A computer network connects independent computers that communicate over a shared network medium. The basic components of a network include at least two computers (servers or clients), networking interface cards, a connection medium like cables, and network operating system software. There are different types of networks including LANs, WANs, intranets, and the Internet. The OSI model defines seven layers of network functionality from the physical layer up to the application layer. TCP/IP is an open networking model used on the Internet with layers including physical, internet, and transport layers.

2. Types of Networks LANs (Local Area Networks) LANs are networks usually confined to a geographic area, such as a single building or a college campus. WANs (Wide Area Networks) Wide area networking combines multiple LANs that are geographically separate Internet The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. Intranet An intranet is a private network utilizing Internet-type tools, but available only within that organization i.e. for large organizations. MANs (Metropolitan area Networks) This refers to a network of computers with in a City. VPN (Virtual Private Network) VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network .

3. OSI Reference Model Seven layers of OSI Model: The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers

4. ISO OSI Layering Architecture

8. Layer 6: Presentation Layer Performs specific functions that are requested regularly by applications Examples: encryption ASCII to Unicode, Unicode to ASCII LSB-first representations to MSB-first representations Layer 7: Application Layer Application layer protocols are application-dependent Implements communication between two applications of the same type Examples: FTP HTTP SMTP (email)

9. Overview of Layers:

13. Local-Area Network Connect computers within a limited physical area such as an office, classroom, or building

14. Wide-Area Network WANs typically connect fewer computers than LANs and normally operate at lower speeds than LANs. WANs, however, provide the means for connecting single computers and many LANs over large distances.

23. Communication Technologies Communication Hardware… Communication Network…

27. Simplex: Information flows in only one direction Half-duplex: Information flows in two directions, but only in one direction at a time. Full-duplex: Information flows in two directions at the same time

28. Basic Signal Terminologies Bit - binary digit, either 0 or 1 Baud - one electronic state change per second Bit rate- a method for measuring data transmission speed (bits/second) Mbps - millions of bits per second (data speed; measure of bandwidth = total information flow over a given time) on a telecommunication medium 8 bits = 1 byte Mb - million bits (quantity of data) MB - million bytes (quantity of data) Gbps - Billion bits per second (data speed) Teraflops - trillion operations per second

29. Data rate - bits per second Bandwidth - bandwidth or signal in cycles per second or hertz Noise - Average level of noise over the communication path. Error rate - rate at which errors occur where error in 1 or 0 bit occurs

34. (Bridge Diagram)

36. Modulation: In a modem, the MODULATION process involves the conversion of the digital computer signals (high/low, on/off or logic 1 and 0 states) to audio-frequency tones. Demodulation: The DEMODULATION process converts the audio tones back into digital signals that a computer can understand directly.

40. When the web server receives this request, it will send the web page back to my computer by breaking it down into smaller parts and sending each part in a packet Part 1 of web page Part 2 of web page 10.11.1.115 208.47.4.80 10.11.1.115 208.47.4.80 To From Payload / Data Packet 1 Packet 2

47. Netiquette & Ethics

52. Web Page: A web Page is a single document written in HTML ( Hypertext Markup Language ) that includes the text of the document, its structure, any links to other documents and graphic images and other media. Homepage: Homepage is a Hypertext document a server will serve as default. URL: A URL is the space of a web browser where the address of a website is written

61. Data Security: Need for Security:

66. Malicious software and antivirus: 1. Malware Commonly, a computer user can be tricked or forced into downloading software onto a computer that is of malicious intent. Such programs are known as malware and come in many forms, such as viruses, Trojan horses, spyware, and worms. 2. Viruses Viruses are programs that can replicate their structures or effects by infecting other files or structures on a computer. The common use of a virus is to take over a computer to steal data. 3. Trojan horse A Trojan horse (commonly known as a Trojan ) is a general term for malicious software that pretends to be harmless so that a user willingly allows it to be downloaded onto the computer.

67. 4. Spyware The term spyware refers to programs that surreptitiously monitor activity on a computer system and report that information to others without the user's consent. 5. Worms Worms are programs that can replicate themselves thoughout a computer network, performing malicious tasks throughout. 6. Botnet A botnet is a network of "zombie" computers that have been taken over by a "bot" that performs large-scale malicious acts for the creator of the botnet.

70. Tier Architecture of Client Server model: 2-Tier Architecture : 2-tier architecture is used to describe client/server systems where the client requests resources and the server responds directly to the request, using its own resources. This means that the server does not call on another application in order to provide part of the service.

72. Multi-Tiered Architecture :

73. WWW Definition: All the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP) History: 1969 - RFCs begun by S. Crocker 1972 - Email by Ray Tomlinson & Larry Roberts 1970’s - TCP by Vint Cerf & Bob Kahn 1980s – Hardware Explosion (LANs, PCs, and workstations) 1983 – Ethernet by Metcalfe 1985 – Internet used by researchers and developers

75. Model diagram of WWW: CGI User C L I E N T HTTP TCP/IP SERVER Docs