Unit 1.pdf

CAP476: Data Communiction and Networking Unit-I: Data Communications School of Computer Applications Lovely Professional University Computer Networks A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by co...

CAP476: Data Communiction and Networking Unit-I: Data Communications School of Computer Applications Lovely Professional University Computer Networks A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices. Data Communication  Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it.  The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver.  Actual Data Communication is referred to the transfer of data, the method of transfer and the preservation of the data during the transfer process. Effectiveness of Data Communication The effectiveness of a data communication system depends on the three fundamental characteristics: 1. 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 data accurately. Data that have been altered in transmission and left uncorrected are rustles 3. Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video, audio, and voice data, 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 id called real-time transmission. Components of Data Communication System The following are the basic requirements for working of a communication system. 1. The sender (source) who creates the message to be transmitted 2. A medium that carries the message 3. The receiver (sink) who receives the message 1. Message: A message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form. 2. Sender: The sender will have some kind of meaning she wishes to convey to the receiver. It might not be conscious knowledge, it might be a sub-conscious wish for communication. What is desired to be communicated would be some kind of idea, perception, feeling, or datum. It will be a part of her reality that she wishes to send to somebody else. 3. Receiver: These messages are delivered to another party. Keep in mind, the other party also enters into the communication process with ideas and feelings that will undoubtedly influence their understanding of your message and their response. To be a successful communicator, you should consider these before delivering your message, then acting appropriately. 4. Medium: Medium is a means used to exchange/transmit the message. The sender must choose an appropriate medium for transmitting the message else the message might not be conveyed to the desired recipients. The choice of appropriate medium of communication is essential for making the message effective and correctly interpreted by the recipient. This choice of communication medium varies depending upon the features of communication. 5. Protocol: A protocol is a formal description of digital message formats and the rules for exchanging those messages in or between computing systems and in telecommunications. Protocols may include signalling, authentication and error detection and correction syntax, semantics, and synchronization of communication and may be implemented in hardware or software, or both. 6. Feedback: Feedback is the main component of communication process as it permits the sender to analyse the efficacy of the message. It helps the sender in confirming the correct interpretation of message by the decoder. Feedback may be verbal (through words) or non-verbal (in form of smiles, sighs, etc.). It may take written form also in form of memos, reports, etc. Data Representation Information shared on the networks are of different forms represented by various codes such as ASCII, EBCDIC, BCD etc.  Text: In data communications, text is represented as a bit pattern, a sequence of bits (0s or 1s). Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the process of representing symbols is called coding.  Numbers: Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the number is directly converted to a binary number to simplify mathematical operations.  Images: Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution.  Audio: Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It is continuous, not discrete.  Video: Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion. Transmission Modes (Data Flow) The flow of data on a communications channel between two machines can occur in several different ways known as transmission modes. The data flow or transmission is characterized by following characteristics:  Direction of the exchanges  Transmission: the number of bits sent simultaneously  Synchronization between the transmitter and receiver Simplex  A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions  for example, from your computer to the printer or from the mouse to your computer.  There is no mechanism in for information to be transmitted back from receiver to sender.  The entire capacity of the channel is used to send data in one direction. Half Duplex  A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time.  for example walkie talkie  With this type of connection, each end of the connection transmits in turn.  This type of connection makes it possible to have bidirectional communications using the full capacity of the line. Full Duplex  A full-duplex connection is a connection in which the data flow in both directions simultaneously.  For example communication between two interconnected computers, your mobile phones  Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission. Topology  The term “Topology” refers to the way in which the end points or stations/computer systems, attached to the networks, are interconnected.  A topology is essentially a stable geometric arrangement of computers in a network. If you want to select a topology for doing networking.You have attention to the following points.  Application S/W and protocols  Types of data communicating devices  Geographic scope of the network  Cost  Reliability Types of Topologies Depending on the requirement there are different Topologies to construct a network.  Point-to-Point topology  Bus topology  Star topology  Ring topology  Mesh topology  Tree (Hierarchical) topology  Daisy Chain  Cellular topology  Hybrid Topology Point to Point Topology  Point-to-point networks contains exactly two hosts such as computer, switches or routers, servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa.  If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly. Bus topology  In case of Bus topology, all devices share single communication line or cable.  Bus topology may have problem while multiple hosts sending data at the same time.  Therefore, Bus topology either uses CSMA/CD technology or recognizes one host as Bus Master to solve the issue.  It is one of the simple forms of networking where a failure of a device does not affect the other devices.  But failure of the shared communication line can make all other devices stop functioning.  Both ends of the shared channel have line terminator.  The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from the line. Star topology  All hosts in Star topology are connected to a central device using a point-to-point connection. That is, there exists a point to point connection between hosts and central device. The central device can be any of the following:  Layer-1 device such as hub or repeater  Layer-2 device such as switch or bridge  Layer-3 device such as router or gateway As in Bus topology, hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts, takes place through only the hub. Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple. Ring topology  In ring topology, each host machine connects to exactly two other machines, creating a circular network structure.  When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts.  To connect one more host in the existing structure, the administrator may need only one more extra cable.  Failure of any host results in failure of the whole ring. Thus, every connection in the ring is a point of failure. Mesh topology  In this type of topology, a host is connected to one or multiple hosts.  This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection to few hosts only.  Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to-point links. Mesh technology comes into two types: Full Mesh: All hosts have a point-to-point connection to every other host in the network. Thus for every new host n(n- 1)/2 connections are required. It provides the most reliable network structure among all network topologies. Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all. Tree (Hierarchical) topology  Tree topology also known as Hierarchical Topology, this is the most common form of network topology in use presently.  This topology imitates as extended Star topology and inherits properties of bus topology.  This topology divides the network in to multiple levels/layers of network. Mainly in LANs, a network is bifurcated into three types of network devices.  The lowermost is access-layer where computers are attached.  The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer.  The highest layer is known as core layer, and is central point of the network, i.e. root of the tree from which all nodes fork. Tree (Hierarchical) topology contd…  All neighbouring hosts have point-to-point connection between them.  Similar to the Bus topology, if the root goes down, then the entire network suffers even though it is not the single point of failure. Every connection serves as point of failure, failing of which divides the network into unreachable segment. Daisy Chain  This topology connects all the hosts in a linear fashion. Similar to Ring topology, all hosts are connected to two hosts only, except the end hosts. Means, if the end hosts in daisy chain are connected then it represents Ring topology.  Each link in daisy chain topology represents single point of failure. Every link failure splits the network into two segments.  Every intermediate host works as relay for its immediate hosts. Cellular topology  The cellular topology is applicable only in case of wireless media that does not require cable connection.  In wireless media, each point transmits in a certain geographical area called a cell. Each cell represents a portion of the total network area.  Devices that are in the cell communicate through a central hub. Hubs in different cells are interconnected. They route data across the network and provide a complete network infrastructure.  The data is transmitted in the cellular digital packet data (CDPD) format. Hybrid Topology  A network structure whose design contains more than one topology is said to be hybrid topology. Hybrid topology inherits merits and demerits of all the incorporating topologies. Categories of Networks One way to categorize the different types of computer network designs is by their geographical scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:  PAN – Personal Area Network  LAN - Local Area Network  WLAN - Wireless Local Area Network  WAN - Wide Area Network  MAN - Metropolitan Area Network Personal Area Network  A personal area network is a network concerned with the exchange of information in the vicinity of a person.  Typically, these systems are wireless and involve the transmission of data between devices such as smartphones, personal computers, tablet computers, etc.  The purpose of such a network is usually to allow either transmission of data or information between such devices or to server as the network that allows further up link to the Internet. Local Area Network  A LAN connects network devices over a relatively short distance. LAN is privately owned network that operates in very small geographical area (10 m to a few km) widely used:  To connect personal computers and workstations in offices and factories  To share hardware (like printers, scanners) and software (application software)  To exchange information  A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.  In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.  In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.  LANs are distinguished from one other by three characteristics:  Size of LAN is restricted by number of users licensed to access the operating system or application software  Transmission technology: LAN consists of single type of cable and all the computers/ communicating devices connected to it.  Most local-area networks use a 48-bit physical address  Topology used Wireless Local Area Network (WLAN)  A WLAN, or wireless LAN, is a network that allows devices to connect and communicate wirelessly. Unlike a traditional wired LAN, in which devices communicate over Ethernet cables, devices on aWLAN communicate via Wi-Fi.  While a WLAN may look different than a traditional LAN, it functions the same way. New devices are typically added and configured using DHCP.  They can communicate with other devices on the network the same way they would on a wired network.  The primary difference is how the data is transmitted. In a LAN, data is transmitted over physical cables in a series of Ethernet packets containing. In a WLAN, data is transmitted over the air using one of the IEEE 802.11 protocols.  Many wireless routers also include Ethernet ports, providing connections for a limited number of wireless devices. Metropolitan Area Network  A network spanning a physical area larger than a LAN but smaller than a WAN, such as a city.  A MAN is typically owned an operated by a single entity such as a government body or large corporation. Wide Area Network  A WAN is a network that spans more than one geographical location often connecting separated LANs. A WAN is a geographically-dispersed collection of LANs.  As the term implies, a WAN spans a large physical distance.  The Internet is the largest WAN, spanning the Earth.  A network device called a router connects LANs to aWAN.  In IP networking, the router maintains both a LAN address and a WAN address.  WANs are slower than LANs and often require additional and costly hardware such as routers, dedicated leased lines, and complicated implementation procedures.  A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management.  WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances. Protocol and its Components Protocol is a set of rules that governs data communication. It represents an agreement between the communicating devices. Without protocol two devices may be connected but cannot communicate. The key elements of protocol are: 1. Syntax: The term syntax refers to the structure or format of the data, meaning the order in which they are presented. 2. Semantics: The word semantics refers how a particular pattern to be interpreted and what action is to be taken based on that interpretation. 3. Timing: Timing refers to when the data should be sent and how fast it should be sent? The key functions that a protocol performs are:  Protocol Data Unit: It refers to the breaking of data in manageable units called Protocol Data Unit e.g. Segment, Packet, Frame etc.  Format of packet: Format of the packet like which group of bits in the packet constitute data, address, or control bits.  Sequencing: It refers to the breaking long message into smaller units. Sequencing is responsibility of protocol.  Routing of packets: Finding the most efficient path between source and destination is responsibility of protocol.  Flow control: It is responsibility of the protocol to prevent fast sender to overwhelm slow receiver. It ensures resource sharing and protection against traffic congestion by regulating the flow of data through the shared medium.  Error control: Protocol is responsible to provide method for error detection and correction.  Log related information: Some communication software has features to provide log of usage of network resources.  Defining priority: Different types of packets needs to have different priority while moving on the shared network e.g. network management packets needs to be given higher priority if some congestion occurs.  Creating and terminating a connection: Protocol defines the rules to create and terminate a connection between sender and receiver to communicate among each other.  Security of data: Several communication software has features to prevent data from unauthorized access.