Data Communication PDF

SYLLABUS MODULE I Introduction to data communication – definition, components, data representations, data flow. Networks – definition, network criteria, types of connection, physical topology, network types, Internet. TCP/IP and OSI models- functions of layers in both models, comparison, TCP...

SYLLABUS MODULE I Introduction to data communication – definition, components, data representations, data flow. Networks – definition, network criteria, types of connection, physical topology, network types, Internet. TCP/IP and OSI models- functions of layers in both models, comparison, TCP/IP protocol suite. DATA COMMUNICATION Data Communication is the transfer of data from source to receiver(s) through any communication medium based on a set of rules, called protocol. Data Communication Components (Elements of a data communication system) The basic components (elements) of a data communication system consists of o Message o Sender / Transmitter o Receiver o Transmission medium o Protocol. Message: It is the data or information to be transferred from one device to another across a computer network. Sender: Sender is the device that sends data over a network. It can be computer, mobile handset, video camera etc. Receiver: A receiver is the device that receives the data from the network. Transmission media: It is the communication channel that carries information from sender to receiver. Eg: - wires, cables, radio waves etc. Protocol: A protocol is a set of rules to be followed by both sender and receiver. 1 DATA REPRESENTATION FORMS The information to be transmitted from a sender to the receiver comes in different forms such as text, numbers, images, audio, video etc. Text: ▪ Text is represented as a bit pattern, a sequence of bits (0s or 1s). ▪ Different sets of bit patterns are used to represent a text. ▪ Each sets of bits is called a code and the process of representing symbols is called coding. Unicode: This coding system uses 32 bits to represent a symbol. ASCII: The American Standard Code for Information Interchange (ASCII) constitutes the first 127 characters in the Unicode. Numbers: ▪ Numbers are represented by bit patterns. ▪ The number is directly converted to a binary number to simplify mathematical operations. Images: ▪ Images are represented by bit patterns. ▪ 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. ▪ Better resolution: better representation of image ▪ More memory needed to store the better image Audio: ▪ Audio refers to the recording or broadcasting of sound or music. ▪ It is continuous signals. ▪ These types of information are converted to digital or analog signals before transmission. Video: ▪ Video refers to the recording of a picture or movie. ▪ Video can either be produced as a continuous entity (Ex. By a TV camera) or as a combination of images, arranged to convey the idea of motion. 2 Data Flow methods: Data flow methods or Transmission Mode defines the direction of the flow of information between two communication devices. Three ways or modes of data transmission: ▪ Simplex ▪ Half duplex (HDX) ▪ Full duplex (FDX) Simplex Mode: ▪ In simplex mode, the communication is unidirectional (one way). ▪ Only one of the two devices on a link can transmit; the other can only receive. ▪ In this, message cannot be sent back to the sender. ▪ Simplex mode can use entire capacity of the channel to send data in one direction ▪ Ex: Keyboards and traditional Monitors Half-Duplex Mode: o Bidirectional o Each station can both transmit and receive, but not at the same time. o When one device is sending, the other can only receive, and vice versa. o The entire capacity of the channel can be utilized for each direction. o Example: walkie-talkie 3  Full-Duplex Mode: o Bidirectional o In full duplex mode (also called duplex), both stations can transmit and receive simultaneously. o Example: Telephone Network o Data signals going in each direction share the capacity of the link with signals going in the other direction. o Sharing can be implemented in two ways. The link may contain two physically separate transmission paths. The capacity of the channel is divided between signals travelling in both directions. **************************************************************************** Computer Network ▪ A computer network is a group of computing devices connected with each other through a transmission medium such as wires, cables, radio waves etc. ▪ Each device in a computer network is called as nodes ▪ The purpose of having computer network is to exchange information over the network. Network Criteria/Attributes Performance o Performance is the measure of service quality of a network. o The performance of a network can be measured in terms of the following factors. Response time: o Elapsed time between an inquiry and a response. Transit time: o Amount of time required for a message to travel from one device to another Delay o Network delay refers to the time taken for a packet to go from source to destination. 4  Throughput o Throughput refers to the amount of successful packet delivery within a specified amount of time. Packet Loss o When one or more packets fails to reach its intended destination, this is called packet loss. Reliability ▪ It is measured by the o frequency of failure o the time it takes a link to recover from a failure o and the network's robustness. Security ▪ Network security issues include o protecting data from unauthorized access o protecting data from damage and development, o implementing policies and procedures for recovery from breaches and data losses. Distributed Processing: ▪ Most networks use distributed processing, in which a task is divided among multiple computers. Type of Connection: ▪ There are two possible types of connections: point-to-point multipoint Point-to-Point A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those twodevices. 5  Multipoint In a multipoint connection, single communication channel is shared by multiple devices. Physical Topology: ▪ Physical topology refers to the structure of the network ▪ The topology of a network is the geometric representation of all the links and linking devices (usually called nodes) to one another. ▪ The four basic topologies are Bus, Star, Ring and Mesh. ***************************************************************************** TOPOLOGY ▪ Topology refers to the structure of the network ▪ It defines the way in which all components in the network are interconnected. ▪ The different topologies are mesh, star, bus, ring, tree and hybrid MESH TOPOLOGY Every node in the network has a dedicated point-to-point link to every other node. Each link carries information only between the two devices that it connects. The Internet is an example of the mesh topology. 6 Advantages Robust. Fault is diagnosed easily. Reliable data transfer. Provides security and privacy. Disadvantages Installation and configuration is difficult. Cost of cables are high Cost of maintenance is high. STAR TOPOLOGY Each device is connected to a hub through a dedicated point-to-point link. The devices are not directly linked to each other. If one device wants to send data to another, it sends it first to the hub,which then forwards the data to the other connected device. Advantages If N devices are connected to each other in star topology, then the number of cables required to connect them is N. So, it is easy to set up. Less expensive than mesh Easy to configure If one link fails the network can still function Disadvantages If the hub fails, the wholesystem will crash down. Cost of installation is high. Performance is based on hub. BUS TOPOLOGY All devices are connected to a single communication line or cable. This cable acts as a backbone for the entire network. When a node wants to send a message to other node, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not. 7 Advantages Easy to install Low cost Cable Disadvantages Difficult to reconfigure Difficult to troubleshoot RING TOPOLOGY Every device has a dedicated point-to-point connection with only the two devices on either side of it. The data flows in one direction, i.e., it is unidirectional. Advantages Easy to install Easy to reconfigure Easy to detect a problem Disadvantages If a node fails, the whole network will fail. 8  Slow data transmission speed (each message has to go through the ring path). Difficult to reconfigure (we have to break the ring). Tree Topology Tree topology combines the characteristics of bus topology and star topology. All the computers are connected with each other in hierarchical fashion. The top-most node in tree topology is known as a root node Advantages: Easy to expand. Easy to maintain and manage. Easy to detect error. Disadvantages: Heavily cabled topology Expensive when compared to other topologies. If the root node collapses, the network will also collapse. Hybrid Topology A Hybrid Topology is a network topology comprising two or more different types of topologies. It is a reliable and scalable topology, but it is a costly one. It has the merits and demerits of the topologies used to build it. 9 Advantages Easy to troubleshoot and provides simple error-detecting techniques. Flexible. Scalable. Drawbacks Not easy to design. Costly. ***************************************************************************** Type of Network Connection There are two possible types of connections: point-to-point multipoint Point-to-Point A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Most point-to-point connections a r e wired/cabled, but microwave or satellite links are also possible. 10 Multipoint In a multipoint connection, single communication channel is shared by multiple devices. So, it can be said that the channel capacity is shared temporarily by every device connecting to the link. Comparisons Point to Point Multipoint There is dedicated link between two The link is shared between more than two devices. devices. The channel's entire capacity is reserved The channel's capacity is shared among for the two devices. multiple devices There is a single transmitter and a single There is a single transmitter and multiple receiver. receivers. Provides security and privacy because Does not provide security and privacy communication channel is not shared. because communication channel is shared. ***************************************************************************** Network categories o A computer network is a group of computers connected with each other through a transmission medium such as cable, wire etc o There are mainly three types of computer networks based on their size o Local Area Network (LAN) o Metropolitan Area Network (MAN) o Wide area network (WAN) Local Area Network (LAN) o A Local Area Network (LAN) is a group of connected devices that are in a limited area such as a school, office, building, or home. o LAN is mostly used for sharing hardware resources such as printers, files, scanners, etc. 11  o LANs can be wired type and wireless type o Advantages o LANs due to their small size it is faster, their speed can range from 100 to 1000Mbps. o Easy to set up o Relatively inexpensive hardware o LAN is secure because there is no outside connection with the local area network thus the data which is shared is safe on the local area network and can’t be accessed outside. o Disadvantages o Need constant administration of experienced engineers for functioning. Metropolitan Area Network (MAN) o The size of the Metropolitan Area Network is larger than LANs and smaller than WANs (Wide Area Networks) o It connects two or more computers that are apart but resides in the same or different cities. o Examples: Cable TV network in a city. 12  o MAN is designed for customers who need a high-speed connectivity. o Advantages: o Provides high-speed connectivity over a larger geographical area than LAN. o Can be used as an ISP for multiple customers. o Offers higher data transfer rates than WAN in some cases. o Disadvantages: o Can be expensive to set up and maintain. o May experience congestion and network performance issues with increased usage. o May have limited fault tolerance and security compared to LANs. Wide Area Network (WAN) o Wide area network provides long distance transmission of data. o A WAN can cover country, continent or even a whole world. o Internet connection is an example of WAN. o Other examples of WAN are mobile broadband connections such as 3G, 4G etc. o The WAN network can be made up of multiple LAN and MAN networks. o Advantages of WAN: ▪ Covers large geographical areas and is used for large-distance connections and can connect remote locations. ▪ Offers remote access to resources and applications. ▪ Can be used to support multiple users and applications simultaneously. 13 o Disadvantages of WAN: ▪ High probability of attack from hackers and cybercriminals due to large networks. ▪ Offers slower data transfer rates than LAN or MAN. ▪ It is difficult to prevent hacking and debug a large network. ▪ High cost to set up the network and the Support of experienced technicians is needed to maintain the network Basis of LAN MAN WAN Comparison Full Form Local Area Metropolitan Wide Area Network. Area Network. Network. Geographical 1 km to 10 km 10 km to 100 Beyond 100 km Area km Ownership of Private. Private or Private or Network Public. Public. Speed High Average Low Maintenance Easy to design and Difficult to Difficult to and Design maintain. maintain. maintain. Operational Usually 10, 100 and usually is 1.5 usually is 100 Speed 1000 Mbps. Mbps Mbps. Fault Tolerance High tolerance Low tolerance Low tolerance Communication Small number of Simultaneous Large number Allotment computers to communication of computers to establish a of a large interact communication. number of simultaneously computers. with each other 14  Congestion Network congestion Network Network is very is very low due to congestion is high. less number of high. computers Propagation propagation delay is propagation propagation Delay very less. delay is delay is very moderate. high. Examples Computer networks Computer Computer of schools, homes, networks that networks that offices, hospitals, spread over a cover an entire etc. are the common small city, or city, or globe examples of LANs. town are the like internet are examples of the examples MANs. WANs. ******************************************************************* Inter connection of networks (Internet) o The internet is a global network of interconnected computers, servers, phones, and smart appliances. o It uses the transmission control protocol (TCP) standard to enable the fast exchange of information and files. o The internet provides a vast array of information and services, including: o The World Wide Web (WWW) o Email o File sharing o Online communication o Millions of people are users **************************************************************************** OSI/ISO Reference Model 15 Application Layer The application layer interacts with application programs This layer is responsible for user interface specifications. It provides protocols that allow data communication Eg: Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP) etc… Functions of Application layer: o File transfer, access, and management (FTAM): Allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. o Mail services: Provides the facility for email forwarding and storage. o Directory services: Provides the distributed database sources and is used to provide that global information about various objects. Presentation Layer A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems. Functions of Presentation layer: o Translation: o Converts the data from sender-dependent format into a common format at the transmission end o Changes the common format into receiver-dependent format at the receiving end. o Encryption: 16  o Encryption is needed to maintain privacy. o Encryption is a process of converting the sender-transmitted information into another form o Compression: o Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Session Layer The session layer creates communication channels, called sessions, between devices. Functions of Session layer: o Dialog control: ▪ Determines which device will communicate first and the amount of data that will be sent. o Synchronization: ▪ Session layer adds some checkpoints when transmitting the data in a sequence. ▪ If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. Transport Layer This layer is responsible for process-to-process communication and error-free delivery of data. Two main protocols in this layer are TCP and UDP. UDP and TCP are responsible for delivery of a message from a process to another process. Functions of Transport Layer: o Service-point addressing: o Adds port address to the header of the message o Segmentation and reassembly: o Divides the message received from upper layer into multiple segments o At the destination, reassembles the message. o Connection control: o Transport layer provides two services o Connection-oriented service: o Makes a logical connection between processing before delivering packets o All the packets travel in the single route. o Connectionless service: o No logical connection establishment o Packets may not travel in same route o Flow control: o Responsible for sending data at a rate that matches with the speed of the receiver o Error control: o Ensures that message reach at the destination process without any error. Network Layer 17  The main responsibility of the network layer is the transport of packets from source to destination across the network. Functions of Network Layer: o Internetworking: o It provides logical connection between different types of networks. o Addressing: o Used to identify the device on the internet. o The sender & receiver’s IP addresses are placed in the header of the message o Routing: o Determines the best optimal path out of the multiple paths from source to the destination. Data Link Layer The data link layer is responsible for error free the node-to-node delivery of the message. Functions of the Data-link layer o Framing: ▪ The data link layer translates the data bit stream into Frames. o Physical Addressing: ▪ After creating frames, the Data link layer adds physical addresses (MAC addresses) of the sender and/or receiver in the header of each frame. o Flow Control: ▪ Flow control is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. o It ensures that the sender sends data at a rate that matches with the speed of the receiver o Error Control: ▪ Ensures that message reach at the destination node without any error. o Access Control: ▪ When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time. It contains two sub-layers: o Logical Link Control Layer ▪ It is responsible for identifying network protocols, performs error checking and flow control o Media Access Control Layer ▪ It is used for transferring the packets over the network. ▪ Uses MAC addresses to connect devices and define permissions to transmit and receive data. Physical Layer The physical layer is responsible for physically transmitting individual data bits from one node to the next. Functions of a Physical layer: 18  o Line Configuration: It defines how two or more devices can be connected physically. o Data Transmission: It defines the transmission mode whether it is simplex, half- duplex or full-duplex mode between the two devices on the network. o Topology: It defines the way how network devices are arranged. o Signals: It determines the type of the signal used for transmitting the information. o Bit rate control: The Physical layer also defines the transmission rate i.e. the number of bits sent per second. ***************************************************************************** TCP/ IP ARCHITECTURE TCP/IP stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model contains four layers The layers are: ▪ Application Layer ▪ Transport Layer ▪ Internet Layer ▪ Network Access/Link Layer TCP/IP PROTOCOL SUITE 19 Application Layer The application layer interacts with application programs This layer is responsible for user interface specifications. It provides protocols that allow data communication Many protocols are defined such as HTTP, HTTPS, FTP, TFTP,Telnet, SSH, SMTP, SNMP etc… Transport Layer This layer is responsible for process-to-process communication and error-free delivery of data. Two main protocols in this layer are TCP and UDP. UDP and TCP are responsible for delivery of a message from a process to another process. 20  Transmission Control Protocol o The Transmission Control Protocol (TCP) is a reliable connection- oriented protocol o A logical connection must be established between sender and receiver before data transmission. o It provides reliable communication and error free delivery of data from source to destination User Datagram Protocol o The User Datagram Protocol (UDP) is a connectionless transport layer protocol. o It provides simple, cost-effective but unreliable service. o It prioritizes speed over the accuracy of delivery. Stream Control Transmission Protocol o The Stream Control Transmission Protocol (SCTP) provides supportfor newer applications such as voice over the Internet. o It is a transport layer protocol that combines the best features of UDPand TCP. Internet/Network Layer The main responsibility of the internet layer is the transport of packets from source to destination across the network. At this layer, TCP/IP supports the Internetworking Protocol (IP). IP, in turn, uses four supporting protocols: ARP, RARP, ICMP, and IGMP. Internetworking Protocol (IP) o The Internetworking Protocol (IP) is the protocol used for sending data from source to destination. 21  o The main task of IP is to deliver the packets from source to the destination based on the IP addresses available in the packet headers. Address Resolution Protocol (ARP) o The Address Resolution Protocol (ARP) is used t o find the MAC (Media Access Control) address of a device from its IP address. Reverse Address Resolution Protocol (RARP) o The Reverse Address Resolution Protocol (RARP) allows a host to discover its Internet address when it knows only its physical address. o It is used when a computer is connected to a network for the first timeor when a diskless computer is booted. Internet Control Message Protocol (ICMP) o The Internet Control Message Protocol (ICMP) is a mechanism used to send control messages to network devices and hosts. o ICMP sends query and error reporting messages. Internet Group Message Protocol (IGMP) o The Internet Group Message Protocol (IGMP) is used to facilitate the simultaneous transmission of a message to a group of recipients. Network Access/Link Layers This layer is a combination of physical and data link layer in the OSI model. It defines how the data is physically through a network. At the physical and data link layers, TCP/IP does not define any specificprotocol. It supports all the standard and proprietary protocols. ********************************************************************* **************************************************************************** 22  OSI Model TCP/IP Model It stands for Open System Interconnection. It stands for Transmission Control Protocol. OSI model has been developed by ISO It was developed by ARPANET (Advanced (International Standard Organization). Research Project Agency Network). It is an independent standard and generic It consists of standard protocols that lead to the protocol used as a communication gateway development of an internet. It is a between the network and the end user. communication protocol that provides the connection among the hosts. In the OSI model, the transport layer provides The transport layer does not provide the surety a guarantee for the delivery of the packets. for the delivery of packets. But still, we can say that it is a reliable model. This model is based on a vertical approach. This model is based on a horizontal approach. In this model, the session and presentation In this model, the session and presentation layer layers are separated, i.e., both the layers are are not different layers. Both layers are included different. in the application layer. In this model, the network layer provides both The network layer provides only connectionless connection-oriented and connectionless service. service. Protocols in the OSI model are hidden and In this model, the protocol cannot be easily can be easily replaced when the technology replaced. changes. It consists of 7 layers. It consists of 4 layers. OSI model defines the services, protocols, In the TCP/IP model, services, protocols, and and interfaces as well as provides a proper interfaces are not properly separated. It is distinction between them. It is protocol protocol dependent. independent. The usage of this model is very low. This model is highly used. Sample Questions 1. Illustrate TCP/IP protocol suite 2. Explain with neat diagram, OSI reference model 3. Explain physical topologies with their advantages & disadvantages 23  4. Compare & Contrast OSI model & TCP/IP model 5. Describe the different network attributes 6. Illustrate Network categories 7. Explain data transmission modes based on direction of data flow. 3 Marks 1. Illustrate the elements of data communication 2. Explain different methods of representing data 3. Differentiate point to point & multipoint connections 4. Explain Inter connection of networks or Internet 1 Mark 1. Define data communication 2. Define Computer Network 3. List the different physical topologies 4. Differentiate between transit time & delay 5. List the three data flow methods 24