Computer Networks

: Computer Networks

Computer Network : Computer Network One of the most useful things about computers is their ability to ‘talk’ to each other, when two or more computers are connected together, we call this a network. A computer network is a number of computers linked together to allow them to share resources. 2 Manoj K. CVS Lonavala

Benefits : Benefits Programs can be shared - software packages can be installed onto the file server and accessed by all individual workstations at the same time. This reduces cost, maintenance and makes upgrades easier. You can access your work from any workstation on the network. Very handy if you have to change computer every time you go to a different classroom. Data can be shared by all users at the same time. Many people can access or update the information held on a database at the same time. Thus information is up to date and accurate. Users can communicate with others on the network by sending messages and sharing files. 3 Manoj K. CVS Lonavala

Disadvantages : Disadvantages Networks can be expensive to set up. They often involve taking up floors and ceilings to lay hundreds of feet of cables Networks are vulnerable to security problems. Hackers, disgruntled employees or even competitors might try to break into the system to read or damage crucial information. Much effort is spent preventing unauthorized access to data and software. If the main File Server breaks down, then the whole system becomes useless and no one can carry on working. Malware, such as worms, easily spread on computer networks and not on stand alone computers. Because networks are often complicated, they need expensive expert staff to look after them. 4 Manoj K. CVS Lonavala

Types of Networks : Types of Networks LAN- Local Area Network SAN- Small Area Network MAN- Metropolitan Area Network, and WAN- Wide Area Network It is this ability of different computers to share information which has made the INTERNET possible. The INTERNET is a Wide Area Network. 5 Manoj K. CVS Lonavala

Local Area Network : Local Area Network This include network where the computers are relatively close together. So LANs would be within the same room, a single building or several buildings close together. 6 Manoj K. CVS Lonavala

Local Area Network-Important : Local Area Network-Important LANs use dedicated cables or wireless technology. Each computer connected to a LAN requires a special hardware If the computer is to be connected to a wireless network it will need a wireless adapter. If the computer is to be connected using cables, then a network PCI card is required. 7 Manoj K. CVS Lonavala

Local Area Network : Local Area Network 8 Manoj K. CVS Lonavala

Categories of Computer Network : Categories of Computer Network Peer-to-Peer Networks Client - Server Networks 9 Manoj K. CVS Lonavala

Peer-to-Peer Networks : Peer-to-Peer Networks A peer-to-peer network allows two or more PCs to pool their resources together. Individual resources like disk drives, CD-ROM drives, and even printers are transformed into shared, collective resources that are accessible from every PC. 10 Manoj K. CVS Lonavala

Peer-to-Peer Networks : Peer-to-Peer Networks The advantages of peer-to-peer are: No need for a network administrator Network is fast/inexpensive to setup & maintain Each PC can make backup copies of its data to other PCs for security.  Easiest type of network to build, peer-to-peer is perfect for both home and office use. 11 Manoj K. CVS Lonavala

Client - Server Networks : Client - Server Networks In the client/server network model a computer plays a centralized role and is known as a server all other computers in the network are known as clients. All client computers access the server simultaneously for files, database, docs, spreadsheets, web pages and resources like hard diver, printer, fax modem, CD/DVD ROM and others. In other words, all the client computes depends on the server and if server fails to respond or crash then networking/communication between the server and the client computes stops 12 Manoj K. CVS Lonavala

Client - Server Networks : Client - Server Networks Useful in centralization of data Server- A computer or program which provides services (files, security clearance, access to hardware, etc.) requested by client. computers or programs over a network. Client- A computer or program that requests a service of another computer system or program (the server). 13 Manoj K. CVS Lonavala

Network Topologies : Network Topologies Physical Structure of the Computer Network Star Ring Bus 14 Manoj K. CVS Lonavala

Star Topology : Star Topology The star pattern connects everything to one server, which is the computer that handles the network tasks and holds the data. All communications between computers go through the server. This configuration is good for businesses that have large amounts of rapidly changing data, like banks and airline reservation offices. 15 Manoj K. CVS Lonavala

Star Topology : Star Topology Advantages Gives close control of data. Each PC sees all the data. User sees up-to-date data always. If a computer other than the host fails, no other computer is affected. 16 Manoj K. CVS Lonavala

Star Topology : Star Topology Disadvantages If host computer or its software goes down, the whole network is down. (A backup computer system would be necessary to keep going while repairs are made.) 17 Manoj K. CVS Lonavala

Ring Topology : Ring Topology The ring pattern connects the computers and other devices one to the other in a circle. A central server is not required. Communication flows in one direction around the ring. This configuration is good when the processing of data can be done on the local PC. 18 Manoj K. CVS Lonavala

Ring Topology : Ring Topology Advantages Requires less cabling and so is less expensive 19 Manoj K. CVS Lonavala

Ring Topology : Ring Topology Disadvantages If one node goes down, it takes down the whole network. 20 Manoj K. CVS Lonavala

Bus Topology : Bus Topology The bus pattern connects all the workstations to the same communications line. Communications travels both directions along the line. All the workstations can communicate with each other without having to go through the server. 21 Manoj K. CVS Lonavala

Bus Topology : Bus Topology Advantages Any one computer or device being down does not affect the others 22 Manoj K. CVS Lonavala

Bus Topology : Bus Topology Disadvantages Can't connect a large number of computers this way. It's physically difficult to run the one communications line over a whole building, for example 23 Manoj K. CVS Lonavala

Wide area Network : Wide area Network as 24 Manoj K. CVS Lonavala

Wide area Network : Wide area Network A computer network that crosses geographical boundaries Many small WAN’s can make up a larger WAN The Internet is the biggest WAN as it is comprised of all of the smaller WAN’s and LAN’s in the world connected to the Internet Uses Fiber Optic Cable, Satellite technology, existing TV cable phone lines to send data over the network 25 Manoj K. CVS Lonavala

Wireless Networks : Wireless Networks Wi-Fi -> wireless fidelity Based on the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard Wi-fi is a wireless technology that uses radio frequency to transmit data through the air. 26 Manoj K. CVS Lonavala

Wireless Networks : Wireless Networks A wireless network is any computer network where there is no physical wired connection between sender and receiver, but rather the network is connected by radio waves and/or microwaves to maintain communications.  A hotspot is a public area where users can access the Internet using wireless local area networks (WLAN). 27 Manoj K. CVS Lonavala

Wireless Networks : Wireless Networks The term wireless communication is used for types of communications that do not require a wire for long distance communications. These distances may be short and long. An example of short wireless communication may be a radio remote control. The distance example may be radio signals. When the context is clear the term is often simply shortened to "wireless". There are many devices that use wireless communication. 28 Manoj K. CVS Lonavala

What do you need to do Wi-fi? : What do you need to do Wi-fi? Existing wired network / services (Infrastructure Mode) DHCP/DNS Access point Antennas and bridges Wireless adapter 29 Manoj K. CVS Lonavala

How does Wi-Fi work? : How does Wi-Fi work? Wi-Fi, wireless fidelity, is the wireless technology to handle the networking/communication. Wi-Fi allocates internet / intranet connection globally and to be transmitted by the radio waves. Radio waves are the main cause of Wi-Fi. Radio waves are transmitted from antenna and Wi-Fi receivers pick them up. When a user receives the Wi-Fi signals, a wireless internet / intranet connection is produced and a user is prompted to provide the user name and password if required to establish a wireless connection. 30 Manoj K. CVS Lonavala

Wireless Networks-ADVANTAGES : Wireless Networks-ADVANTAGES Cheaper to set up because you don’t have to buy and install network cable Setup Cost – Reduced cabling required Flexibility – Quick and easy to setup in temp or permanent space Scaleable – Can be expanded with growth Freedom – You can work from any location that you can get a signal Lower total cost of ownership – Because of affordability and low Install cost Allows mobility with laptops, PDA’s smart phones, and PSP’s 31 Manoj K. CVS Lonavala

Wireless Networks-DISADVANTAGES : Wireless Networks-DISADVANTAGES Planning – Depending on the goal Security – Greater exposure to risks Access Compromising Data Denial of Service Speed – Slower than cable Range – Affected by various medium Travels best through open space Reduced by walls, glass, water, etc 32 Manoj K. CVS Lonavala

Types of security ~~ Wi-Fi : Types of security ~~ Wi-Fi Wired Equivalency Privacy (WEP) - WEP encrypts data transmitted over the WLAN A 64-bit WEP encryption is almost always entered by users as a string of 10 Hexadecimal (Hex) characters (0-9 and A-F) A 128-bit WEP encryption is almost always entered by users as a string of 26 Hexadecimal (Hex) characters (0-9 and A-F) 128 bit encryption is more secure because it takes longer to break the passcode because of its increased number of characters. 33 Manoj K. CVS Lonavala

Types of security ~~ Wi-Fi : Types of security ~~ Wi-Fi WiFi Protected Access (WPA) - WPA-PSK is an extra-strong encryption where encryption keys are automatically changed (called rekeying) and authenticated between devices after a specified period of time, or after a specified number of packets has been transmitted. This is called the rekey interval. WPA-PSK is far superior to WEP and provides stronger protection for the home/SOHO user for two reasons. The process used to generate the encryption key is very rigorous and the rekeying (or key changing) is done very quickly. This stops even the most determined hacker from gathering enough data to break the encryption. 34 Manoj K. CVS Lonavala

Types of security ~~ Wi-Fi : Types of security ~~ Wi-Fi Media Access Control (MAC) address filtering - a hardware address that uniquely identifies each node of a network you can identify which nodes have permission to access a network by their individual MAC address. 35 Manoj K. CVS Lonavala

Secure Your Wireless Network : Secure Your Wireless Network Encrypt your traffic Don’t broadcast your SSID. Filter MAC address. Change the default SSID, administrator account, and password. Don’t use an SSID that makes sense to other people Check your antennae Consider AP placement. 36 Manoj K. CVS Lonavala

Network types : Network types Internet - The Internet was created back in 1969, during the Cold War, by the United States military. It was meant to be a "nuke-proof" communications network. Today, the Internet spreads across the globe and consists of countless networks and computers, allowing millions of people to share information. Data that travels long distances on the Internet is transferred on huge lines known collectively as the Internet backbone. The Internet is now maintained by the major Internet service providers such as MCI Worldcom, Sprint, GTE, ANS, and UUNET. Because these providers make huge amounts of revenue off the Internet, they are motivated to maintain consistent and fast connections which benefits everyday Internet users like you and me. 37 Manoj K. CVS Lonavala

Network types : Network types Intranet - Intranet is an internal or private network using Internet technology that can only be accessed within the confines of a company, university, or organization 38 Manoj K. CVS Lonavala

Network types : Network types Extranet - An extranet is a private network that uses Internet technology and the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers, or other businesses. An extranet can be viewed as part of a company's intranet that is extended to users outside the company. 39 Manoj K. CVS Lonavala

Network types : Network types Virtual Private Network (VPN) - A VPN refers to a network that is connected to the Internet, but uses encryption to scramble all the data sent through the Internet so the entire network is "virtually" private. 40 Manoj K. CVS Lonavala

Network types-IMPORTANT : Network types-IMPORTANT The Internet and the World Wide Web are not the same thing. The World Wide Web is the Internet feature that allows you to visit web pages from all over the world. It is one of the many features of the Internet. E-mail, FTP, and Instant Messaging are also features of the Internet. 41 Manoj K. CVS Lonavala

Security : Security The main cause of a security threat is the misuse of the internet without proper anti-virus, anti-spyware. Other causes are: Insiders Network Intrusions Malware and Adware Trojan Horses, Worm E-mail Attachments Floppy Disk, CD and Pen Drive , or Any Infected Computer That Is Attached To The Network. 42 Manoj K. CVS Lonavala

Security : Security A networks greatest strength the ability to share data, is also its greatest weakness. 43 Manoj K. CVS Lonavala

Network Security Issues : Network Security Issues Who has access to the network? Is anti-virus and anti-spyware software installed on all client computers and is it kept up-to-date? Is a Firewall used and is it configured appropriately for the network it protects? Is there a network policy that specifically outlines what is and what is not allowed to be done on the network by the network users? 44 Manoj K. CVS Lonavala

Encryption : Encryption The scrambling of data into unintelligible characters using a key (usually some sort of mathematical transformation). The encrypted file can be restored to its original state (decrypted) using the correct key. Modern encryption methods involve the use of one-way functions (easy to encrypt, very difficult to decrypt) . Such asymmetric encryption involves the sender encrypting with a recipient's public key, which can then only be decrypted by the recipient themselves (the only one with access to the private key). 45 Manoj K. CVS Lonavala

Secure Sockets Layer (SSL) : Secure Sockets Layer (SSL) A protocol, originally by Netscape, designed to give secure communications on the Internet. SSL operates below the application protocols (HTTP, Telnet, FTP, Gopher, etc.) but is layered above the basic TCP/IP protocols so it "protects" the applications that are transmitted over the TCP/IP connection. 46 Manoj K. CVS Lonavala

The Internet : The Internet Internet, intranet and the WWW Features of a web page URL's and hyperlinks The features of web browsers Internet protocols e.g. HTTP, FTP, TCP/IP Cookies Listserv Webcams Internet language and netiquette 47 Manoj K. CVS Lonavala

The Internet : The Internet Bandwidth and its limitations Search engines and their appropriate use e-mail Internet misuse - spam Internet misuse - inappropriate material Ways of blocking access to information Encryption methods Viruses Online services Global databases E-commerce and banking Health Libraries 48 Manoj K. CVS Lonavala

Internet, intranet and the WWW : Internet, intranet and the WWW Intranet - Intranet is an internal or private network using Internet technology that can only be accessed within the confines of a company, university, or organization. Internet- World Wide Web- 49 Manoj K. CVS Lonavala

URL- Uniform Resource Locator : URL- Uniform Resource Locator Uniform Resource Locator, address on the World Wide Web e.g. http://www.cathedral-lonavala.org 50 Manoj K. CVS Lonavala

Hyperlink : Hyperlink Links or references within Web documents that upon selection (clicking the mouse with the cursor located over the document link) cause jumps to another location within the document, to other documents, or to programs that process images, sound, videos, operate upon databases, or perform other functions. Hyperlink objects may be words, phrases, images, or parts of images. Hyperlinked objects are usually displayed in a manner to distinguish them as links. Image maps may not show obvious linked portions and many areas of an image can be linked to different targets. 51 Manoj K. CVS Lonavala

Webpage and Website : Webpage and Website Webpage A document on the World Wide Web. These documents are used with browsers to display text and images and to play sound, video, or animation programs. Web page files contain HTML codes to control the display and playing of their associated components. Website Website is the collection of webpage. 52 Manoj K. CVS Lonavala

Web Browser : Web Browser Web Browser is application software used to browse i.e. used to locate and display Web pages. Most popular web browsers are: Internet Explorer Firefox Apple Safari Opera Google Chrome 53 Manoj K. CVS Lonavala

Protocols : Protocols A high level of coordination is required for the exchange of information between computers on a network. This is provided by a set of rules for information exchange that must be adhered to, by all computers on the network. This set of rules is called a protocol. Protocol is format-rules and regulations, for transmitting data between two devices. 54 Manoj K. CVS Lonavala

Protocols : Protocols File Transfer Protocol (FTP): A protocol used between clients and servers allowing one computer to transfer files to and from another computer over a TCP/IP network. Connections require a user identification which may be open to "guest" or "anonymous" users, or the connections may be restricted to specific persons. The connections may require public passwords, e-mail addresses or secret passwords. Users may be permitted only to download files or they maybe given permission to both upload and download files. 55 Manoj K. CVS Lonavala

Protocols : Protocols Hypertext Transfer Protocol (HTTP): The client-server TCP/IP protocol used on the World-Wide Web for the exchange of HTML documents. Hypertext: A document or set of documents with "links" that aid users in navigating among links and their references. Hypermedia: Like hypertext but includes graphics, sound, video and other kinds of data. 56 Manoj K. CVS Lonavala

Protocols : Protocols TCP/IP 57 Manoj K. CVS Lonavala

Cookies : Cookies A small file used in communication between cooperating programs. Cookies are used by some browsers and Web server programs to identify the client user and even unique preferences or requests from the client user e.g. their user name and password. Cookies may be stored for use during a given session, for a set length of time (seconds, minutes, hours, or days) or retained permanently. Cookie information is stored with the browser on the client side; the information is automatically accessed and used by the browser in subsequent transactions, often without the user's knowledge. 58 Manoj K. CVS Lonavala

Listserv : Listserv An electronic discussion support system. Users can subscribe and unsubscribe by e-mail. All messages sent to the discussion list are automatically sent to all subscribers. Most list servers support archiving of the messages by day, week, month, or year. 59 Manoj K. CVS Lonavala

Webcams : Webcams Webcam is real time camera whose images can be accessed using the WWW, instant messaging or video conferencing software. It will be a digital camera and will upload its images to a web server, either continuously or at regular intervals. Web server is a computer program that receives and processes requests from client browsers. 60 Manoj K. CVS Lonavala

Netiquette : Netiquette Netiquettes Rules of etiquette that apply to Internet communication. 61 Manoj K. CVS Lonavala

Bandwidth : Bandwidth The Bandwidth is the quantity of information that can be transmitted through a communication medium in a given amount of time. 62 Manoj K. CVS Lonavala

Search engines and their appropriate use : Search engines and their appropriate use Search Engine is a program that searches for information on the World Wide Web using key words. Search engines may look only at document titles, headers, or URLs; others may conduct searches of the complete text (full text searches). Web crawler is a specific search engine developed by Brian Pinkerton at the University of Washington. It is a freeware program that "roams” the World Wide Web and collects URLs. Users can then perform searches by entering keywords. 63 Manoj K. CVS Lonavala

Important Terms : Important Terms ASYNCHRONOUS COMMUNICATION Delayed communication, such as that used for newsgroups and mailing lists, where the sender and the recipients don't have to be logged in at the same time. ATTACHMENTS A way to send formatted word processor documents, pictures, and other multimedia files via email. BANDWIDTH The quantity of information that can be transmitted through a communication medium in a given amount of time. Manoj K. CVS Lonavala 64

Important Terms : Important Terms Baud rate The data transfer rate, measured in bits per second-BPS. BLUETOOTH A type of wireless technology that enables mobile phones, handheld computers, and PCs to communicate with each other regardless of operating system. BOUNCE The automatic return of an undeliverable email message to its sender. Manoj K. CVS Lonavala 65

Important Terms : Important Terms BRIDGES Bridge is a device that allows two similar LANs using the same protocol to be interconnected. No modification is made to either the contents or format of the data passing through the device. Bridge usually only has two ports. CHAT ROOM Public real-time teleconference. CLIENT/SERVER MODEL For a local-area network, a hierarchical model in which one or more computers act as dedicated servers and all the remaining computers act as clients. The server fills requests from clients for data and other resources. Manoj K. CVS Lonavala 66

Important Terms : Important Terms COMMUNICATION SOFTWARE Software that enables computers to interact with each other over a phone line or other network. DIGITAL SIGNAL A stream of bits. DIRECT CONNECTION A dedicated, direct connection to the Internet through a LAN, with the computer having its own IP address. DOWNLOAD To copy software from an online source to a local computer. Manoj K. CVS Lonavala 67

Important Terms : Important Terms ELECTRONIC MAIL (EMAIL) Allows Internet users to send mail messages, data files, and software programs to other Internet users and to users of most commercial networks and online services. FIBER-OPTIC CABLE High-capacity cable that uses light waves to carry information at blinding speeds. GATEWAYS Computers connected to two networks that translate communication protocols and transfer information between the two. GLOBAL POSITIONING SYSTEM (GPS) A Defense Department system with 24 satellites that can pinpoint any location on the Earth. Manoj K. CVS Lonavala 68

Important Terms : Important Terms HOST SYSTEM A computer that provides services to multiple users. HUB A network component used to connects computers etc. A HUB does not manage any of the data traffic through it. INSTANT MESSAGING A technology that enables users to create buddy lists, check for buddies who are logged in, and exchange typed messages and files with those who are. INTERNET TELEPHONY (IP TELEPHONY) A combination of software and hardware technology that enables the Internet to, in effect, serves as a telephone network. Internet telephony systems can use standard telephones, computers, or both to send and receive voice messages. Manoj K. CVS Lonavala 69

Important Terms : Important Terms LOCAL AREA NETWORK (LAN) Multiple personal computers connected on a network in a limited geographical area. MAILING LISTS Email discussion groups on special-interest topics. All subscribers receive messages sent to the group's mailing address. MODEM Modulator/demodulator. A hardware device that connects a computer to a telephone line. It converts analog signals into digital signals and vice-versa. NETIQUETTE Rules of etiquette that apply to Internet communication. NETWORK INTERFACE CARD (NIC) Card that adds an additional serial port to a computer. The port is especially designed for a direct network connection. Manoj K. CVS Lonavala 70

Important Terms : Important Terms NETWORK LICENSE License for multiple copies or removing restrictions on software copying and use at a network site. NETWORK OPERATING SYSTEM (NOS) Server operating system software for a local-area network. NEWSGROUPS Ongoing public discussions on a particular subject consisting of notes written to a central Internet site and redistributed through a worldwide newsgroup network called Usenet. You can check into and out of them whenever you want; all messages are posted on virtual bulletin boards for anyone to read anytime. PORT Socket that allows information to pass in and out. Manoj K. CVS Lonavala 71

Important Terms : Important Terms PROTOCOL Protocol is format-rules and regulations, for transmitting data between two devices. REAL-TIME COMMUNICATION Internet communication that enables you to communicate with other users who are logged on at the same time. REMOTE ACCESS Network access via phone line, TV cable system, or wireless link. ROUTERS A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP network. Routers are located at gateways, the places where two or more networks connect. Manoj K. CVS Lonavala 72

Important Terms : Important Terms SERVER A server is a computer that provides resources or services that are shared on the network. A LAN can have more than one server. Each server has a unique name on the network. Dedicated Server- is a server that functions only as a storage area for data and software. In addition, it allows access to hardware resources. File Server- Stores files that LAN computers can access. It also decides on the rights and restrictions that they users need to have while accessing files on the LAN. Printer Server- takes care of the printing requirements of a number of computers. The printer server typically stores the files to be printed on its disk and then executes these requests on a first-in-first-out basis. Modem Server- allows LAN users to share modem. A Proxy Server can allow networked computers to connect to the internet. It can be a major component of a firewall. Manoj K. CVS Lonavala 73

Important Terms : Important Terms SWITCH A switch forwards data packets to computers and printers. TELECOMMUNICATION Long-distance electronic communication in a variety of forms. TELEPHONY Technology that enables computers to serve as speakerphones, answering machines, and complete voice mail systems. UPLOAD To post software or documents to an online source so they're available for others. VIDEO TELECONFERENCE Face-to-face communication over long distances using video and computer technology. Components required for VTC system include- video camera or webcam, microphones, speakers, computer monitor, television or projector VOICEMAIL A telephone-based messaging system with many of the features of an email system. Manoj K. CVS Lonavala 74