Introduction to Computer Network PDF

Introduction to COMPUTER NETWORK COMPUTER NETWORK Is defined as the interconnection of two or more computers. It is done to enable the computers to communicate and share available resources. COMPUTER NETWORK Is a group of devices connected with each other through a...

Introduction to COMPUTER NETWORK COMPUTER NETWORK Is defined as the interconnection of two or more computers. It is done to enable the computers to communicate and share available resources. COMPUTER NETWORK Is a group of devices connected with each other through a transmission medium such as wires, cables etc. These devices can be computers, printers, scanners, Fax machines etc. COMPUTER NETWORK The purpose of having computer network is to send and receive data stores in other devices over the network. These devices are often referred as nodes. Nodes – is a connection point that can receive, create, store or send data along distributed network routes. Five basic components of a computer network: Five basic components of a computer network: Message – it is the data or information which needs to be transferred from one device to another device over a computer network. Sender – is the device that has the data and needs to send the data to other device connected to the network. Five basic components of a computer network: Receiver – is the device which is expecting the data from other device on the network. Transmission media- use to transfer data from one device to another device through wires, cables, radio waves etc. Five basic components of a computer network: Protocol – is a set of rules that are agreed by both sender and receiver, without a protocol two devices can be connected to each other but they cannot communicate. Networks are used to:  Sharing of resources such as printers  Sharing of expensive software’s and database  Communication from one computer to another computer  Exchange of data and information among users via network  Sharing of information over geographically wide area Components of Computer Network:  Two or more computers  Cables as linked between the computers  A network interfacing card (NIC) on each other. The main purpose of NIC is to format the data, send the data and receive the data at the receiving node.  Switches  Software called Operating System (OS) Network Benefits:  The network benefits can be divided into two categories:  Sharing  Connectivity Sharing Resources  Types of resources are: 1. Hardware: A network allows users to share many hardware devices such as printers, modems, fax machine, CD ROM, players, etc. 2. Software: sharing software resources reduces the cost of software installation, Other Benefits of Computer Network  Increased speed  Reduces cost  Improves security  Centralized software managements  Electronic mail  Flexible access Disadvantages of Computer Networks  High cost of installation  Requires times for administration  Failure of server  Cable faults Assignment: Print in Short Bond Paper 1. What are the 5 most common type of computer networking? 2. Illustrate the 5 most common type of computer network and their functions. NO. TYPE OF COMPUTER ILLUSTRATION FUNCTION NETWORK 1 2 3 4 5 Assignment: Print in Short Bond Paper 1. Give 2 advantages of a computer network. 2. Give 2 disadvantages of a computer network. 3. What type of computer network do you think our school has installed? 4. What is peer-to-peer network? Illustrate sample. Types of Computer Networks Different Types of Networks Depending upon the geographical are covered by a network, it is classifies as: - Local Area Network (LAN) - Metropolitan Area Network (MAN) - Wide Area Network (WAN) - Personal Area Network (PAN) Local Area Network (LAN) is a network that is used for communicating among computer devices, usually within an office building or home. it’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users. Has lower cost compared to MAN’s or WAN’s Local Area Network (LAN)  Advantages of LAN Disadvantages of LAN Speed Expensive to install Cost Requires Security administrative time E-mail File Server May Resource Sharing Fail Cable may Break  Metropolitan Area Network (MAN) is a large computer network that usually spans a city or a large campus. It is optimized for a large geographical area than a LAN, ranging from several blocks of buildings to entire cities. It often acts as a high speed network to allow sharing of regional resources.  Metropolitan Area Network (MAN) Examples of MAN: Telephone company that provides a high speed DSL to customers and cable TV network. Metropolitan Area Network (MAN)  Wide Area Network (WAN) Multiple LANs can be connected together using devices such as bridges, routers, or gateways, which enable them to share data. The world’s most popular WAN is the Internet. Wide Area Network (WAN)  Personal Area Network (PAN) It is a network that is used for communicating among computers and computer devices, including telephones and personal digital assistants, in proximity to an individual’s body. PAN’s can be wired or wireless. Personal Area Network (PAN)  Campus Area Network (CAN) Is an interconnection of local-area networks within a limited geographical space, such as a school campus or a military base.  Network Topology Topology refers to the layout of connected devices on a network. Here, some logical layout of topology: Bus Topology Ring Topology Star Topology Mesh Topology Tree Topology Hybrid Topology Bus Topology Is a network type in which every computer and network device is connected to single cable. Ring Topology It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Star Topology All the computers are connected to a single hub through a cable. The hub is the central node and all others nodes are connected to the center node.  Mesh Topology It is a point-to-point connection to other nodes or devices. All the network nodes are connected to each other. Tree Topology It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. Hybrid Topology It is two different types of topologies which is a mixture of two or more topologies. Physical Components of a Network  Unshielded Twisted-Pair (UTP) ▪ The cable has four pairs of wires inside the jacket. ▪ Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devise. ▪ The EIA/TIA (Electronic Industry Association/ Telecommunication Industry Association) has established standards of UTP and rated six categories of wire. Unshielded Twisted-Pair (UTP)  Unshielded Twisted-Pair (UTP) ▪ UTP Wire Color Coding Orange Green Brown White/Orange White/Green TD+ : Transmit Data Positive value TD- : Transmit Data Negative value RD+ : Receive Data Positive value RD- : Receive Data Negative value The RJ-45 Connector  Shielded Twisted-Pair (STP) ▪ Each pair of wires is individually shielded with foil. ▪ There is a foil or braid shield inside the jacket covering all wires (as a group). ▪ There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).  UTP & STP ▪ Relatively inexpensive. ▪ Technology and standards are fairly Advantages ▪ Easily installed, managed, and proven and stable. reconfigured. ▪ Considerable reduction in EMI. ▪ Basic technology and standards are matured and stable ▪ Only categories 5, 5e and 6 UTP cables ▪ More costlier than UTP and harder to Disadvantages are capable of high-speed data install than UTP and coaxial cables. transmission. ▪ Unsuitable for gigabit speed. ▪ Relatively high rate of attenuation. ▪ Relatively high rate of attenuation. ▪ Sensitive to EMI and eavesdropping.  Fiber-Optic Cables ▪ It consists of two strands. ▪ Each strand has a glass or plastic core surrounded by more glass called cladding. ▪ The center strand provides the wave path while the cladding is composed of reflective glass that refracts light back to the core. ▪ Each strand is covered in a jacket composed of a group of Kevlar fibers for strength, and a reinforcing layer of plastic.  Fiber-Optic Cables ▪ It transmits light rather than electronic signals; eliminating the problem of electrical interference. ▪ It has the ability to transmit signals over much longer distances than coaxial and twisted pair. ▪ Also, it has the capability to carry information at vastly greater speeds. ▪ Two common types: 1.Single mode fiber 2.Multimode fiber  Fiber-Optic Cables ▪ Difference between Single mode and Multimode fibers ▪ High Capacity. ▪ Lesser capacity than Single mode. ▪ More costlier than MM fiber. ▪ Cheaper than SM fiber. ▪ Light pulses are generated by ▪ Light pulses are generated by light injection laser diodes (ILDs). emitted diodes (LEDs). ▪ Can sustain a transmission rate of ▪ Transmission rate of 100 Mbps at 100 Mbps at a distance of 2 distance of 80/90 kilometers. kilometers. ▪ Optimized to allow one light path. ▪ Optimized to allow multi light paths. Principle of Data Communication Basic Data Communication System Defined as the transmission of digital information between two devices using electronic transmission systems. Data will be represented either in the form of electrical signals, electromagnetic waves or light. The source is the device that sends the data message. The transmission medium is the physical path by which a message travels form sender to receiver. The receiver is the device that receives the massage. DTE-Data Terminal Equipment DTE refers to the interface equipment used at the station (between the host and modem) to adapt the digital signals from the computer and terminals to a suitable form for transmission. Examples for DTE: computer, visual monitor, logic controller unit and store buffer. DCE - Data Circuit Equipment DCE means the equipment that converts digital signals to the analog signals and interfaces the data terminal equipment to the analog transmission medium. DCE is a modem (modulator / demodulator). It converts binary digital signals to analog signals  The Network Model OSI and TCP/IP Models What is the OSI model? The Open Systems Interconnection (OSI) model is a conceptual model created by the International Organization for Standardization which enables diverse communication systems to communicate using standard protocols. OSI provides a standard for different computer systems to be able to communicate with each other. The OSI model can be seen as a universal language for computer networking. It’s based on the concept of splitting up a communication system into seven abstract layers.  Why does the OSI model matter? OSI model is still very useful for troubleshooting network problems. Whether it’s one person who can’t get their laptop on the Internet, or a web site being down for thousands of users, the OSI model can help to break down the problem and isolate the source of the trouble. If the problem can be narrowed down to one specific layer of the model, a lot of unnecessary work can be avoided. Each layer of the OSI model handles a specific job and communicates with the layers above and below itself. DDoS attacks target specific layers of a network connection; application layer attacks target layer 7 and protocol layer attacks target layers 3 and 4. This is the only layer that directly interacts with data from the user. Software applications like web browsers and email clients rely on the application layer to initiate communications. But it should be made clear that client software applications are not part of the application layer; rather the application layer is responsible for the protocols and data manipulation that the software relies on to present meaningful data to the user. Application layer protocols include HTTP as well as SMTP (Simple Mail Transfer Protocol is one of the protocols that enables email communications). This layer is primarily responsible for preparing data so that it can be used by the application layer; in other words, layer 6 makes the data presentable for applications to consume. The presentation layer is responsible for translation, encryption, and compression of data. This is the layer responsible for opening and closing communication between the two devices. The time between when the communication is opened and closed is known as the session. The session layer ensures that the session stays open long enough to transfer all the data being exchanged, and then promptly closes the session in order to avoid wasting resources. Layer 4 is responsible for end-to-end communication between the two devices. This includes taking data from the session layer and breaking it up into chunks called segments before sending it to layer 3. The transport layer on the receiving device is responsible for reassembling the segments into data the session layer can consume. The network layer is responsible for facilitating data transfer between two different networks. If the two devices communicating are on the same network, then the network layer is unnecessary. The network layer breaks up segments from the transport layer into smaller units, called packets, on the sender’s device, and reassembling these packets on the receiving device. The network layer also finds the best physical path for the data to reach its destination; this is known as routing. The data link layer is very similar to the network layer, except the data link layer facilitates data transfer between two devices on the SAME network. The data link layer takes packets from the network layer and breaks them into smaller pieces called frames. Like the network layer, the data link layer is also responsible for flow control and error control in intra-network communication (The transport layer only does flow control and error control for inter-network communications). This layer includes the physical equipment involved in the data transfer, such as the cables and switches. This is also the layer where the data gets converted into a bit stream, which is a string of 1s and 0s. The physical layer of both devices must also agree on a signal convention so that the 1s can be distinguished from the 0s on both devices. What is TCP/IP Model? A model designed to standardized computer networking Process of encapsulation What is HTTP? - Hypertext Transfer Protocol HTTP is a protocol which allows the fetching of resources, such as HTML documents. It is the foundation of any data exchange on the Web and it is a client-server protocol, which means requests are initiated by the recipient, usually the Web browser. A complete document is reconstructed from the different sub-documents fetched, for instance text, layout description, images, videos, scripts, and more.  Components of HTTP-based systems is a client-server protocol: requests are sent by one entity, the user-agent (or a proxy on behalf of it). Most of the time the user-agent is a Web browser, but it can be anything, for example a robot that crawls the Web to populate and maintain a search engine index. The user-agent (client) is any tool that acts on the behalf of the user. This role is primarily performed by the Web browser; other possibilities are programs used by engineers and Web developers to debug their applications. The Server, which serves the document as requested by the client. A server appears as only a single machine virtually: this is because it may actually be a collection of servers, sharing the load (load balancing) or a complex piece of software interrogating other computers (like cache, a DB server, or e-commerce servers), totally or partially generating the document on demand. Proxies Processes operating at the application layers are generally called proxies. These can be transparent, forwarding on the requests they receive without altering them in any way, or non-transparent, in which case they will change the request in some way before passing it along to the server. Proxies may perform numerous functions: caching (the cache can be public or private, like the browser cache) filtering (like an antivirus scan or parental controls) load balancing (to allow multiple servers to serve the different requests) authentication (to control access to different resources) logging (allowing the storage of historical information)  FTP (File Transfer Protocol) - is used to communicate and transfer files between computers on a TCP/IP (Transmission Control Protocol/Internet Protocol) network, or the internet. - Users, who have been granted access, can receive and transfer files in the File Transfer Protocol server (also known as FTP host/site). - As a website developer, FTP is used to make changes to a website. Given the large number of files that need to be handled, it is more comfortable and secure to manage them using FTP. List of raw FTP commands ABOR - abort a file transfer. FTP Testing CWD - change working directory. - In cmd DELE - delete a remote file. LIST - list remote files. - C:>ftp MDTM - return the modification time of FTP URL: ftp.dlptest.com or ftp://ftp.dlptest.com/ a file. FTP User: dlpuser MKD - make a remote directory. Password: rNrKYTX9g7z3RgJRmxWuGHbeu. NLST - name list of remote directory. PASS - send password.  SMTP Fundamentals - SMTP is an application layer protocol. The client who wants to send the mail opens a TCP connection to the SMTP server and then sends the mail across the connection. - SMTP is a set of communication guidelines that allow software to transmit an electronic mail over the internet is called Simple Mail Transfer Protocol. - The SMTP server is always on listening mode. As soon as it listens for a TCP connection from any client, the SMTP process initiates a connection on that port (25). - After successfully establishing the TCP connection the client process sends the mail instantly.  TCP (Transmission Control Protocol) - is a standard that defines how to establish and maintain a network conversation through which application programs can exchange data. - TCP works with the Internet Protocol (IP), which defines how computers send packets of data to each other. How Transmission Control Protocol works - TCP is a connection-oriented protocol, which means a connection is established and maintained until the application programs at each end have finished exchanging messages. - It determines how to break application data into packets that networks can deliver, sends packets to and accepts packets from the network layer, manages flow control and because it is meant to provide error-free data transmission, handles retransmission of dropped or garbled packets and acknowledges all packets that arrive.  UDP (User Datagram Protocol) - is a communications protocol that is primarily used for establishing low-latency and loss-tolerating connections between applications on the internet. - It speeds up transmissions by enabling the transfer of data before an agreement is provided by the receiving party. - UDP is beneficial in time-sensitive communications, including voice over Internet Protocol (VoIP), domain name system (DNS) lookup, and video or audio playback. - UDP is an alternative to Transmission Control Protocol (TCP).  The Internet Protocol (IP) - is a protocol, or set of rules, for routing and addressing packets of data so that they can travel across networks and arrive at the correct destination. - Data traversing the Internet is divided into smaller pieces, called packets. - IP information is attached to each packet, and this information helps routers to send packets to the right place. - Every device or domain that connects to the Internet is assigned an IP address, and as packets are directed to the IP address attached to them, data arrives where it is needed.