covered, and physical architecture. BENG 4522 Data Communications & Computer Networks

1.4.1.1 Local Area Network (LAN) • Single Building LAN • Usually privately owned and links the devices in a single office, building or campus. BENG 4522 Data Communications & Computer Networks

1.4.1.1 Local Area Network (LAN) • Multiple Building LAN • Size limited to a few kilometers. • Common topologies are bus, ring and star. • High data rate – 4/10/16 Mbps to 100 Mbps or gigabits. BENG 4522 Data Communications & Computer Networks

1.4.1.2 Metropolitan Area Network (MAN) • Extend over entire city, maybe wholly owned by a private company, popular services SMDS. BENG 4522 Data Communications & Computer Networks

1.4.1.3 Wide Area Network (WAN) • Long-distance transmission over large geographical areas (continent/world). • Utilize public, leased or private communication in combinations. • An enterprise network is a WAN owned by one company. BENG 4522 Data Communications & Computer Networks

1.4.1.4 LAN/MAN/WAN Comparison BENG 4522 Data Communications & Computer Networks

1.4.2 Network Topology • The study of location • 2 types of topology • Physical – describes the wiring scheme • Logical – describes how data flows through the network • Network can have different physical and logical topologies • Type of topologies • Fully connected (mesh) • Bus • Ring • Star • Extended star • Tree • Irregular • Cellular • Hybrid BENG 4522 Data Communications & Computer Networks

1.4.2.1 Mesh Topology • Mesh topology • Every node is linked directly to every other node. • Not practical for geographically distributed users. • Redundant connection, should any link fail to function, information can flow through any number of other links to reach its destination. • Very costly (N users require N times (N-1) links !). • Simple, straight forward operation. BENG 4522 Data Communications & Computer Networks

1.4.2.2 Bus Topology • Bus topology • Single cable connects all computers. • Each computer has connector to shared single cable (called as bus or backbone). • Terminators signal the physical end to the segment. • Logical – all devices can see all communications. • Physical – each device is on the same wire. BENG 4522 Data Communications & Computer Networks

1.4.2.2 Bus Topology • Advantages • Works well for small networks. • Relatively inexpensive to implement. • Easy to add to it. • Disadvantages • Management costs can be high. • Potential for congestion with network traffic. • Breakdown in the bus cable brings the entire network down. BENG 4522 Data Communications & Computer Networks

1.4.2.3 Ring Topology • Ring topology • Computers connected in cascading order to make a closed loop ring. • The source station transfers the information to the next station on the ring, which checks the address of the information. • Continuous path for data with no logical beginning or ending point, and thus no terminators. • Logical – each station passes data to the adjacent station. • Physical – devices wired in a daisy chain. BENG 4522 Data Communications & Computer Networks

1.4.2.3 Ring Topology • Advantages • Easier to manage, easier to locate a defective node or cable problem. • Well-suited for long distance on a LAN. • Handles high volume network traffic. • Enables reliable communication. • Disadvantages • Expensive (complex hardware with expensive NIC) • Requires more cable and network equipment at the start. • If a link or station breaks down, the entire network is disabled. • Adding new client disrupts the entire network. BENG 4522 Data Communications & Computer Networks

1.4.2.4 Star Topology • Star Topology • Oldest and most common network design. • Multiple nodes attached to a central hub. • Physical – all nodes connected to a center node. • Logical – all data passed through the center node. BENG 4522 Data Communications & Computer Networks

1.4.2.4 Star Topology • Advantages • Easy to design and install. • Low startup costs and easy to manage and maintain. • Layout is easy to modify and troubleshoot . • Reliable. • Easily scalable (easy to add hosts. • Disadvantages • Hub is a single point of failure. • Requires more cabling than the bus. BENG 4522 Data Communications & Computer Networks

1.4.2.5 Extended-Star Topology • E-star topology • An extended star topology repeats a star topology, where each node that links to the center node, is also the center of another star. BENG 4522 Data Communications & Computer Networks

1.4.2.6 Tree & Irregular Topologies • Tree Topologies • Similar to the extended star topology, the primary difference being that it does not use one central node. Instead, it uses a trunk node from which it, then, branches to other nodes. • Ex : telephone networks • Irregular Topologies • There is no obvious pattern to the links and nodes. The wiring is inconsistent; the nodes have varying numbers of wires leading from them. BENG 4522 Data Communications & Computer Networks

1.4.2.7 Cellular Topologies • Cellular Topologies • Consists of circular or hexagonal areas, each of which has an individual node at its center. • Used in wireless cellular networks. BENG 4522 Data Communications & Computer Networks

1.4.2.8 Hybrid Topologies BENG 4522 Data Communications & Computer Networks

1.4.3 Topology-Design Related Issues • Cost of installation and maintenance • Redundancy • Reliability (no single point of failure) • Expandability (scalability) • Need for switching • Process of directing traffic through the network based on a pre-defined route. • Need for routing • Process of finding the best route for the traffic. • Delay BENG 4522 Data Communications & Computer Networks

1.4.4 Network Model • Model – functions and service provided by the network BENG 4522 Data Communications & Computer Networks

1.4.4.1 Peer-to-Peer Network • Peer-to-peer network • There are no dedicated servers or hierarchy among the computers. • All the computers are equal and therefore known as peers. • Each computer serves as client/server and there is no one assigned to be an administrator responsible for the entire network. BENG 4522 Data Communications & Computer Networks

1.4.4.2 Client/Server Network • Client/Server Network • A small number of computers are designated as centralized servers and given the task of providing services to a large number of user machines called clients. • Servers are usually a powerful computers with a lot of memory and storage space, and fast network connections. • Server software runs on server hardware and client software is used on client computers that connected to those servers. • Most of the interaction on the network is between client and server, and not between clients. • Server software is designed to efficiently respond to requests, while client software provides the interface to the human users of the network. BENG 4522 Data Communications & Computer Networks

1.4.4.2 Client/Server Network • Client/Server Network BENG 4522 Data Communications & Computer Networks

Technologies Ethernet Fast Ethernet Token Ring FDDI ATM DQDB X.25 Frame Delay IP-Packet Switching ISDN xDSL etc 1.5 Networking Technology • Applications • Hypertext Transfer Protocol (HTTP)-WWW • File Transfer Protocol (FTP) • Supervisory Control and Data Acquisition (SCADA) • Network Monitoring System (NMS) • Terminal Access – Telnet • E-learning • E-commerce • etc BENG 4522 Data Communications & Computer Networks

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