Ch-2 Data Communication PDF

Topics: 1. Introduction to Networks 2. Use of computer network 3. Network hardware 4. Network software 5. OSI Model(Open system interconnect) 6. TCP/IP Model 7. Comparison 8. The internet Data Communication  Communication is the process of exchanging information.  Telecommunicat...

Topics: 1. Introduction to Networks 2. Use of computer network 3. Network hardware 4. Network software 5. OSI Model(Open system interconnect) 6. TCP/IP Model 7. Comparison 8. The internet Data Communication  Communication is the process of exchanging information.  Telecommunication means communication at distance e.g. telephony, telegraphy, television etc.  Data: Information presented in any form agreed upon by the parties creating and using data.  Data Communication: the exchange of data between two devices via some form of transmission medium.  Effectiveness of data communication depends on: 1. Delivery: Must deliver to correct destination 2. Accuracy: Data deliver correctly, unaltered or error free. 3. Timeliness: Timely manner and real time transmission. 4. Jitter: Variations in packet arrival time. Data Communications and Networking: Behrouz Forouzan, 4th Edition. Data Communication System Components Figure 1 Five components of data communication Five Components of data communication includes 1. Message: Data in any form like Audio, Text, Video, Computer data, Picture etc. 2. Sender: Any Computer, Workstation, Telephone Handset, Video Camera etc. 3. Receiver 4. Transmission Medium: Any Wired or Wireless Medium. 5. Protocol: Set of rules that governs the data communication or agreement between communicating devices. Data Communications and Networking: Behrouz Forouzan, 4th Edition. Network  A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Data Communications and Networking: Behrouz Forouzan, 4th Edition. Uses of Computer Network  Business Applications:  Monitor Production, keep inventory, do the payroll.  Resource Sharing  Proximities between headquarter and Area Offices Computer Networks: Andrew Tanenbaum, 4th Edition.  Uses of Computer Network  Business Applications:  Client Server Model: Client : Simple user computer in network Server : Powerful Computer on which data  Small Network with is stored  Two clients  One server Computer Networks: Andrew Tanenbaum, 4th Edition.  Uses of Computer Network  Business Applications:  Client Server Model: Request : Message send by client to server  Request Reply : Reply by server to client based on request  Response Computer Networks: Andrew Tanenbaum, 4th Edition. Uses of Computer Network  Business Applications:  Email:  Video Conferencing  Webinars  E-commerce Computer Networks: Andrew Tanenbaum, 4th Edition. Uses of Computer Network  Home Applications:  Access the remote information (WWW)  E-paper and Online Libraries  Instant Messaging  Chat Rooms Computer Networks: Andrew Tanenbaum, 4th Edition. Uses of Computer Network  Home Applications:  Peer to Peer Communication (Napster)  Online Music, Sharing Playlists  Photo Sharing  E-learning  Online Games  Video On Demand https://en.wikipedia.org/wiki/Napster Uses of Computer Network  Mobile Applications:  PDA, Notebooks & Mobile Wireless  Wireless Networks WLAN, WiFi  Bill Payment  Courier Tracking  M-commerce https://en.wikipedia.org/wiki/Napster  Network devices  Router: A router is a network device that connects different networks together and determines the best path for data packets to travel between them. It acts as an intermediary device and is responsible for directing data traffic between devices on the local network (LAN) or between the local network and the internet (WAN). Routers use IP addresses to make forwarding decisions, and they provide functionalities like Network Address Translation (NAT) to allow multiple devices to share a single public IP address. LOGO  Network devices  Switch: A switch is a network device used to create a local network (LAN) by connecting multiple devices, such as computers, printers, and servers. It operates at the data link layer (Layer 2) of the OSI model and uses MAC addresses to forward data packets to the appropriate destination device within the same network. Unlike hubs, switches are more intelligent and efficient, as they can handle simultaneous data transmissions to different devices without causing collisions. LOGO  Network devices  Hub: A hub is an older and simpler networking device that operates at the physical layer (Layer 1) of the OSI model. It acts as a central connection point for devices in a local network (LAN) and broadcasts all data it receives to all connected devices. As a result, collisions can occur in a hub-based network, leading to reduced efficiency and performance. For this reason, switches have mostly replaced hubs in modern networks. LOGO  Network devices  Modem: A modem (short for modulator-demodulator) is a device that converts digital signals from a computer or network into analog signals that can be transmitted over analog communication lines, such as a telephone line or cable line. On the receiving end, it converts the analog signals back into digital signals that computers or network devices can understand. Modems are commonly used to establish internet connections over telephone lines (DSL) or cable lines (cable modems). LOGO  Network devices  Gateway: A gateway is a networking device or software system that acts as an entry and exit point between two different networks, often with different protocols. It provides a translation layer to allow communication between networks that use different technologies or protocols. Gateways are commonly used in scenarios where two networks need to communicate, such as connecting a local network to the internet, where the router itself can act as a gateway. LOGO  Comparison a router connects different networks and routes data between them, a switch connects devices within a single network, a hub is an outdated and less efficient version of a switch, a modem converts digital signals to analog for transmission over communication lines, and a gateway facilitates communication between two different networks. LOGO Network Hardware: Data Flow Figure 2 Data flow (simplex, half-duplex, and full-duplex) Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Network Hardware: Physical Structure Dedicated Link Entire capacity is reserved. Shared Link Spatially or Time Shared connection. Figure 3 Types of connections: point-to-point and multipoint Link: Communication Pathway that transfers data. Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Network Hardware: Physical Topology Topology: Way in which network is laid out physically. Two or more devices connect to a link. It is geometric representation of the relationship of all links and devices. Figure 4 Categories of topology Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Physical Topology: Mesh Mesh: Every device has dedicated point to point link. Dedicated: Traffic carries only between the two devices it connects. Total Links = n (n-1) /2 Advantages: Disadvantages: 1.Link carries its own data 1.Number of I/O 2.Robust 2.Sheer bulk of wiring 3.Privacy & Security greater than space. 4.Easy Fault 3.Expensive. Identification & Isolation. Figure 5 A fully connected mesh topology (five devices) Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Physical Topology: Star Star: Every device has dedicated point to point link with central controller Hub. No direct traffic between nodes. Advantages: 1.Less expensive than Disadvantages: Mesh. 2.Easy Install & 1.Dependency of whole Reconfiguration. topology on Hub. 3.Less cabling. 4.Robust. 5.Easy Fault Identification. Figure 6 A star topology connecting four stations Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Physical Topology: Bus Point to Multipoint. Bus: Long cable acts as a backbone link to all the devices in network. Nodes connected by drop lines and taps. Tap is connector that either splices the main cable or punctures the sheathing of cable. Disadvantages: Advantages: 1.Dependency of whole 1.Less expensive than topology on Bus. Mesh. 2.Difficult 2.Easy Install & reconfiguration and Reconfiguration. fault identification. 3.Less cabling. 3.Signal reflections. 4.Robust. Figure 7 A bus topology connecting three stations Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Physical Topology: Ring Each device has dedicated point to point connection with only two devices on either side of it. Signal pass along the ring in one direction until it reach destination. Advantages: Disadvantages: 1.Easy to install and reconfigure. 1.Unidirectional 2.Addition/ deletion traffic of node is easy. 2.Maximum Ring 3.Easy faulty length and number isolation as signal of devices. circulating all the time. Figure 8 A ring topology connecting six stations Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Physical Topology: Hybrid Main topology is star with each branch connecting several stations in a bus. Figure 9 A hybrid topology connecting six stations Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Category of Networks: Local Area Network LAN: Privately owned and links devices in a single office, building or campus. Shares resources like printers, scanner, HDD, applications etc. LAN size limited to few kilometers. Data ranges from Mbps to few Gbps e.g. 1Gbps or 100 Mbps Mostly copper and short distance optic cabling (multimode) Figure 10 An isolated LAN connecting 12 computers to a hub in a closet Data Communications and Networking: Behrouz Forouzan, 4th Edition. Category of Networks: Wide Area Network WAN: Long distance complex backbone network that connect the Internet and many LANS through Routers and Gateways. WAN spans over country or continent size is between hundred to thousand Km. Data ranges to few Mbps. Mostly leased circuits Figure 11 A WAN Data Communications and Networking: Behrouz Forouzan, 4th Edition. Category of Networks: Metropolitan Area Network MAN: Sizes between LAN & WAN. Covers the city e.g. Cable TV network or telephone company network providing high speed DSL. LAN size limited to city or town within few hundred kilometers. Data ranges to Mbps. Mostly long distance optic cabling (single mode) Figure 12 A metropolitan area network based on cable TV. Computer Networks: Andrew Tanenbaum, 4th Edition. Category of Networks: internetwork of LAN & WAN Figure 13 A heterogeneous network Data Communications and Networking: Behrouz Forouzan, 4th Edition. Category of Networks: The Internet The Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link billions of devices worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies. The Internet carries an extensive services like HTTP documents, WWW, File Figure 14 Hierarchical of the Internet sharing, email, telephony and lot more. https://en.wikipedia.org/wiki/List_of_internet_service_providers_in_India Computer Network Types: Spatial Scope  Local Area Network (LAN)  Home Area Network (HAN)  Storage Area Network (SAN)  Campus/Corporate Area Network (CAN)  Backbone Network  Metropolitan Area Network (MAN)  Wide Area Network (WAN)  Cloud/Internet Area Network (IAN)  Internet  Interplanetary Internet https://en.wikipedia.org/wiki/List_of_internet_service_providers_in_India  The Internet: Protocols  Computer Network communicates between Entity.  Protocol is a set of rules that governs data communication.  Protocol defines what is communicated, how it is communicated, when it is communicated.  The key elements of protocol are:  Syntax: Structure or format of data.  Semantics: The meaning of each section of bits. i.e. how particular pattern is interpreted, what action to be taken from interpretation.  Timing: When data should be sent How fast data should be sent. Data Communications and Networking: Behrouz Forouzan, 4th Edition.  The Internet: Standards  Standards are essential in creating and maintaining an open, competitive market for equipment manufacturing and in guaranteeing national and international interoperability of data and telecommunication technology and processes.  Standards provide guidelines to manufacturer, vendors, governments agencies and other service providers to ensure the interconnectivity.  Standard Organizations are:  International Organization for Standards (ISO)  International Telecommunication Union (ITU-T)  Consultative Committee for International Telegraphy and Telephony (CCITT)  American National Standards Institute (ANSI)  Institute of Electrical and Electronics Engineers (IEEE)  Electronics Industries Association (EIA) Data Communications and Networking: Behrouz Forouzan, 4th Edition. Network Software: The Layered Tasks  Network = Hardware (Physical equipment that carries signals) + Software (instruction sets that make the service possible) Figure 15 Tasks involved in sending a letter Data Communications and Networking: Behrouz Forouzan, 4th Edition.  Network Software: The Layered Tasks  To reduce design complexity, most networks organized as a stack of layers or levels.  The number of layers, name of layers, contents of layers, functions of layers differ from network to network.  Layer n on one machine  Layer n on another. (Peer layers)  Interfaces defines which primitive operations and services lower layer offers to upper layer.  Layers & protocols knows as Network Architecture.  List of protocols used known as protocol stack. Figure 16 Layers, protocols, and interfaces. Computer Networks: Andrew Tanenbaum, 4th Edition. Design Issues for the Layers  Some of the key design issues that occur in computer networks are as below.  Addressing: Mechanism for Identifying senders and receivers.  Error Control: Error Detection and Error Correction as Physical communication circuits are never perfect.  Flow Control: How to keep fast sender from swamping a slow receiver with data.  Framing: How to handle arbitrarily long message by disassembling, transmitting, and then reassembling messages.  Multiplexing and Demultiplexing: In case of expensive set up for a separate connections, all the traffic for all connections has to be sent over at most a few physical circuits.  Routing: Decision of path selection in case of multiple path exists between source and destination. Computer Networks: Andrew Tanenbaum, 4th Edition. The Reference Models:  The layered tasks in networks are achieved through two important network architecture. 1. OSI Reference Model:  Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s.  OSI model is rarely used any more, but it is generalized and still valid at features discussed at each layer. 2. TCP/IP Model:  This model itself is not of much use but the protocols are widely used. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Models: Layered Architecture  The Open System Interconnect (OSI) reference model is a framework for the design of network systems that communicate across all types of computer systems.  It consists of seven separated but related layers, each of which defines a segment.  The process on each machine that communicate at a given layer are called peer-to-peer processes. Figure 17 The OSI Model. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Peer- Peer-to to--Peer Processes Figure 18 The interaction between layers in the OSI model Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Layered Architecture Segment Packet Frames Bit Figure 19 An exchange using the OSI model Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Physical Layer  The physical layer is responsible for movement of individual bits from one hop to the next.  It deals with mechanical and electrical specifications of the interface and transmission medium.  Defines procedures and functions that physical devices/interfaces have to perform. Figure 20 An exchange using the OSI model Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Physical Layer  Duties of Physical Layer:  Physical Characteristics of interfaces and medium: Type of transmission medium  Representation of bits: Type of encoding, voltage levels.  Data Rate: Number of bits sent per second.  Synchronization of bits: Sender-Receiver data rate, clock, bit levels.  Line Configuration: Dedicated Line/ Shared Line  Physical Topology: How devices are connected in network.  Transmission Mode: Direction of transmission between two devices i.e. Simplex, Half duplex, full duplex. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Data Link Layer  The data link layer is responsible for moving frames from one hop (node) to the next.  DLL transforms the physical layer to a reliable link by making it appear error free to the upper layers. Figure 21 Data link layer Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Data Link Layer  Duties of Data Link Layer:  Framing: divides the stream of bits into manageable data units called frames.  Physical addressing: DLL adds header to the frame to define the sender and/or receiver.  If frame is intended for receiver outside network, then address is of the device that connects the network to the next one.  Flow Control: flow control mechanism to avoid overwhelming the receiver.  Error Control: error detection and correction by adding trailer at the end of frame.  Access Control: when two or more devices on the same link, DLL protocols determine which device has control over the link. Data Communications and Networking: Behrouz Forouzan, 4th Edition. Data Link Layer: Hop to Hop Delivery Figure 22 Data link layer: Hop to Hop Delivery Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Network Layer  The network layer is responsible for the delivery of individual packets from the source host to the destination host possibly across multiple networks.  DLL oversees the delivery of packets between two systems on same network. Figure 22 Network layer Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Models: Network Layer  Duties of Network Layer:  Logical Addressing: the network layer adds a header to packet coming from the upper layer that, among the other thing, includes logical address of the sender and receiver.  Routing: when independent networks or links are connected to create internetworks or large network, the connecting devices (routers or switches) route the packets to their final destinations.  One of the major function of network layer is to provide this routing mechanism. Data Communications and Networking: Behrouz Forouzan, 4th Edition. Network Layer: Source to Destination Delivery Figure 23 Network layer: Source to destination Delivery Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Model: Transport Layer  The transport layer is responsible for the delivery of a message from one process to another process of entire message.  A process is an application running on a host.  Network layer does not recognize any relationship between those packets, it treats everyone independently, as all belongs to separate message. Figure 23 Transport layer Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Model: Transport Layer Figure 24 Reliable process-to-process delivery of a message Data Communications and Networking: Behrouz Forouzan, 4th Edition.  OSI Reference Model: Transport Layer  Duties of Transport Layer:  Service point addressing: specific process(running program) on one computer to a specific process on the other. The transport layer header includes a type of address known as service point address (port address)  Segmentation and reassembly: message divided into transmittable segment with a sequence number. So reassembling message correctly at destination to identify/replace packets lost during transmission.  Connection control: Connection Oriented or Connection less delivery of packets.  Flow control: End to End flow control rather across a single link.  Error Control: Process to Process error control. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Model: Session Layer  The session layer is responsible for dialog control and synchronization.  The session layer is the network dialog controller. It establishes, maintain, and synchronizes the interaction among communicating systems. Figure 25 Session layer Data Communications and Networking: Behrouz Forouzan, 4th Edition.  OSI Reference Model: Session Layer  Duties of Session Layer:  Dialog Control: Allows two systems to enter into a dialog. i.e. Half duplex or full duplex.  Synchronization: Session allows a process to add checkpoints or synchronization points. E.g. 2000 pages, its advisable to insert checkpoints after every 100 pages to ensure that each 100 page unit is received and acknowledge independently. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Model: Presentation Layer  The presentation layer is responsible for translation, compression, and encryption.  It is concerned with syntax and semantics of information exchanged between two systems. Figure 26 Presentation layer Data Communications and Networking: Behrouz Forouzan, 4th Edition.  OSI Reference Model: Presentation Layer  Duties of Presentation Layer:  Translation: As the different computer uses different encoding systems, presentation layer is responsible for interoperability between different encoding methods. It changes information format from sender/receiver independent common format.  Encryption: to carry sensitive information, original message is encrypted in another form before sending over network.  Decryption reverses original process to transform the message back.  Compression: reduces the number of bits contained in information important for transmission of multimedia such as text, audio and video. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Reference Model: Application Layer  The application layer enables the user or software, to access the network.  Provides user interfaces and support for services such as email, remote file access and transfer, shared database management.  The application layer is responsible for providing services to the user. Figure 27 Application layer Data Communications and Networking: Behrouz Forouzan, 4th Edition.  OSI Reference Model: Application Layer  Duties of Application Layer:  Network Virtual Terminal: software version of physical terminal, allows user to log on to a remote host.  File transfer, access and management: allows user to read, change or retrieve files from remote computer.  Mail services:  Directory services: distributed database sources and access for global information about various objects and services. Data Communications and Networking: Behrouz Forouzan, 4th Edition. OSI Model: Figure 29 Protocol Stack Data Communications and Networking: Behrouz Forouzan, 4th Edition.  TCP/IP Model:  The ability to connect multiple networks in a seamless way was one of the major design goal.  This architecture i.e. TCP/IP model was developed prior then the OSI model around 1974.  The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, Figure 28 TCP/IP Model transport, and application. Computer Networks: Andrew Tanenbaum, 4th Edition. TCP/IP Model: Figure 29 TCP/IP Model Data Communications and Networking: Behrouz Forouzan, 4th LOGO Edition.  TCP/IP Model: The Internet Layer  Requirements led to the packet switching network based on connection less internetwork layer.  IP (Internetworking protocol)  Unreliable and connection less protocol –A best effort delivery.  No error checking.  IP transforms packet in datagram format.  Data gram can travel along different route and can arrive out of sequence.  ICMP (internet control message protocol)  To send notification of datagram to sender. sends query and error reporting messages.  IGMP (Internet group management protocol)  ARP (Address resolution protocol): Associating logical address with physical address.  Used to find physical address when logical address is known  RARP (Reverse ARP) : provides IP address when physical address is known. Computer Networks: Andrew Tanenbaum, 4th Edition. LOGO  TCP/IP Model: The Transport Layer  Responsible for delivery of message from one running process to another process.  Similar to OSI Model.  End-to-End transport layer protocols.  TCP (Transmission control protocol)  UDP (User datagram protocol)  SCTP (Stream control transmission protocol)  Combines best features of TCP And UDP Computer Networks: Andrew Tanenbaum, 4th Edition. LOGO  TCP/IP Model: TCP - UDP  TCP : Reliable connection oriented protocol  Allows byte streaming originating at one m/c to be delivered without error on any other m/c in internet.  Divides a stream of data into smaller units called segment.  Segments have sequence number for reordering.  TCP collects data grams from IP and reorders them based on sequence number.  Receiver will reassemble the received message.  Also handles flow control.  UDP: User Datagram Protocol  Unreliable  Process to process protocol  Adds port address, checksum error control and length information. Computer Networks: Andrew Tanenbaum, 4th Edition. LOGO  TCP/IP Model: The Application Layer  Contains all higher level protocols.  TELNET (Provides bidirectional text oriented communication).  FTP (File transfer protocol)  SMTP (Simple mail transfer protocol)  DNS (domain name system)  HTTP Computer Networks: Andrew Tanenbaum, 4th Edition. LOGO  OSI Model Vs TCP/IP Model:  The OSI and TCI/IP models have much in common.  Functionality of layers is roughly similar.  Three concepts are central to the OSI model:  Services: layer performs some services for the layer above. The service defines what layer does.  Interfaces: it tells the processes above it how to access it and specifies what parameters are and what results to expect.  Protocols: they used in a layer are layer’s own business.  The TCP/IP model did not clearly defines service, interface while protocols are hidden in OSI model.  TCP/IP model can be replaced relatively easily as technology changes.  In the TCP/IP model protocols came first, model was just description of existing protocols.  In the OSI model, model came first, then according to the services and duties of interfaces protocols were fit later. LOGO  OSI Model Vs TCP/IP Model:  The OSI model supports both connection less and oriented communication in the network layer, but only connection oriented communication in transport layer.  While TCP/IP model has only connectionless mode in the network layer, but supports both in the transport layer, giving user a choice. LOGO Addressing: Figure 37 Addresses in TCP/IP Data Communications and Networking: Behrouz Forouzan, 4th LOGO Edition. Addressing: Figure 38 Relationship of layers and addresses in TCP/IP Data Communications and Networking: Behrouz Forouzan, 4th LOGO Edition. SMTP:Simple Mail Transfer Protocol. It is a protocol used for sending and receiving email messages over a network. FTP: stands for File Transfer Protocol. It is a standard network protocol used to transfer files from one host (usually a computer) to another over a TCP-based network, such as the internet. FTP is a client-server protocol, which means it involves two entities: the FTP client and the FTP server. LOGO HTTP stands for Hypertext Transfer Protocol. It is a protocol used for transferring data over the internet. More specifically, it is the foundation of data communication on the World Wide Web, enabling the retrieval and display of web content in web browsers. HTTP operates at the application layer of the TCP/IP protocol suite and is the basis for how web browsers interact with web servers. LOGO DNS stands for Domain Name System. It is a hierarchical decentralized naming system used to translate human-readable domain names (such as www.example.com) into IP addresses (such as 192.0.2.1) that computers use to identify each other on a network. DNS plays a vital role in the functioning of the internet by providing a way to access websites and other resources using easily recognizable domain names instead of numeric IP addresses. LOGO SNMP stands for Simple Network Management Protocol. It is an internet-standard protocol used to manage and monitor network devices, servers, and other network-connected equipment. SNMP allows network administrators to collect information, monitor performance, and manage configurations of network devices in a standardized and consistent manner. It is widely used for network monitoring, troubleshooting, and remote management. LOGO TELNET is a network protocol that allows users to establish a command-line session on a remote host over a network, typically the internet or a local area network (LAN). It enables terminal emulation, allowing a user to remotely access and control another computer as if they were physically present at the remote machine's console. TELNET is often used for remote administration, configuration, and troubleshooting of networked devices. LOGO SCTP stands for Stream Control Transmission Protocol. It is a transport layer protocol that provides several advantages over traditional transport protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). SCTP is designed to support reliable and message-oriented communication between two endpoints in a network. It was initially developed to address certain limitations of TCP and UDP in various scenarios. LOGO TCP stands for Transmission Control Protocol. It is one of the core protocols of the TCP/IP suite, which forms the basis for communication on the internet and many other computer networks. TCP provides reliable, connection-oriented communication between devices over a network. It ensures that data is delivered accurately and in the correct order, making it suitable for applications where data integrity and consistency are crucial. LOGO UDP stands for User Datagram Protocol. It is a transport layer protocol that provides a connectionless and lightweight means of communication between devices over a network. UDP is often contrasted with TCP (Transmission Control Protocol), which offers a reliable and connection-oriented communication channel. UDP is used for applications where speed and reduced overhead are prioritized over guaranteed delivery and error checking. LOGO ICMP stands for Internet Control Message Protocol. It is an essential protocol within the TCP/IP suite that is primarily used for diagnostic and error-reporting purposes in IP networks. ICMP provides a way for network devices to exchange control messages and information about network conditions, connectivity, and errors. LOGO IGMP stands for Internet Group Management Protocol. It is a network-layer protocol used to manage and control multicast group membership within IP networks. Multicast refers to the transmission of data from one sender to multiple receivers who are interested in receiving the data. IGMP is an essential component of IP multicast communication and is used to ensure that multicast traffic is delivered only to the devices that are part of a specific multicast group. LOGO RARP stands for Reverse Address Resolution Protocol. It is an obsolete networking protocol used to map MAC addresses (hardware addresses) to IP addresses in a local area network (LAN). RARP serves as a counterpart to ARP (Address Resolution Protocol), which maps IP addresses to MAC addresses. LOGO ARP stands for Address Resolution Protocol. It is a fundamental networking protocol used to map an IP address to a physical hardware address, such as a MAC (Media Access Control) address. ARP plays a crucial role in facilitating communication between devices on a local network, especially in Ethernet-based networks. LOGO Repository  http://highered.mheducation.com/sites/007296 7757/information_center_view0/index.html  http://authors.phptr.com/tanenbaumcn4/  http://nptel.ac.in/courses/106105081  http://www.soundtraining.net/