Computer Networks Syllabus PDF

DEPARTMENT OF IT&MCA DVR & Dr. HS MIC COLLEGE OF TECHNOLOGY COMPUTER NETWORKS BY SURESH GORANTLA ASSISTANT PROFESSOR DVR & Dr. HS MIC COLLEGE OF TECHNOLOGY, KANCHIKACHERLA COMPUTER NETWORKS (24MC2T0...

DEPARTMENT OF IT&MCA DVR & Dr. HS MIC COLLEGE OF TECHNOLOGY COMPUTER NETWORKS BY SURESH GORANTLA ASSISTANT PROFESSOR DVR & Dr. HS MIC COLLEGE OF TECHNOLOGY, KANCHIKACHERLA COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 SYLLABUS UNIT-I: Introduction: OSI overview, TCP/IP and other networks models, Examples of Networks: Arpanet, Internet, Network Topologies Wide Area Networks (WAN), Local Area Networks (LAN), Metropolitan Area Networks (MAN). NETWORK  A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications.  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. 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  electronic commerce  entertainment.(game playing,) 3. Mobile Users  Text messaging or texting  Smart phones,  GPS (Global Positioning System)  m-commerce  NFC (Near Field Communication) 4. Social Issues  With the good comes the bad, as this new-found freedom brings with it many unsolved social, political, and ethical issues. MIC- MCA Page 1 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 ADVANTAGES OF NETWORKS  Computers in a networked environment provide numerous advantages when compared to computers in a standalone environment.  The immense benefits that the computer networks provide are in the form of excellent sharing of computational resources, computational load, and increased level of reliability, economy and efficient person-to-person communication. Following are some of the major advantages of using computer networks. 1. Resource Sharing The main aim of a computer network is to make all programs, equipment, and data available to anyone on the network without regard to the physical location of the resource and the user. Users need to share resources other than files, as well. A common example being printers. 2. High Reliability: Computer networks provide high reliability by having alternative sources of supply. For example, all files could be replicated on two or three machines, so, if one of them is unavailable (due to hardware failure), the other copies could be used. 3. Saving Money: Small computers have a much better price/performance ratio than larger ones. Mainframes are roughly a factor of ten faster than personal computers but they cost much more. This imbalance has caused many systems designers to build systems consisting of personal computers, one per user, with data kept on one or more shared file server machines. In this model, the users are called clients, and the whole arrangement is called the client-server model. 4. Scalability: The ability to increase the system performance gradually as the workload grows just by adding more processors. With centralized mainframes, when a system is full, it must be replaced by a larger one, usually at great expense and even greater disruption to the users. 5. Communication Medium: A computer network can provide a powerful communication medium among widely separated users. Using a computer network it is easy for two or more people who are working on the same project and who live far apart to write a report together. When one worker, makes a change to an on-line document, the others can see the change immediately, instead of waiting several days for a letter. Such a speedup makes cooperation among far-flung groups of people easy whereas previously it was impossible. 6. Increased Productivity: Networks increase productivity as several people can enter data at the same time, but they can also evaluate and process the shared data. So, one person can handle accounts receivable, and someone else processes the profit-and-loss statements. NETWORKING MODEL  Most of the networks today are organized as a series of stacked layers with each layer stacked over another layer below it.  This is done in order to divide the workload and to simplify the systems design.  The architecture is considered scalable if it is able to accommodate a number of layers in either large or small scales. For example, a computer that runs an Internet application may require all of the layers that were defined for the architectural model.  Similarly, a computer that acts as a router may not need all these layers.  Systems design is furthermore simplified because with a layered architecture, the design has to only concern the layer in question and not worry about the architecture in a macro sense.  The depth and functionality of this stack differs from network to network.  However, regardless of the differences among all networks, the purpose of each layer is to provide certain services (job responsibilities) to the layer above it, shielding the upper layers from the intricate details of how the services offered are implemented. Every computer in a network possesses within it a generic stack. MIC- MCA Page 2 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  A logical communication may exist between any two computers through the layers of the same “level”.  Layer-n on one computer may converse with layer-n on another computer.  There are rules and conventions used in the communication at any given layers, which are known collectively as the layer-n protocol for the nth layer. Figure: Layered network architecture  Data are not directly transferred from layer-n on one computer to layer-n on another computer.  Rather, each layer passes data and control information to the layer directly below until the lowest layer is reached.  Below layer-1 (the bottom layer), is the physical medium (the hardware) through which the actual transaction takes place.  In Figure logical communication is shown by a broken-line arrow and physical communication by a solid-line arrow. Between every pair of adjacent layers is an interface.  The interface is a specification that determines how the data should be passed between the layers.  It defines what primitive operations and services the lower layer should offer to the upper layer.  One of the most important considerations when designing a network is to design clean-cut interfaces between the layers.  To create such an interface between the layers would require each layer to perform a specific collection of well-understood functions.  A clean-cut interface makes it easier to replace the implementation of one layer with another implementation because all that is required of the new implementation is that, it offers, exactly the same set of services to its neighboring layer above as the old implementation did. MIC- MCA Page 3 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 OSI Reference Model (Open System Interconnection Model)  OSI model defines and used to understand “how Data is transferred from one computer to another in a computer network.”  The Open System Interconnection (OSI) model is a set of protocols that attempt to define and standardize the data communications process; we can say that it is a concept that describes how data communications should take place.  For successful communication between computers, networks or different architectures 7 layer OSI model was introduced by International Standard Organization (ISO) in 1984 and it is now considered the primary architectural model for inter-computer communications.  The OSI model has the support of most major computer and network vendors, many large customers, and most governments in different countries. Layers of OSI reference model: APPLICATIONLAYER PRESENTATIONLAYER SESSIONLAYER TRANSPORTLAYER NETWORK LAYER DATALINKLAYER PHYSICALLAYER Figure: Layers of OSI reference model  The OSI reference model is a conceptual model composed of seven layers as shown in Figure each specifying particular network functions and into these layers are fitted the protocol standards developed by the ISO and other standards bodies.  The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups.  A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently.  This enables the solutions offered by one layer to be updated without affecting the other layers.  The OSI model is modular. Each successive layer of the OSI model works with the one above and below it. Although, each layer of the OSI model provides its own set of functions, it is possible to group the layers into two distinct categories.  The first four layers i.e., physical, data link, network, and transport layer provide the end-to- end services necessary for the transfer of data between two systems.  These layers provide the protocols associated with the communications network used to link two computers together. Together, these are communication oriented.  The top three layers i.e., the application, presentation, and session layers provide the application services required for the exchange of information. MIC- MCA Page 4 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  That is, they allow two applications, each running on a different node of the network to interact with each other through the services provided by their respective operating systems. Together, these are data processing oriented. Layer7—Applicationlayer Layer6—Presentationlayer Layer5—Sessionlayer Layer4—Transport layer Layer3—Networklayer Layer2—DataLink layer Layer1—Physicallayer Layer 7: Application layer  Application layer is the 7th Layer of OSI Model  Here, users directly interact with software to provide the data, which has to be transferred over the network.  Application layer used by network application.  Network application means computer applications use internet like Google chrome, Firefox, outlook, Skype, etc…  Web browser is a network application running in your pc use application layer protocols like HTTP/HTTPS. “Application layers provide services for network applications with help of protocols to perform user’s activities.” Functions of Application Layer File Transfer: FTP (File Transfer Protocols): is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. Web Surfing: HTTP/HTTPS (Hyper Text Transfer Protocol/ Hyper Text Transfer Protocol): used to access the data on the World Wide Web (www). Handling E-Mails: SMTP (Simple Mail Transfer Protocol): this protocol used in sending and receiving emails over a network such as the internet. Virtual Terminals: TELNET (Teletype Network): It is a client/server application protocol that provides access to virtual terminals of remote systems. Layer 6: Presentation Layer  Presentation Layer is the 6th Layer of OSI Model  Presentation layer receives data from application layer, these data in the form of characters and numbers  Presentation layer converts these numbers and characters machine under stable binary format. Functions of Presentation Layer  Presentation layer performs 3 basic functions they are Translation, Data compression, Encryption/Decryption. Translation:  User sending data is character & number format; it converts those data in machine or binary language. Ex: Conversion of ASCII to EBCDIC Data compression:  Compression is a technique of reducing number of bits required to be represent the data.  It reduces the amount of space use to store the original file,  Size of the file reduces it can be received destination in less time.  Data compression can do faster data  Data compression is helpful in real time video, audio streaming. MIC- MCA Page 5 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 Encryption/Decryption:  To maintain the integrity of the data before transmission data is encrypted.  Security of the sensitive data at sender side data is encrypted and data is receiver side decrypted.  Encryption/decryption they are used SSl secure sockets layer protocols. Layer 5: Session Layer  It controls the connections between computers.  The session layer is networking dialog controller i.e it establishing the interaction between communication systems.  Session layers helps to setup and managing connections and enabling, sending and receiving of data followed by termination of connection sessions.  Sessions layers are some helpers they are APIs (Application Program Interface) and NETBIOS (Network Basic Input/output system). Functions of Session Layer  Session layer helps session management, authentication and authorization. Session management:  Session management is the process of maintain and controlling user sessions in a web application or system. Authentication:  Authentication is the process of verifying who you are for this user uses User Name and Password.  Once entered user name and password matched a session or connection established Authorization:  Authorization process uses by user to determine if you have permission to access a file, if not you will get a message you not authorized to access this page. Dialog control:  Communication between two processes take place in either half duplex or full duplex mode the session layer manages dialog control for this communication. Synchronization:  Session layers add synchronization points into stream of data. Layer 4: Transport Layer  The Transport layer is responsible for delivery of message from one process to another.  The network does the host to destination delivery of individual packets considering it as independent packet.  But transport layer ensures that the whole message arrives intact and in order with error control and process control.  Transport layer controls the reliability of communication Segmentation, Flow control and Error control. Functions of Transport Layer Port address:  Computer performs several operations simultaneously  Process to process delivery means specific process of one computer must be delivered to specific process on other computer.  The transport layer header therefore include port address  Network layer delivers packet to the desired computer and transport , gets messge to the correct process on that computer. MIC- MCA Page 6 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 Port no Ex: HTTP:80,HTTPS:443,SMTP:25,FTP:20 Segmentation:  Data divided into small data units called Segmentation.  Each segment contains a source number and port number helps to direct each number to the correct application and Sequence number helps to re assemble in the segments number to the correct order to form current message at the receiver. Flow control:  Transport layer performs connectionless or connection oriented services with the destination machine. Flow control:  Transport layer controls the amount of data being transferred between server & other connected devices. Error control:  If some data doesn’t arise the destination transport layer uses automatic repeat request keeps to retransmit the corrupted data  A group of bits called check sum is added to each segments by the transport layer to find out receive corrupted segments. Layer 3: Network Layer  IT play key role in data transmission  The main job of this layer is to maintain the quality of the data and pass and transmit it from source to destination  Network layer works for the transmission of received data segments from one computer to another located in different networks. Functions of Transport Layer Network layer helps to logical addressing, routing and path determination Logical addressing:  A logical address is a unique address assigned to each networks device to identify its location and enable routing. Routing:  Routing is the method of moving data packets from source to destination.  It is base on logical address of IPV4 & IPV6 Path determination:  A computer can be connect to internet server in a computer in no. of ways choosing best possible path for delivery source to destination called path determination.  OSPF (Open Shortest Path First), BGP (Border Gateway Path) uses to choose shortest path delivery. Layer 2: Data Link Layer  The data link layer is responsible for transmitting frames from one node to the next.  It transforms the physical layer to a reliable link making it an error free link to upper layer.  It helps to transfer data from one computer to another using a local medium such as a copper wire, cables, radio signals, satellites etc. Functions of Transport Layer Framing:  The frames received from network layer are divided into manageable data units called frames. Physical addressing: MIC- MCA Page 7 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  When frames are to be sent to different LAN’s, the data link layer adds a header to be frame to define sender or receiver. Flow control:  When the rate of data transmitted and rate of data reception by receiver is not same, some data may be lost  The data link layer imposes a flow control mechanism to prevent overwhelming the receiver. Error control:  Data link layer incorporates reliability to the physical layer by adding mechanism to detect and retransmit damaged or lost frames. Access control:  When multiple devices are connected to same link, the data link, the data link layer determines which device has control over link. Layer 1: Physical Layer  Physical layer is the lowest layer of the OSI model.  It co-ordinates the functions required to transmit a bit stream over a communication channel.  It deals with electrical and mechanical specifications of interface and transmission media.  It also deals with proceedings and functions required for transmission.  The data is nothing but a sequence of binary zeros and ones.  Physical layer receives bits and it converted to signals these electrical signals can be transfer through wired or wireless mode.  It can be electrical signal in case of copper cable or LAN cable.  It can be light signals in case of optical fiber  It can be radio signals in case of air.  We can say that the physical layer is responsible for carrying individual bits in a frame across the link. Functions of Physical Layer Physical characteristics of interface and media  The design issues of physical layer consider the characteristics of interface between devices and transmission media. Representation of bits:  Physical layer encodes the bits stream into electrical or optical signals. Data Rate:  The physical layer defines the duration of bits which is called as data rate of transmission rate. Synchronization of bits:  The transmission rate and receiving rate must be same; this is done by synchronization clocks at sender and receiver. The TCP/IP Reference Model  TCP/IP means Transmission Control Protocol and Internet Protocol, which are the core protocol of the internet.  It is the network model used in the current internet architecture as well.  The TCP/IP model is a fundamental frame work for computer networks.  This model defines how data is transmitted over networks, ensuring realible communication between devices.  It consist of 4 layers each layer has specific functions that help manage different aspects of network communication, making it an essential for understanding and working with modern networks. MIC- MCA Page 8 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  TCP/IP was designed and developed by the Department of defense (DOD).  The TCP/IP model is a concise version of the OSI model. OSI Model TCP/IP Model APPLICATION LAYER APPLICATION LAYER PRESENTATION LAYER SESSION LAYER TRANSPORT LAYER TRANSPORT LAYER NETWORK LAYER INTERNET LAYER DATA LINK LAYER HOST TO NETWORK LAYER PHYSICAL LAYER Protocols and networks in the TCP/IP model:  TCP/IP stands for Transmission Control Protocol / Internet Protocol.  It is a protocol suite used by most communications software.  TCP/IP is a robust and proven technology that was first tested in the early 1980s on ARPA Net, the U.S. military’s Advanced Research Projects Agency network, and the world’s first packet-switched network.  TCP/IP was designed as an open protocol that would enable all types of computers to transmit data to each other via a common communications language.  TCP/IP is a layered protocol similar to the ones used in all the other major networking architectures, including IBM’s SNA, Windows' NetBIOS, Apple’s AppleTalk, Novell’s NetWare and Digital's DECnet.  The different layers of the TCP/IP reference model are shown in Figure.  Layering means that after an application initiates the communications, the message (data) to be transmitted is passed through a number of stages or layers until it actually moves out MIC- MCA Page 9 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 onto the wire.  The data are packaged with a different header at each layer.  At the receiving end, the corresponding programs at each protocol layer unpack the data, moving it “back up the stack” to the receiving application.  TCP/IP is composed of two major parts: TCP (Transmission Control Protocol) at the transport layer and IP (Internet Protocol) at the network layer.  TCP is a connection-oriented protocol that passes its data to IP, which is a connectionless one.  TCP sets up a connection at both ends and guarantees reliable delivery of the full message sent.  TCP tests for errors and requests retransmission if necessary, because IP does not an alternative protocol to TCP within the TCP/IP suite is UDP (User Datagram Protocol), which does not guarantee delivery.  Like IP, it is also connectionless, but very useful for real-time voice and video, where it doesn’t matter if a few packets get lost. Layers of TCP/IP Reference Model 4 layers that form the TCP/IP reference model: Layer 1: Host-to-network Layer  It is a group of applications requiring network communications.  This layer is responsible for generating the data requesting connections.  It acts on behalf of the sender and the host to network layer on the behalf of the receiver.  Lowest layer of the all.  Protocol is used to connect to the host, so that the packets can be sent over it.  Varies from host to host and network to network. Layer 2: Internet layer  Selection of a packet switching network which is based on a connectionless internetwork layer is called an internet layer.  It is the layer which holds the whole architecture together.  It helps the packet to travel independently to the destination. 1. Order in which packets are received is different from the way they are sent.  IP (Internet Protocol) is used in this layer.  The various functions performed by the Internet Layer are:  Delivering IP packets  Performing routing  Avoiding congestion Layer 3: Transport Layer  It decides if data transmission should be on parallel path or single path.  Functions such as multiplexing, segmenting or splitting on the data is done by transport layer.  The applications can read and write to the transport layer.  Transport layer adds header information to the data.  Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.  Transport layer also arrange the packets to be sent, in sequence. Layer 4: Application Layer  The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc. TELNET:  It is a two-way communication protocol which allows connecting to a remote machine and run applications on it. MIC- MCA Page 10 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 FTP (File Transfer Protocol):  It is a protocol that allows File transfer amongst computer users connected over a network. It is reliable, simple and efficient. SMTP (Simple Mail Transport Protocol):  It is s a protocol, which is used to transport electronic mail between a source and destination, directed via a route. DNS (Domain Name Server):  Resolves an IP address into a textual address for Hosts connected over a network. 1. It allows peer entities to carry conversation. 2. It defines two end-to-end protocols: TCP and UDP TCP (Transmission Control Protocol):  It is a reliable connection-oriented protocol which handles byte-stream from source to destination without error and flow control. UDP (User-Datagram Protocol):  It is an unreliable connection-less protocol that does not wants TCPs, sequencing and flow control. Eg: One-shot request-reply kind of service. Merits of TCP/IP model 1. It operated independently. 2. It is scalable. 3. Client/server architecture. 4. Supports a number of routing protocols. 5. Can be used to establish a connection between two computers. Demerits of TCP/IP 1. In this, the transport layer does not guarantee delivery of packets. 2. The model cannot be used in any other application. 3. Replacing protocol is not easy. 4. It has not clearly separated its services, interfaces and protocols. EXAMPLE NETWORKS  Now days, as computers are extensively used in almost every field, we have many different types of networks.  Some of them are public networks, research networks, and co-operative networks, commercial or corporate networks.  We can distinguish between different networks on the basis of their history, administration, facilities offered, technical design and the people who use them (user communities).  Here we shall discuss some of the popular networks, such as, Novell NetWare, ARPANET, Internet, ATM network etc. ARPANET  ARPANET stands for Advanced Research Projects Agency (ARPA) Network. The network was developed in 1969 by ARPA and funded by the Department of Defence (DoD). In the mid-1960s at the height of the cold war, the DoD wanted a command and control network, which could survive the nuclear war. The traditional circuit switched telephone networks were considered too vulnerable, since the loss of one line would certainly terminate all conversations using them and might even partition the network.  The network (ARPANET) was chiefly experimental, and was used to research, develop and test networking technologies. The original network connected four host computers at four separate universities throughout the United States, enabling users to share resources and information. By 1972, there were 37 host computers connected to ARPANET. Also in that year, ARPA’s name was changed to DARPA (Defence Advanced MIC- MCA Page 11 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 Research Projects Agency). In 1973, ARPANET went beyond the boundaries of the United States by making its first international connection to England and Norway. One goal of ARPANET was to devise a network that would still be operational, even if, part of the network failed. The research in this area resulted in a set of networking rules or protocols, called TCP/IP (Transmission Control Protocol/Internet Protocol).  TCP/IP is a set of protocols that govern how data is transmitted across networks. It also enables different types of computer operating systems such as DOS and UNIX to share data across a network.  ARPANET functioned as a “backbone” network allowing smaller local networks to connect to the backbone.  Once these smaller networks were connected to the backbone, they were in effect connected to each other.  In 1983, DARPA decided that TCP/IP would be the standard set of protocols used by computers connecting to ARPANET. This meant that any smaller networks (for example, a university network) that wanted to connect to ARPANET also had to use TCP/IP. TCP/IP was available for free and was increasingly used by networks. The spread of TCP/IP helped create the Internet, as we know it today, which is the network of networks that either use the TCP/IP protocols, or can interact with TCP/IP networks.  ARPANET continued to grow, encompassing many networks from universities and government institutions. To help manage this rapidly growing “network of networks”, ARPANET was split into two networks in 1983:  ARPANET continued to be a research and development network.  MILNET an unclassified network reserved only for military sites. MILNET continues to serve this function.  In 1986, a faster backbone network called the NSFNET (National Science Foundation Network) was created. By 1989, there were over 10,000 host computers connected to the Internet.  Because of the success of the NSFNET, plans were made to phase out ARPANET. Many of the sites connected to ARPANET were absorbed by the NSFNET, and in 1990 ARPANET was officially dissolved. INTERNET  When ARPANET and NSFNET were interconnected the number of networks, machines and users grew exponentially, many regional networks joined up and connections were made across many countries.  The internet is said to have been “officially” born around 1982 when the different networks (BITNET, EARN, etc.) agreed on using the TCP/IP protocol as a standard for their interconnections making it a network of networks and overcoming some of the previous cacophony of standards, protocols and increasing its coverage.  The word Internet was coined from the words “interconnection” and “network”. Now Internet is the world’s largest computer network. It is considered to be the network of networks, and is scattered all over the world. The computers connected to the Internet may communicate with each other using fiber optic cables, telephone lines, satellite links and other media.  The development of Internet is coordinated by a non-profit organisation called the Internet Society (ISOC). Its aim is to spread the use of Internet, keep statistics of its use, helpless developed countries in building their infrastructure and Internet-technology. The Internet Architecture Board (IAB), plans long term trends and keeps a record of the RFC (Request for Comments) documents on various technical solutions and protocols used in Internet. The development is also steered by the IETF (Internet Engineering Task Force), which has several sub-groups for handling various problems and planning new standards etc. The rapid growth of Internet may also be due to several important factors: 1. Easy-to-use software - graphical browsers 2. Improved telecommunications connections 3. Rapid spread of automatic data processing, including electronic mail, bank ransfers, etc. MIC- MCA Page 12 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 4. The Information Superhighway projects. The Internet Society maintains a list of Internet service providers providing connections all over the world. There is one “universal” aspect of all computers connect to the Internet i.e., they all run the TCP/IP family of protocols. The Internet Protocol (IP) gives the physical 32-bit address, which uniquely identifies an individual computer connected to the Internet, while Transmission Control Protocol (TCP) is a connection-oriented protocol, which takes care of the delivery and order of the packages. TCP also provides the port numbers for individual services within a computer. The major information services provided by the Internet are (with the protocol in parentheses): electronic mail (SMTP), remote file copying (FTP), remote login, terminal connections (TELNET), menu-based file access (GOPHER), wide area information servers (WAIS, Z39.50), the World Wide Web (HTTP), and the Packet Internet Groper (PING). There are three major ways to connect your computer to the Internet: dial up modem access to a computer connected to Internet, dial-up networking, and leased lines (usually from a local telephone company). Switched Dial-Up Lines The most common circuit provided by public communication carriers are dial-up telephone circuits. Subscribers send routing information i.e., the dialed number to the network, which connects them to the receiver, then follow this with the information (speech). Switched circuits are not permanent. They exist only for the duration of the connection and are switched by the public network (it connects the circuits). Switched dial-up lines are not generally suited to data transmission, but are used heavily for some types of services (e.g., Bulletin Boards). Using a modem, a user can use their phone line to dial up a network provider via the phone line and connect to the Internet. At present speeds upto 56Kbps are possible over standard dial up telephone circuits. Leased Lines A leased line is a permanent non-switched end-to-end connection. Data is sent from one end to the other. It is not required to send routing information along with the data. Leased lines provide an instant guaranteed method of delivery. They are suited to high volume, high speed data requirements. The cost of the line (which is leased per month), is offset against that of toll or other rental charges. In addition, the leased line offers a significantly higher data transmission rate than the datel circuit. Very high speeds can be achieved on leased lines. The cost varies, and goes up according to the capacity (speed in bits per second) that the customer requires. WORKING OF THE WEB FIGURE: WORKING OF INTERNET The Web physically consists of your personal computer, web browser software, a connection to an Internet service provider, computers called servers that host digital data and routers and switches to direct the flow of information. The Web is known as a client-server system. Here, the Users computer is the client, and the remote computer that stores electronic files is the server. The working of the Web can be explained by the following example: MIC- MCA Page 13 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 Let’s say you want to pay a visit to the IGNOU’s website. First, you enter the address or URL of the website in your web browser (more about this in a while). Then your browser requests the web page from the web server. The IGNOU’s server sends the data over the Internet to your computer. Your web browser interprets the data and displays it on your computer screen. The glue that holds the Web together is called hypertext and hyperlinks. This feature allows electronic files on the Web to be linked so that you can easily jump between them. On the Web you can navigate through pages of information based on what interests you at that particular moment. This is commonly known as browsing or surfing the Net. To access the Web you need software such as Netscape Navigator or Microsoft Internet Explorer. These are known as web browsers. Web pages are written in a computer language called HTML, which stands for Hypertext Markup Language. NETWORK TOPOLOGY Topology refers to the shape of a network, or the network’s layout. How different nodes in a network are connected to each other and how they communicate with each other is determined by the network's topology. Topologies are either physical or logical. Some of the most common network topologies are: 1. Bus topology 2. Star topology 3. Ring topology 4. Tree topology 5. Mesh topology 6. Cellular topology. The parameters that are to be considered while selecting a physical topology are: Ease of installation. Ease of reconfiguration. Ease of troubleshooting. 1. Bus Topology  In Bus topology, all devices are connected to a central cable, called the bus or backbone. The bus topology connects workstations using a single cable. Each workstation is connected to the next workstation in a point-to-point fashion. All workstations connect to the same cable. Figure 2 shows computers connected using Bus Topology.  In this type of topology, if one workstation goes faulty all workstations may be affected as all workstations share the same cable for the sending and receiving of information. The cabling cost of bus systems is the least of all the different topologies. Each end of the cable is terminated using a special terminator.  The common implementation of this topology is Ethernet. Here, message transmitted by one workstation is heard by all the other workstations. MIC- MCA Page 14 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 Advantages of Bus Topology Installation is easy and cheap when compared to other topologies. Connections are simple and this topology is easy to use. Less cabling is required. Disadvantages of Bus Topology Used only in comparatively small networks. As all computers share the same bus, the performance of the network deteriorates when we increase the number of computers beyond a certain limit. Fault identification is difficult. A single fault in the cable stops all transmission. 2. Star Topology Figure: Star topology  Star topology uses a central hub through which, all components are connected. In a Star topology, the central hub is the host computer, and at the end of each connection is a terminal as shown in Figure 3.  Nodes communicate across the network by passing data through the hub. A star network uses a significant amount of cable as each terminal is wired back to the central hub, even if two terminals are side by side but several hundred meters away from the host. The central hub makes all routing decisions, and all other workstations can be simple.  An advantage of the star topology is that failure, in one of the terminals does not affect any other terminal; however, failure of the central hub affects all terminals.  This type of topology is frequently used to connect terminals to a large time-sharing host computer. Advantages of Star Topology Installation and configuration of network is easy. Less expensive when compared to mesh topology. Faults in the network can be easily traced. Expansion and modification of star network is easy. Single computer failure does not affect the network. Supports multiple cable types like shielded twisted pair cable, unshielded twisted pair cable, ordinary telephone cable etc. Disadvantages of Star Topology Failure in the central hub brings the entire network to a halt. More cabling is required in comparison to tree or bus topology because each node is connected to the central hub. MIC- MCA Page 15 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 3. Ring Topology Figure: Ring topology  In Ring Topology all devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it, i.e., the ring topology connects workstations in a closed loop, which is depicted in Figure Each terminal is connected to two other terminals (the next and the previous), with the last terminal being connected to the first. Data is transmitted around the ring in one direction only; each station passing on the data to the next station till it reaches its destination.  Information travels around the ring from one workstation to the next. Each packet of data sent on the ring is prefixed by the address of the station to which it is being sent. When a packet of data arrives, the workstation checks to see if the packet address is the same as its own, if it is, it grabs the data in the packet. If the packet does not belong to it, it sends the packet to the next workstation in the ring.  Faulty workstations can be isolated from the ring. When the workstation is powered on, it connects itself to the ring. When power is off, it disconnects itself from the ring and allows the information to bypass the workstation.  The common implementation of this topology is token ring. A break in the ring causes the entire network to fail. Individual workstations can be isolated from the ring. Advantages of Ring Topology Easy to install and modify the network. Fault isolation is simplified. Unlike Bus topology, there is no signal loss in Ring topology because the tokens are data packets that are re-generated at each node. Disadvantages of Ring Topology Adding or removing computers disrupts the entire network. A break in the ring can stop the transmission in the entire network. Finding fault is difficult. Expensive when compared to other topologies. 4. Tree Topology Figure: Tree topology  Tree topology is a LAN topology in which only one route exists between any two nodes on the network. The pattern of connection resembles a tree in which all branches spring from one root. Figure 5 shows computers connected using Tree Topology. MIC- MCA Page 16 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  Tree topology is a hybrid topology, it is similar to the star topology but the nodes are connected to the secondary hub, which in turn is connected to the central hub. In this topology groups of star-configured networks are connected to a linear bus backbone. Advantages of Tree Topology Installation and configuration of network is easy. Less expensive when compared to mesh topology. Faults in the network can be detected traced. The addition of the secondary hub allows more devices to be attached to the central hub. Supports multiple cable types like shielded twisted pair cable, unshielded twisted pair cable, ordinary telephone cable etc. Disadvantages of Tree Topology Failure in the central hub brings the entire network to a halt. More cabling is required when compared to bus topology because each node is connected to the central hub. 5. Mesh Topology Figure: Mesh Topology  Devices are connected with many redundant interconnections between network nodes. In a well-connected topology, every node has a connection to every other node in the network. The cable requirements are high, but there are redundant paths built in. Failure in one of the computers does not cause the network to break down, as they have alternative paths to other computers.  Mesh topologies are used in critical connection of host computers (typically telephone exchanges). Alternate paths allow each computer to balance the load to other computer systems in the network by using more than one of the connection paths available. A fully connected mesh network therefore has n (n-1)/2 physical channels to link n devices. To accommodate these, every device on the network must have (n-1) input/output ports. Advantages of Mesh Topology Use of dedicated links eliminates traffic problems. Failure in one of the computers does not affect the entire network. Point-to-point link makes fault isolation easy. It is robust. Privacy between computers is maintained as messages travel along dedicated path. Disadvantages of Mesh Topology The amount of cabling required is high. A large number of I/O (input/output) ports are required. MIC- MCA Page 17 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025 6. Cellular Topology Figure: Cellular topology  Cellular topology, divides the area being serviced into cells. In wireless media each point transmits in a certain geographical area called a cell, each cell represents a portion of the total network area. Figure 7 shows computers using Cellular Topology.  Devices that are present within the cell, communicate through a central hub. Hubs in different cells are interconnected and hubs are responsible for routing data across the network. They provide a complete network infrastructure.  Cellular topology is applicable only in case of wireless media that does not require cable connection. Advantages of Cellular Topology If the hubs maintain a point-to-point link with devices, trouble shooting is easy. Hub-to-hub fault tracking is more complicated, but allows simple fault isolation. Disadvantages of Cellular Topology When a hub fails, all devices serviced by the hub lose service (are affected). TYPES OF COMPUTER NETWORKS Based on the size of the network, ownership, and distance covered by the network, there are three types of computer networks 1. Local Area Network (LAN) 2. Metropolitan Area Network (MAN) 3. Wide area network (WAN) Refer to the below image to show the types of computer networks  Computer Network is the interconnection of multiple devices.  Mainly there are three types of computer networks: LAN (Local Area Network), WAN (Wide Area Network), and MAN (Metropolitan Area Network).  LAN is used to connect devices in a small area like a building, office, etc. MIC- MCA Page 18 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  MAN covers the devices connected within a town or a city.  WAN covers a large geographical area such as a continent or a country.  System Area Network, Home Area Network, and Campus Area Network are some other network types LAN (LOCAL AREA NETWORK) 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. It is a network mostly used for sharing hardware resources such as printers, files, scanners, etc. If we talk about the simplest LAN network then we will consider a computer and a printer connected in a home as the simplest network. The data transmission speed of the LAN is up to 10 Mbps. There are two types of LAN: Wired LAN– In this type of LAN, wired cables such as twisted pair or coaxial cables are used for the connection and transmission of data. Wireless LAN– In this type of LAN, devices are connected by wireless cables such as radio, and light waves. Characteristics  LAN is a type of network owned by the private owner  LAN can be used to connect printers, personal computers, etc.  LAN Networks can be designed very easily.  Troubleshooting of LAN networks is easy.  Data transfer rate of the LAN network is about 10 Gbits/s. MIC- MCA Page 19 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  It is a network which is limited to the local area.  LAN operates relatively faster than the WAN network. Advantages  LAN allows sharing of computer hardware like printers, scanners, etc. which may reduce the cost of buying expensive computer hardware.  LAN permits to share of a single internet facility among the devices connected to LAN.  LAN provides high security and fault tolerance capability.  It allows the transmission of data between people and devices at a high transmission rate. Disadvantages  LAN reduces the cost by allowing sharing of computer hardware, but the initial installation cost of LAN is very high.  Technical and skilled manpower is required for the configuration and installation of the LAN network.  Due to the sharing of computer resources among the devices, sometimes the operation speed of the network may slow down. MAN (METROPOLITAN AREA NETWORK)  A Metropolitan Area Network or MAN is a network connecting devices across an entire town, entire city, or any other small region.  This is a network larger than LAN but smaller than the WAN.  MAN network works between LAN and WAN.  MAN can be used to connect multiple LAN networks.  When one LAN uses modems, direct digit devices, and any other media types to connect with other LAN, then it covers a large area which is considered a Metropolitan Area Network (MAN). Characteristics  MAN is a larger network in comparison to LAN.  MAN network generally covers the towns and cities in a maximum of 50 km range  MAN is the most used medium in cables and optical fibers. Advantages  MAN network connects all the branches of the company that exist in the same city.  Dual Bus in MAN networks permits bidirectional data transfer concurrently. MIC- MCA Page 20 COMPUTER NETWORKS (24MC2T01) I M.C.A/II SEM YEAR: 2024-2025  MAN network is considered economical as it allows the sharing of resources among all the branches of the company which are in the city. Disadvantages of Metropolitan Area Networks  MAN requires high initial costs to set up because fiber-optic cables and other networking equipment can be expensive.  MAN requires highly technical people to set up.  It requires regular maintenance to provide the best performance.  As compared to LAN, MAN is more complex to implement.  As the geographical area in MAN increases, it is at risk of being attacked by hackers; hence, more security measures are followed to protect against intruders.  It is hard to make the system safe from hackers.  It becomes very difficult to manage if the size and number of LANs increase.  Its reach is limited to a 50-kilometer area, so organizations located beyond the metropolitan area require a WAN connection. WAN (WIDE AREA NETWORK)  A WAN stand for Wide Area Network is a type of computer network which can cover a large geographical area such as a continent, or a country.  The size of the WAN network is larger than the LAN and MAN network.  When the size of the network grows more than the MAN then it is considered a WAN.  Usually, telecommunication networks are considered a Wide Area Network.  WAN Network could be an interconnection between two or more LANs that are connected through telephone lines or radio waves. Characteristics  WAN is used to cover a large geographical area, like a country.  WAN can be used to connect within the world and around the world.  Any office and organization can use WAN to form its global integrated network. Advantages  WAN allows covering a large geographical area.  Offices situated at longer distances from each other can easily communicate through WAN.  Allows connecting devices like mobile phones, laptops, tablets, etc. Disadvantages  There are more chances of error and issues because of the use of more technologies and wide coverage.  Provides less security in comparison to other types of networks.  The initial and configuration cost of WAN is very high.  Skilled technicians and network administrators are required for the setup of this network. MIC- MCA Page 21