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III Year B. Tech. CSE – II Sem L T/P/D C 4 1/- / - 3
(R15A0513) Computer Networks
Objectives : To introduce the fundamental types of computer networks. To demonstrate the TCP/IP & OSI model merits & demerits. To know the role of various protocols in Networking UNIT - I: Introduction: Network, Uses of Networks, Types of Networks, Reference Models: TCP/IP Model, The OSI Model, Comparison of the OSI and TCP/IP reference model. Architecture of Internet. Physical Layer: Guided transmission media, Wireless transmission media, Switching UNIT - II: Data Link Layer - Design issues, Error Detection & Correction, Elementary Data Link Layer Protocols, Sliding window protocols Multiple Access Protocols - ALOHA, CSMA,CSMA/CD, CSMA/CA, Collision free protocols, Ethernet- Physical Layer, Ethernet Mac Sub layer, Data link layer switching: Use of bridges, learning bridges, spanning tree bridges, repeaters, hubs, bridges, switches, routers and gateways. UNIT - III: Network Layer: Network Layer Design issues, store and forward packet switching connection less and connection oriented networks-routing algorithms-optimality principle, shortest path, flooding, Distance Vector Routing, Count to Infinity Problem, Link State Routing, Path Vector Routing, Hierarchical Routing; Congestion control algorithms, IP addresses, CIDR, Subnetting, SuperNetting, IPv4, Packet Fragmentation, IPv6 Protocol, Transition from IPv4 to IPv6, ARP, RARP. UNIT - IV: Transport Layer: Services provided to the upper layers elements of transport protocol addressing connection establishment, Connection release, Error Control & Flow Control, Crash Recovery. The Internet Transport Protocols: UDP, Introduction to TCP, The TCP Service Model, The TCP Segment Header, The Connection Establishment, The TCP Connection Release, The TCP Sliding Window, The TCP Congestion Control Algorithm. UNIT - V: Application Layer- Introduction, providing services, Applications layer paradigms: Client server model, HTTP, E-mail, WWW, TELNET, DNS; RSA algorithm, TEXT BOOKS:
- Computer Networks - Andrew S Tanenbaum, 4th Edition, Pearson Education.
- Data Communications and Networking - Behrouz A. Forouzan, Fifth Edition TMH, 2013.
REFERENCES BOOKS:
- An Engineering Approach to Computer Networks - S. Keshav, 2nd Edition, Pearson Education.
- Understanding communications and Networks, 3rd Edition, W. A. Shay, Cengage Learning.
- Computer Networking: A Top-Down Approach Featuring the Internet, James F. Kurose, K. W. Ross, 3rd Edition, Pearson Education. Outcomes: Students should be understand and explore the basics of Computer Networks and Various Protocols. Student will be in a position to understand the World Wide Web concepts. Students will be in a position to administrate a network and flow of information further Student can understand easily the concepts of network security, Mobile
UNIT - I
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. “Computer network’’ to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. Networks come in many sizes, shapes and forms, as we will see later. They are usually connected together to make larger networks, with the Internet being the most well-known example of a network of networks. There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent system. Usually, it has a single model or paradigm that it presents to the users. Often a layer of software on top of the operating system, called middleware , is responsible for implementing this model. A well-known example of a distributed system is the World Wide Web. It runs on top of the Internet and presents a model in which everything looks like a document (Web page). USES OF COMPUTER NETWORKS
1. Business Applications to distribute information throughout the company ( resource sharing). sharing physical resources such as printers, and tape backup systems, is sharing information client-server model. It is widely used and forms the basis of much network usage. communication medium among employees. email ( electronic mail ), which employees generally use for a great deal of daily communication. Telephone calls between employees may be carried by the computer network instead of by the phone company. This technology is called IP telephony or Voice over IP ( VoIP ) when Internet technology is used. Desktop sharing lets remote workers see and interact with a graphical computer screen doing business electronically, especially with customers and suppliers. This new model is called e-commerce ( electronic commerce ) and it has grown rapidly in recent years. 2 Home Applications peer-to-peer communication person-to-person communication
BOTNET ATTACK: Botnets can be used to perform distributed denial-of-service attack (DDoS attack), steal data, send spam, and allows the attacker to access the device and its connection. The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness, and jitter. I. Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. 2 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 a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.
- Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result. A data communications system has five components I. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2 Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.
- Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
- Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
- Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese. Data Representation
Text Numbers Images Audio Video Data Flow Communication between two devices can be simplex, half-duplex, or full-duplex as shown in Figure. Simplex In simplex mode, the communication is unidirectional, as on a one- way street. Only one of the two devices on a link can transmit; the other can only receive (Figure a). Keyboards and traditional monitors are examples of simplex devices. Half-Duplex In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa (Figure b). Walkie-talkies and CB (citizens band) radios are both half- duplex systems. Full-Duplex In full-duplex, both stations can transmit and receive simultaneously (Figure c). One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time. Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. Performance Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another. Response time is the elapsed time between
Physical Topology The term physical topology refers to the way in which a network is laid out physically. Two or more devices connect to a link; two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. There are four basic topologies possible: mesh, star, bus, and ring MESH: A mesh topology is the one where every node is connected to every other node in the network. A mesh topology can be a full mesh topology or a partially connected mesh topology. In a full mesh topology , every computer in the network has a connection to each of the other computers in that network. The number of connections in this
network can be calculated using the following formula ( n is the number of computers in the network): n(n-1)/ In a partially connected mesh topology , at least two of the computers in the network have connections to multiple other computers in that network. It is an inexpensive way to implement redundancy in a network. In the event that one of the primary computers or connections in the network fails, the rest of the network continues to operate normally. Advantages of a mesh topology Can handle high amounts of traffic, because multiple devices can transmit data simultaneously. A failure of one device does not cause a break in the network or transmission of data. Adding additional devices does not disrupt data transmission between other devices. Disadvantages of a mesh topology The cost to implement is higher than other network topologies, making it a less desirable option. Building and maintaining the topology is difficult and time consuming. The chance of redundant connections is high, which adds to the high costs and potential for reduced efficiency. STAR: A star network , star topology is one of the most common network setups. In this configuration, every node connects to a central network device, like a hub, switch, or computer. The central network device acts as a server and the peripheral devices act as clients. Depending on the type of network card used in each computer of the star topology, a coaxial cable or a RJ-45 network cable is used to connect computers together. Advantages of star topology Centralized management of the network, through the use of the central computer, hub, or switch. Easy to add another computer to the network. If one computer on the network fails, the rest of the network continues to function normally. The star topology is used in local-area networks (LANs), High-speed LANs often use a star topology with a central hub. Disadvantages of star topology
A ring topology is a network configuration in which device connections create a circular data path. In a ring network, packets of data travel from one device to the next until they reach their destination. Most ring topologies allow packets to travel only in one direction, called a unidirectional ring network. Others permit data to move in either direction, called bidirectional. The major disadvantage of a ring topology is that if any individual connection in the ring is broken, the entire network is affected. Ring topologies may be used in either local area networks (LANs) or wide area networks (WANs). Advantages of ring topology All data flows in one direction, reducing the chance of packet collisions. A network server is not needed to control network connectivity between each workstation. Data can transfer between workstations at high speeds. Additional workstations can be added without impacting performance of the network. Disadvantages of ring topology All data being transferred over the network must pass through each workstation on the network, which can make it slower than a star topology. The entire network will be impacted if one workstation shuts down. The hardware needed to connect each workstation to the network is more expensive than Ethernet cards and hubs/switches. Hybrid Topology A network can be hybrid. For example, we can have a main star topology with each branch connecting several stations in a bus topology as shown in Figure Types of Network based on size The types of network are classified based upon the size, the area it covers and its physical architecture. The three primary network categories are LAN, WAN and MAN. Each network differs in their characteristics such as distance, transmission speed, cables and cost. Basic types
LAN (Local Area Network) Group of interconnected computers within a small area. (room, building, campus) Two or more pc's can from a LAN to share files, folders, printers, applications and other devices. Coaxial or CAT 5 cables are normally used for connections. Due to short distances, errors and noise are minimum. Data transfer rate is 10 to 100 mbps. Example: A computer lab in a school. MAN (Metropolitan Area Network) Design to extend over a large area. Connecting number of LAN's to form larger network, so that resources can be shared. Networks can be up to 5 to 50 km. Owned by organization or individual. Data transfer rate is low compare to LAN. Example: Organization with different branches located in the city. WAN (Wide Area Network) Are country and worldwide network. Contains multiple LAN's and MAN's. Distinguished in terms of geographical range. Uses satellites and microwave relays. Data transfer rate depends upon the ISP provider and varies over the location. Best example is the internet. Other types WLAN (Wireless LAN) A LAN that uses high frequency radio waves for communication. Provides short range connectivity with high speed data transmission. PAN (Personal Area Network) Network organized by the individual user for its personal use. SAN (Storage Area Network) Connects servers to data storage devices via fiber-optic cables. E.g.: Used for daily backup of organization or a mirror copy A transmission medium can be broadly defined as anything that can carry information from a source to a destination.
Applications Twisted-pair cables are used in telephone lines to provide voice and data channels. Local-area networks, such as l0Base-T and l00Base-T, also use twisted-pair cables. Coaxial Cable Coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted pair cable. coax has a central core conductor of solid or stranded wire (usuallycopper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two. The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit.This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover. The most common type of connector used today is the Bayone-Neill-Concelman (BNe), connector. Applications Coaxial cable was widely used in analog telephone networks,digital telephone networks Cable TV networks also use coaxial cables. Another common application of coaxial cable is in traditional Ethernet LANs Fiber-Optic Cable A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance suddenly enters another substance(of a different density), the ray changes direction. Bending of light ray
Optical fibers use reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic. Propagation Modes Multimode is so named because multiple beams from a light source move through the core in different paths. How these beams move within the cable depends on the structure of the core, as shown in Figure. In multimode step-index fiber , the density of the core remains constant from the center to the edges. A beam of light moves through this constant density in a straight line until it reaches the interface of the core and the cladding. The term step index refers to the suddenness of this change, which contributes to the distortion of the signal as it passes through the fiber. A second type of fiber, called multimode graded-index fiber , decreases this distortion of the signal through the cable. The word index here refers to the index of refraction. Single-Mode: Single-mode uses step-index fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal.
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Radio Waves Microwaves Infrared Unguided signals can travel from the source to destination in several ways: ground propagation, sky propagation, and line-of-sight propagation, as shown in Figure Radio Waves Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves. Radio waves are omni directional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna sends waves that can be received by any receiving antenna. The omni directional property has a disadvantage, too. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signals using the same frequency or band. Omni directional Antenna Radio waves use omnidirectional antennas that send out signals in all directions. Based on the wavelength, strength, and the purpose of transmission, we can have several types of antennas. Figure shows an omnidirectional antenna.
Applications The Omni directional characteristics of radio waves make them useful for multicasting, in which there is one sender but many receivers. AM and FM radio, television, maritime radio, cordless phones, and paging are examples of multicasting. Microwaves Electromagnetic waves having frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. The sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas Unidirectional Antenna Microwaves need unidirectional antennas that send out signals in one direction. Two types of antennas are used for microwave communications: the parabolic dish and the horn Applications: Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs Infrared Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm), can be used for short-range communication. Infrared waves, having high frequencies, cannot penetrate walls. This advantageous
