Internet Applications

World Wide Web

The World Wide Web (abbreviated as WWW or W3^[2] and commonly known as the Web), is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them viahyperlinks. Using concepts from earlier hypertext systems, British engineer and computer scientist Sir Tim Berners-Lee, now living in Lexington, MA as the Director of the World Wide Web Consortium, wrote a proposal in March 1989 for what would eventually become the World Wide Web.^[1] At CERN in Geneva, Switzerland, Berners-Lee and Belgian computer scientist Robert Cailliau proposed in 1990 to use "HyperText ... to link and access information of various kinds as a web of nodes in which the user can browse at will",^[3] and publicly introduced the project in December.^[4]

"The World-Wide Web was developed to be a pool of human knowledge, and human culture, which would allow collaborators in remote sites to share their ideas and all aspects of a common project."^{[5];from wikipedia}

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. Examples of Web browsers: Internet Explorer, Netscape Navigator, Opera, Safari, Godzilla

A web search engine is designed to search for information on the World Wide Web and FTP servers. The information may consist of web pages, images, information and other types of files. Example of search engines: Yahoo, Google, Alta Vista, Hot Bot

Internet Relay Chat

Internet Relay Chat (IRC) is a form of real-time Internet text messaging (chat) or synchronous conferencing.^[1] It is mainly designed for group communication in discussion forums, called channels,^[2]but also allows one-to-one communication via private message^[3] as well as chat and data transfer,^[4] including file sharing.^[5]

IRC was created in 1988. Client software is now available for every major operating system that supports Internet access.^[6] As of April 2011, the top 100 IRC networks served more than half a million users at a time,^[7] with hundreds of thousands of channels^[7] operating on a total of roughly 1,500 servers^[7] out of roughly 3,200 servers worldwide.

History

IRC was created by Jarkko Oikarinen in August 1988 to replace a program called MUT (MultiUser Talk) on a BBS called OuluBox in Finland.^[9] Oikarinen found inspiration in a chat system known asBitnet Relay, which operated on the BITNET.^[9]

IRC was used to report on the 1991 Soviet coup d'état attempt throughout a media blackout.^[10] It was previously used in a similar fashion during the Gulf War.^[11] Logs of these and other events are kept in the ibiblio archive.^[12]

[edit]Technical information

A Screenshot of XChat, a cross-platformIRC client.

Xaric, a text-based IRC client, in use onMac OS X. Shown are two IRC channels and a private conversation with the software author.

IRC is an open protocol that uses TCP^[1] and optionally TLS. An IRC server can connect to other IRC servers to expand the IRC network.^[13] Users access IRC networks by connecting a client to a server.^[14] There are many client implementations such as mIRC or XChat and server implementations, e.g. the original IRCd. Most IRC servers do not require users to register an account but a user will have to set a nickname before being connected.^[15]

IRC was originally a plain text protocol^[1] (although later extended), which on request was assigned port 194/TCP by IANA.^[16] However, the de facto has always been to run IRC on 6667/TCP^[17] and nearby port numbers (for example TCP ports 6660-6669, 7000)^[18] to avoid having to run the IRCd software withroot privileges.

The protocol specified that characters were 8-bit but did not specify the character encoding the text was supposed to use.^[19] This can cause problems when users using different clients and/or different platforms want to converse.

All client-to-server IRC protocols in use today are descended from the protocol implemented in the irc2.4.0 version of the IRC2 server, and documented in RFC 1459. Since RFC 1459 was published, the new features in the irc2.10 implementation led to the publication of several revised protocol documents (RFC 2810, RFC 2811, RFC 2812 and RFC 2813); however, these protocol changes have not been widely adopted among other implementations.^{[citation needed]}

Although many specifications on the IRC protocol have been published, there is no official specification, as the protocol remains dynamic. Virtually no clients and very few servers rely strictly on the above RFCs as a reference.^{[citation needed]}

Microsoft made an extension for IRC in 1998 via the proprietary IRCX.^[20] They later stopped distributing software supporting IRCX, instead developing the proprietary MSN .NET Messenger Service.

New protocol IRCwx (IRC web extension) inspired by IRCX is made by net-bits.net in an attempt to modernize IRCX for web use.^[21]

The standard structure of a network of IRC servers is a tree.^[22] Messages are routed along only necessary branches of the tree but network state is sent to every server^[23] and there is generally a high degree of implicit trust between servers. This architecture has a number of problems. A misbehaving or malicious server can cause major damage to the network^[24] and any changes in structure, whether intentional or a result of conditions on the underlying network, require a net-split and net-join. This results in a lot of network traffic and spurious quit/join messages to users^[25] and temporary loss of communication to users on the splitting servers. Adding a server to a large network means a large background bandwidth load on the network and a large memory load on the server. Once established however, each message to multiple recipients is delivered in a fashion similar to multicast, meaning each message travels a network link exactly once.^[26] This is a strength in comparison to non-multicasting protocols such as Simple Mail Transfer Protocol (SMTP) or Extensible Messaging and Presence Protocol (XMPP).

See also: IRC daemon

[edit]Commands and replies

Main article: List of Internet Relay Chat commands

IRC is based on a line-based structure with the client sending single-line messages to the server,^[27] receiving replies to those messages^[28] and receiving copies of some messages sent by other clients. In most clients users can enter commands by prefixing them with a '/'. Depending on the command, these may either be handled entirely by the client, or (generally for commands the client does not recognize) passed directly to the server, possibly with some modification.^{[citation needed]}

Due to the nature of the protocol automated systems cannot always correctly pair a sent command with its reply with full reliability and are subject to guessing.^[29]

[edit]Channels

The basic means of communicating to a group of users in an established IRC session is through a channel.^[30] Channels on a network can be displayed using the IRC command LIST^[31] that lists all currently available channels on that particular network.

Users can join to a channel using the JOIN command,^[32] in most clients available as /join #channelname. Messages sent to the joined channels are then relayed to all other users.^[30]

Channels that are available across an entire IRC network are prepended with a '#', while those local to a server use '&'.^[33] Other non-standard and less common channel types include '+' channels—'modeless' channels without operators —^[34] and '!' channels, a form of timestamped channel on normally non-timestamped networks.
get from wikipedia.org

Wireless Technologies

• Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 48 km (30 miles) apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.

• Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 35,400 km (22,200 miles) (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.

• Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.

• Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.

• Infrared communication can transmit signals between devices within small distances of typically no more than 10 meters. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.

• A global area network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.

get from wikipedia

Wired Technologies

• Twisted pair wire is the most widely used medium for telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer networking cabling (wired Ethernet as defined by IEEE 802.3) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are rated in categories which are manufactured in different increments for various scenarios.

• Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.

• ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

• Optical fibre cable consists of one or more filaments of glass fiber wrapped in protective layers that carries data by means of pulses of light. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire. This capacity may be further increased by the use of colored light, i.e., light of multiple wavelengths. Instead of carrying one message in a stream of monochromatic light impulses, this technology can carry multiple signals in a single fiber.

Exotic technologies

There have been various attempts at transporting data over more or less exotic media:

• IP over Avian Carriers was a humorous April fool's Request for Comments, issued as RFC 1149. It was implemented in real life in 2001.

• Extending the Internet to interplanetary dimensions via radio waves.

A practical limit in both cases is the round-trip delay time which constrains useful communication.

Computer-Networks

A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices. Computer networking or Data communications (Datacom) is the engineering discipline concerned with the computer networks. Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications, computer science, information, technology and/or computer engineering since it relies heavily upon the theoretical and practical application of these scientific and engineering disciplines.

Networks may be classified according to a wide variety of characteristics such as medium used to transport the data, communications protocol used, scale, topology, organizational scope, etc.

A communications protocol defines the formats and rules for exchanging information via a network. Well-known communications protocols are Ethernet, which is a family of protocols used in LANs, the Internet Protocol Suite , which is used not only in the eponymous Internet, but today nearly ubiquitously in any computer network.

Study Tips

"One way to study is to sing the information. Another way is to think that the information you want to study is written in your mind in different colors. If you make a cover of your favorite magazine for your text book you will pay more attention to your textbook."

Avoid all distractions and don't study when you are tired. Relax with something light and then come back to study. Don't confuse laziness with tiredness.

1. Have a time table for better focus; 2.Study for a stretch of one hour each session and take breaks; 3.Write or jot notes. What is written can sometimes be easliy remembered; 4.Write a summary of the passage or chapter to reinforce better understanding; 5.Test yourself on a few questions to check understanding. This will reveal parts of a passage or chapter where more time should be spent or where your notes need revision; 6.Last but not least, studying is hard work. Hence, be prepared to work hard. No worthy certificate or qualification will come easily.

Think positively about studying, be goal directed, know what you want at the end of the day, know your deadlines, and take practice tests to help you understand what you have studied.

Ask your teachers questions. I ask questions in class whenever I don't understand something. This does two things. First, I get the help I need. Second, it shows the teacher that I'm interested and trying. You want your teachers to have a good opinion of you. It can help your grade.