Computers Basics

Just getting started with technology? Here are courses designed especially for adults who are new to technology. They provide a solid introduction to computers and will help prepare you for the more advanced courses we offer.
Introductory Classes
Quick Keyboarding
Quick Keyboarding - Advanced
Getting Started with Computers
Computer & Internet Safety for Adults & Kids
How Computers Work: Inside and Out
Windows
Windows Introduction
Windows System Tools

How to Use Computer Management on the Local Computer

Computer Management Overview
Computer Management is a collection of Windows administrative tools that you can use to manage a local or remote computer. The tools are organized into a single console, which makes it easy to view administrative properties and to gain access to the tools that are necessary to perform your computer-management tasks.

The Computer Management Console
The Computer Management console consists of a window divided into two panes. The left pane contains the console tree; the right pane contains details. When you click an item in the console tree, information about that item is displayed in the details pane. The information that is displayed is specific to the item that you select.

The administrative tools in Computer Management are grouped into the following three categories in the console tree: • System Tools
• Storage
• Services and Applications



Each category includes several tools or services.
System Tools• Event Viewer

Use the Event Viewer tool to manage and view events that are recorded in the Application, Security, and System logs. You can monitor the logs to track security events and to identify possible software, hardware, and system problems.
• Shared Folders

Use the Shared Folders tool to view connections and resource in use on the computer. You can create, view, and manage shares, view open files and sessions, and close files and disconnect sessions.
• Local Users and Groups

Use the Local Users and Groups tool to create and manage your local user accounts and groups. Local Users and Groups is available only in Windows XP Professional.
• Performance Logs and Alerts

Use the Performance Logs and Alerts tool to configure performance logs and alerts to monitor and collect data about your computer's performance.
• Device Manager

Use Device Manager to view the hardware devices installed in your computer, update device drivers, modify hardware settings, and troubleshoot device conflicts.

Storage• Removable Storage

Use the Removable Storage tool to track your removable storage media and manage the libraries, or data-storage systems, that contain them.
• Disk Defragmenter

Use the Disk Defragmenter tool to analyze and defragment volumes on your hard disks.
• Disk Management

Use the Disk Management tool to perform disk-related tasks such as converting disks or creating and formatting volumes. Disk Management helps you manage your hard disks, and the partitions or volumes that they contain.

Services and Applications• Services

Use Services to manage services on local and remote computers. You can start, stop, pause, resume, or disable a service.
• WMI Control

Use WMI Control to configure and manage the Windows Management Instrumentation (WMI) service.
• Indexing Service

Use Indexing Service to manage the Indexing service, and to create and configure additional catalogs to store index information.

NOTE: The actual set of tools and services that is listed in Computer Management depends on the services that are installed on the host computer.


 
How to Use Computer Management on the Local Computer


NOTE: You must be logged on as Administrator or as a member of the Administrators group view and modify most properties and perform most computer-management tasks.

To start and use Computer Management on the local computer: 1. Click Start, and then click Control Panel. Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management.

The Computer Management window for the local computer is displayed. "Computer Management (Local)" is displayed at the root of the console tree.
2. In the console tree, expand System Tools, Storage, or Services and Applications to view the tools and services in each of these containers.
3. Click the item that you want (for example, Event Viewer) to use the tool, and then view the information that is associated with it.


 
How to Use Computer Management on a Remote Computer

NOTE: You must be logged on as Administrator or as a member of the Administrators group to view and modify most properties and perform most computer-management tasks.

To connect to and use Computer Management on another computer: 1. Click Start, and then click Control Panel. Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management.
2. Right-click Computer Management (Local), and then click Connect to another computer.
3. Click Another Computer, and then type the name of the computer that you want to manage remotely, or click Browse to locate the computer. Click OK and then click OK to return to the Computer Management window. The Computer Management window of the remote computer is displayed. The name of the remote computer is displayed at the root of the console tree.
4. In the console tree, expand System Tools, Storage, or Services and Applications to view the tools and services in each of these containers.
5. Click the item that you want (for example, Event Viewer) to use the tool, and then view the information that is associated with it.


How to Use Help in Computer Management

To use Computer Management Help or to use the Help files for any of the individual administrative tools that are contained in Computer Management: 1. Start Computer Management.
2. Use either of the following steps: • In the console tree, right-click the item that you want (for example, Computer Management or Device Manager), and then click Help.
• Click the item in the console tree (for example, Device Manager or Computer Management), and then click Help on the Action menu.

What is the most efficient way to find information about computer security?

It is generally agreed upon by those who spend a lot of time online that Google (»www.google.com/) is the grandmaster of all search tools. While doing pretty much anything in Google will get you decent results, there are a few things you can do to make your experience even better.

Tips:
Word order matters. Put the most pertinent search terms first.

Repetition matters. Entering a particular search term multiple times will, at the very least, change the order of your results. In general, the term with multiple instances (and therefore more weight) will be more prevalent in the search results.

Case does not matter. Don't spend extra effort on capitalizing -- it's ignored by Google completely.

Use quotes when looking for exact phrases; otherwise, use multiple separate words.
"opportunities multiply as they are seized"

The Google Toolbar (»toolbar.google.com/) is an invaluable tool that grants you Google's powers without having to go to the site each time you need to find something. Also, when Google toolbar is installed, highlight any text on a webpage (double-click it if it's a single word) and right click it. Select "Google Search," and Google will search for that text and return you the results.
Using the advanced features of the toolbar requires that you send information about the pages you are viewing to Google. Be sure to disable the advanced features if this is an issue for you.
Do not include words like "a," "to" and "the" in your queries; they are omitted by Google because of how common they are, and they don't help your search in any way. If you really want to use one, add a '+' (plus) to it, and it will force Google to include it in the query. Also, when using quotes to search for phrases, these words are not omitted; the entire phrase you entered within the quotes is searched for.

By default, Google uses the Boolean AND operator when performing searches when given multiple arguments. In other words, if you enter two words into Google and hit enter, it will search for pages that have both of the words in them, not one or the other.

You can use 'OR' to search instead of the default 'AND' by putting an 'OR' between search terms.
You can also use '|' (the pipe character) as OR.
house OR car
cat | dog

When you perform a query and get your results back, the blue bar located under the search tabs will say, "Searched _ pages for *your_terms." If *your_term* was a word with a definition at dictionary.com, the word *your_term* will be a link to the definition of the word at dictionary.com.

You can group search terms using both the default 'AND' and the 'OR' operations together.
cats (pets OR wild)
plants green (ocean | land)

It is possible to remove results that contain certain words by using the '-' (minus) sign. This allows you to filter out results that you know don't pertain to what you are looking for.
ford mustang -horse

You can use an '*' (asterisk) as a full-word wildcard in a phrase lookup. This is helpful when you want to fill in gaps in a search phrase with any full word.
"rule of *"

Can use 'intitle:' to find things that exist only in the title of web pages.
intitle:technology

Can use 'inurl:' to find things that exist only in the url of a web page.
inurl:education

Can use 'intext:' to find things that exist only in the body of a web page.
intext:"sleep disorders"

Can use 'inanchor:' to find things that exist only in the anchor of a web page. An anchor is the text associated with a link that helps to identify it.
inanchor:daycare OR babysitter

Can use 'site:' to isolate a search to just a certain website or domain. This, by the way, is a far better way to search the Microsoft site than using their built-in search feature.
site:microsoft.com "securing windows 98" (good luck)

Can use 'link:' to find all pages that link to a given site:
link:slashdot.org

Can use 'cache:' to find the cached version of a certain site. A cache is a snapshot copy of the site that is helpful if the site is offline or changed from when you saw it last.
cache:www.cnn.com

Can use 'filetype:' to find various file types that exist on the Internet. This is very powerful when combined with other search options.
filetype:ppt "nursing education"

Can use 'related:' to find pages that are related in type/classification to the input given. For example, 'related:www.slashdot.org' will yield hits like www.userfriendly.org because they are both "geek-oriented."
related:www.securityfocus.com

Can use 'info:' to get all Google-related information (cache, stocks, links, related, etc.) about a given site.
info:www.microsoft.com

Can use 'phonebook:' to find phone number and address information about people and businesses. This very powerful feature will find phone numbers when given a name and state abbreviation. To get more specific, just add the city to the query as well. There are three different phonebook related searches available - phonebook, rphonebook and bphonebook. The first searches the whole phonebook directory, the second only residential entries and the third only businesses.
phonebook:smith ca
rphonebook:smith fremont
bphonebook:round table, fremont

Efficient computer tools: what would you put on the list?

What tools do you use to be efficient while working on a computer, be it online or not? Things like del.icio.us, dropload, winzip, phpbboards, group blogs/wikis, etc. Are there any books for general fine tuning of already computer-familiar users? What about seminars?

I was thinking about everyday things people do to speed up their work - like, not everyone uses alt+tab, for example, to switch between app windows. I was also thinking about how to travel as lightly as possible business wise - so, if all your data & tools are stored online, it's just you and the suitcase. I know this is probably a cloudy question, but I know you guys can help me clarify. :D

Teletraffic engineering in broadband networks

Teletraffic engineering is a well-understood discipline in the traditional voice network, where traffic patterns are established, growth rates can be predicted, and vast amounts of detailed historical data are available for analysis. However, for modern broadband networks, the teletraffic engineering methodologies used for voice networks no longer suffice. Various aspects relating to teletraffic engineering in broadband networks are discussed in this article.

Firstly, the nature of broadband traffic is different from that of traditional voice networks. Many of the methodologies developed for traditional networks were based on the nature of voice calls, and are therefore not applicable to broadband networks. The nature of broadband traffic (broadband traffic characteristics) is discussed in the following sub-section.

The inherent nature of broadband networks is also different from that of traditional voice networks. Broadband networks have:

* high speeds,
* small cell sizes (in ATM networks), and
* limited information in the header.

These factors make teletraffic engineering in broadband networks more difficult than in traditional voice networks. A few more factors that further complicate teletraffic engineering in broadband networks are:

* A wide range of applications with diverse Quality of Service (QoS) requirements must be catered for.
* Much of the traffic (e.g., voice, video) is not amendable to flow control.
* The feedback within the network is “slow”.
* There are a large variety of traffic patterns (see long-tail traffic).

Network Centrics

Network Centrics is the emerging discipline of applying and enhancing networking and computing concepts and implementation technologies in a variety of social, business, content distribution, and communication domains involving interactions amongst the domain entities. Network Centrics acts as a catalytic agent resulting in significant improvements in the definition, modeling, comprehension, performance, and effectivity associated with these interactions. This topic has gained importance because of increasing connectivity at individual, corporate, and government levels. Network Centrics is supported by a sustained growth of Internet in conjunction with continued advances in efficient computing algorithms, cost- solutions, and high-performance options that can now be leveraged in a variety of domains.

Overview

Network Centrics focuses on the central role of integrated networking and computing as a premise, facilitator, and accelerator for a rapid, sustained, cost-effective and managed improvement of interactions among the various entities constituting a domain. It formalizes, automates, and extends the fundamental concept of network effect that describe the underlying connectivity among large number of entities in a wide variety of fields ranging from social groups, electrical transmission systems, spread of pandemics, metabolic pathways, gene expression, evolutionary behavior, and various Internet based large applications. Closely associated with such fundamental network connectivity is the popular concept of six degrees of separation (that all human beings are on the average only six acquaintances away from any other human being in the world) that is now part of common vernacular.

Improving Interactions among the Domain Entities

Underlying connectivity among the entities which are spatially or temporally separated from other entities is severely inefficient, thus limiting the network effect for the associated interactions. The network effect can be improved by using an automated information infrastructure as a substratum for bridging geographical and temporal distances in a fast, reliable, and secure fashion. Networking infrastructures have evolved from smoke and light signals, telegraphs, telephones, mobile telephony, to Internet applications leveraging key advances in electro-mechanical transducers, semiconductor, magnetic data storage, software programmed computers, wireless communication, and algorithms. Although technologies such as computer hardware and software have been critical in the growth of digital data and telephony networks, the two broad fields of networking and computing have evolved independently, thus limiting their potential in certain domains. Network Centrics consolidates the principles, tools, and technologies of the networking and computing fields for a unified approach towards improving domain interactions.

The meteoric rise of social networking web sites such as My Space and Facebook has demonstrated the power of networking (fast connections for large number of users) and computing technologies (databases, search algorithms, matching algorithms, user interface). Such an infrastructure serves as a potent catalyst which can improve connectivity and improve associated interactions with several orders of magnitude. Another application of the Network Centrics concepts is exemplified by a mature and scalable trading platform provided by Internet auction sites such as eBay that efficiently interconnects the buyers and sellers across geographical and temporal boundaries. This Network Centric platform requires efficient implementation of auction algorithms, databases for storing goods and current bids and email software for automatic notifications used to improve the auction process all working over a large area data network. An extensive use of both computing and networking technologies enables a reliable, transparent, secure and well defined way of millions of interactions on a daily basis for a large number of participants interested in finding and buying specific physical goods on the one hand and sellers on the other who have profit making objectives. This is in stark contrast with the local bazaars of yesteryears with at most hundreds of people participating in handful of auctions in a session.

Besides these recent Internet phenomena, now part of the day-to-day life in all continents and most countries, there is also a profound change in the role of networking for national defense. Many large countries, led by United States, have unequivocally stipulated that the current defense strategy should be radically transformed with information networking being the central substratum for command, control, intelligence, sensing, and reconnaissance. The scope of such network-centric warfare goes far beyond policy, directives, training, and logistics to actual remote real-time sensing and shooting. This involves a robust, secure and comprehensive integration among all sensor integration, data collection, data storage, information analysis, decision making, and weapon system activation tasks across large geographical distances and multiple services and coalition partners. In fact, the term Network Centricity itself has emerged from the set of many policy documents, starting with Adm. William Owens introduction of the term “system of systems” followed by Network Centric Warfare as discussed by Vice Admiral Arthur Cebrowski and John Gartska, and detailed in the book “Network Centric Warfare”). Netcentric approach is a now a key facet of the strategic transformation of US defense forces with information superiority.

Extending Basic Networking Concepts

Network Centrics extends the fundamental concept of domain networking that exists, though in a constrained fashion, independent of any automation provided by information (computing and networking) infrastructure. This extension is initiated by adding specific networking concepts such as addressing, routing, multicast, persistence, robustness, and assurance. This is further enriched by leveraging computing concepts such as discovery, mediation and search, collaboration, filtering and data mining algorithms with associated automated implementations using computer and software technologies. Adequate sensor and actuator components are used to interface the domain entities with the underlying automation infrastructure. The use of service level agreements for interactions ensures quality of service, for a specific price, and associates information assurance for privacy, authenticity, and non-repudiation. These technical concepts are well understood and widely implemented with a large number of technologies as epitomized by existing information automation infrastructures (networks). This includes the Internet with TCP/IP and HTTP family of protocols and the mobile communications devices based on GSM and CDMA standards providing voice, email, paging, and other applications. The implementation of these infrastructural networks has been possible with extensive research and development over the past four decades in packet networking, mobile cellular architectures, computing algorithms, point and click user interfaces, data processing techniques and Internet web applications. Though landline phone networks have been around for more than a hundred years and at least initially played a major role in accessing Internet with dialup connections, their importance is diminishing rapidly because of their inherent efficiency, cost, and flexibility issues.

Studying and organizing the interactions among domain entities can be facilitated by judiciously applying one or more networking concepts such as queuing theory and computer simulation techniques. For any performance improvement, however, automated technologies such as wide area communication, algorithmic manipulation, and persistent storage of data in transit, bring us from basic and simple networking to the field of Network Centrics. The use of appropriate sensor technologies which can transform many chemical, biological, physical, and situational data into electrical signals facilitate linking with data collection networks for further information aggregation, processing, knowledge mining, and decision making. Today it is mostly the computer and network technologies manifested in well known products such as computer servers, PC, web browsers, database management system, email, paging, data mining tools, TCP/IP protocols, routers, optical communication links, mobile PDA, etc. that are deployed for a network centric performance boosting for interactions occurring over large distances and time scales. Besides these widely deployed computing and data network technologies, there are other emergent technologies that are also relevant for Network Centric improvement of domain interactions.

Disadvantages of Computer

It’s very common today to use the computer. However protecting our selves from the people who want to attack our PC’s is very important to us. There are some people; they are called self-Hackers, who can steal your identity information or personal information by going through your Internet connection. Even if you clear your browser history the information can be retrieved in seconds. There are a lot of disadvantages and advantages to using the computer in these days; computers make our lives easy, but we see that we buy expensive equipment for this easier life. There are a lot of disadvantages found with computer in these days.

New Computer Inventions

New inventions are everyday occurrences in the computer world. As a matter of fact, a month ago, Stealth Ideas Inc., introduced the StealthSurfer II ID Protect. It is a miniature flash drive that lets you surf the Internet anonymously from your computer using an encrypted mode. It comes with memory of 256 megabytes to two-gigabytes and prices start at $99. For those who dabble in the arts, the DigiMemo-692 Digital Notepad enables you to record sketches with ink and paper and then syncronize your notes into your PC using any handwriting reorganization software.

Handheld devices such as PDA or Pocket PC is best for note sketching and it can be synchronized into your PC as a digital copy. The problem of the handheld is its screen input limitations and the screen protector needs to be replaced frequently. DigiMemo 692 Digital Notepad is a breakthrough to all these limitations which is able to 'record' your sketches with ink and ordinary paper. You can easily synchronize your notes into your PC and it is compatible with most of the handwriting reorganization software. This handy device will record your notes, ideas and sketches without the need to scan, and it comes with ink cartridge, a digital pen and software. It also comes with a USB cable that is compatible with WIN 2000 and XP.

The Microsoft Xbox 360 is one of the latest inventions of video games. Video game lovers everywhere are rejoicing the arrival of the new system. The newest Xbox is still a gamer's dream, but it is also being marketed as a media center. Not only can the system be used for playing video games, but it can also be used to play DVDs, CDs and MP3s. Digital cameras can be hooked up to it, as well as mp3 players and even personal computers.

Patenting computer and related inventions come under the intellectual property rights of different countries, where the ownership and copy rights are reserved to the person or organization who invented the product. But in the United States, computer hardware or software invention are deemed patentable only if the invention is vital to a particular task or process. In short, patents are not given to software or even hardware, that are extensions to existing computer technology or if it's just a method of doing business.

One of the new computer inventions is patented by IBM and this is a tiny hard drive the size of a fifty cent piece. This small chip like thing can store up to 340 MB of data and will be very useful in mobile devices, digital cameras, music players, etc.

computers

Nobody thought 20 years ago that the computer would change our lives. It’s amazing how computers can change it. These days, the computer is the most important thing in this life; computer has became a daily thing for the human being. Computers makes our lives easy. In the past the life was kind of hard; no computer, that means a lot of hand work, a lot of wasted time. For example, in the past if you wanted to take some money from the bank, you had to go stand in a long line in a branch and wait to take some money out or deposit money into your account. When the computers came, life definitely changed; it became easier;in a few seconds you can get what you want.

Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").


Network Interface Cards
Main article: Network card

A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.


Repeaters

Main article: Repeater

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.

Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the Physical layer, the first layer of the OSI model.



Hubs

Main article: Network hub

A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. [5]

Bridges
Main article: Network bridge

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do. but learns which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:
Local bridges: Directly connect local area networks (LANs)
Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs.


Switches
Main article: Network switch

A switch is a device that does switching, that is it forwards and filters OSI layer two datagrams (chunk of data communication) between ports (connected cables) based on the Mac-Addresses in the packets.[6] This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports with the intention that most or all of the network be connected directly to a switch, or another switch that is in turn connected to a switch. [7]

"Switches" is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.




Routers
Main article: Router

Routers are the networking device that forward data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812) This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home use, have been integrated with routers to allow multiple home computers to access the Internet.

Computer Networks

A computer network is an interconnection of a group of computers. Networks may be classified by what is called the network layer at which they operate according to basic reference models considered as standards in the industry such as the four-layer Internet Protocol Suite model. While the seven-layer Open Systems Interconnection (OSI) reference model is better known in academia, the majority of networks use the Internet Protocol Suite (IP) as their network model.

By scale:

Computer networks may be classified according to the scale: Personal area network (PAN), Local Area Network (LAN), Campus Area Network (CAN), Metropolitan area network (MAN), or Wide area network (WAN). As Ethernet increasingly is the standard interface to networks, these distinctions are more important to the network administrator than the end user. Network administrators may have to tune the network, based on delay that derives from distance, to achieve the desired Quality of Service (QoS). The primary difference in the networks is the size.

Controller Area Networks are a special niche, as in control of a vehicle's engine, a boat's electronics, or a set of factory robots

By connection method

Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as Optical fiber, Ethernet, Wireless LAN, HomePNA, or Power line communication.

Ethernets use physical wiring to connect devices. Often, they employ the use of hubs, switches, bridges, and routers.

Wireless LAN technology is built to connect devices without wiring. These devices use a radio frequency to connect.

By functional relationship (Network Architectures)

Computer networks may be classified according to the functional relationships which exist between the elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup) architectures.

By network topology

Main article: Network Topology

Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc.

Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout.


By protocol

Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information. For a development of the foundations of protocol design see Srikant 2004 [1] and Meyn 2007

Introduction to Network Types

LAN, WAN and Other Area Networks

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:

1. LAN - Local Area Network
2. WLAN - Wireless Local Area Network
3. WAN - Wide Area Network
4. MAN - Metropolitan Area Network
5. SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
6. CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
7. PAN - Personal Area Network
8. DAN - Desk Area Network

LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.

Note that these network types are a separate concept from network topologies such as bus, ring and star.
See also - Introduction to Network Topologies
LAN - Local Area Network
A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.
WAN - Wide Area Network
As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.
LAN, WAN and Home Networking
Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.
Other Types of Area Networks
While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:
Wireless Local Area Network - a LAN based on WiFi wireless network technology
Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.


In detail

Personal Area Network (PAN)

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs or scanners. The reach of a PAN is typically within about 20-30 feet (approximately 6-9 Meters). PANs can be used for communication among the individual devices (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).

Personal area networks may be wired with computer buses such as USB[3] and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.



Local Area Network (LAN)

A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) connect to the internet. All of the PCs in the library are connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnection devices and eventually connect to the internet. The cables to the servers are on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbps.

The staff computers (bright green) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.
Typical library network, in a branching tree topology and controlled access to resources

All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbps Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

The staff have a VoIP network that also connects to both the Internet and the academic network. They could have paths to the central library system telephone switch, via the academic network. Since voice must have the highest priority, it is on the pink network. The VoIP protocols used, such as RSVP, are virtual circuits rather than connectionless forwarding paths.

Depending on the circumstance, the computers in the network might be connected using cables and hubs. Other networks might be connected strictly wirelessly. It depends on the number of PCs that you are trying to connect, the physical layout of your workspace, and the various needs of network. Not shown in this diagram, for example, is a wireless workstation used when shelving books.

The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. Inverse multiplexing is commonly used to build a faster aggregate from slower physical streams, such as bringing 4 Gbit/s aggregate stream into a computer or network element with four 1 Gbit/s interfaces.


Campus Area Network (CAN)


Main article: Campus Area Network

A network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base. A CAN, may be considered a type of MAN (metropolitan area network), but is generally limited to an area that is smaller than a typical MAN.

This term is most often used to discuss the implementation of networks for a contiguous area. For Ethernet based networks in the past, when layer 2 switching (i.e., bridging (networking) was cheaper than routing, campuses were good candidates for layer 2 networks, until they grew to very large size. Today, a campus may use a mixture of routing and bridging. The network elements used, called "campus switches", tend to be optimized to have many Ethernet-family (i.e., IEEE 802.3) interfaces rather than an arbitrary mixture of Ethernet and WAN interfaces.

Metropolitan Area Network (MAN)
Main article: Metropolitan Area Network

A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN.


Wide Area Network (WAN)
Main article: Wide Area Network

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.


Global Area Network (GAN)
Main article: Global Area Network

Global area networks (GAN) specifications are in development by several groups, and there is no common definition. In general, however, a GAN is a model 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 local area networks (WLAN) [4]. INMARSAT has defined a satellite-based Broadband Global Area Network (BGAN).

IEEE mobility efforts focus on the data link layer and make assumptions about the media. Mobile IP is a network layer technique, developed by the IETF, which is independent of the media type and can run over different media while still keeping the connection.


Internetwork
Main article: Internetwork

Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:
Intranet
Extranet
"The" Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.



Intranet
Main article: Intranet

An intranet is a set of interconnected networks, using the Internet Protocol and uses IP-based tools such as web browsers, that is under the control of a single administrative entity. That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise.


Extranet
Main article: Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g. a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.


Internet
Main article: Internet

A specific internetwork , consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.

Participants in the Internet, or their service providers, use IP Addresses obtained from address registries that control assignments. Service providers and large enterprises also exchange information on the reachability of their address ranges through the BGP Border Gateway Protocol.

PHP String

Strings in PHP

String variables are used for values that contains character strings.

In this tutorial we are going to look at some of the most common functions and operators used to manipulate strings in PHP.

After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.

Below, the PHP script assigns the string "Hello World" to a string variable called $txt



The Concatenation Operator

There is only one string operator in PHP.

The concatenation operator (.) is used to put two string values together.

To concatenate two variables together, use the dot (.) operator:



If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string.

Between the two string variables we added a string with a single character, an empty space, to separate the two variables.

PHP Variables

Variables in PHP

Variables are used for storing a values, like text strings, numbers or arrays.

When a variable is set it can be used over and over again in your script

All variables in PHP start with a $ sign symbol.

The correct way of setting a variable in PHP:$var_name = value;


New PHP programmers often forget the $ sign at the beginning of the variable. In that case it will not work.

PHP is a Loosely Typed Language

In PHP a variable does not need to be declared before being set.

In the example above, you see that you do not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on how they are set.

In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.

In PHP the variable is declared automatically when you use it.


Variable Naming Rules
A variable name must start with a letter or an underscore "_"
A variable name can only contain alpha-numeric characters and underscores (a-Z, 0-9, and _ )
A variable name should not contain spaces. If a variable name is more than one word, it should be separated with underscore ($my_string), or with capitalization ($myString)

PHP Syntax

You cannot view the PHP source code by selecting "View source" in the browser - you will only see the output from the PHP file, which is plain HTML. This is because the scripts are executed on the server before the result is sent back to the browser.


Basic PHP Syntax

A PHP scripting block always starts with . A PHP scripting block can be placed anywhere in the document.

On servers with shorthand support enabled you can start a scripting block with .

However, for maximum compatibility, we recommend that you use the standard form (?>


A PHP file normally contains HTML tags, just like an HTML file, and some PHP scripting code.

What Are Software Engineering Metrics?

Metrics are units of measurement. The term "metrics" is also frequently used to mean a set of specific measurements taken on a particular item or process. Software engineering metrics are units of measurement that are used to characterize:

software engineering products, e.g., designs, source code, and test cases,

software engineering processes, e.g., the activities of analysis, designing, and coding, and

software engineering people, e.g., the efficiency of an individual tester, or the productivity of an individual designer.

If used properly, software engineering metrics can allow us to:

quantitatively define success and failure, and/or the degree of success or failure, for a product, a process, or a person,

identify and quantify improvement, lack of improvement, or degradation in our products, processes, and people,

make meaningful and useful managerial and technical decisions,

identify trends, and

make quantified and meaningful estimates.

Over the years, I have noticed some common trends among software engineering metrics. Here are some observations:

A single software engineering metric in isolation is seldom useful. However, for a particular process, product, or person, 3 to 5 well-chosen metrics seems to be a practical upper limit, i.e., additional metrics (above 5) do not usually provide a significant return on investment.

Although multiple metrics must be gathered, the most useful set of metrics for a given person, process, or product may not be known ahead of time. This implies that, when we first begin to study some aspect of software engineering, or a specific software project, we will probably have to use a large (e.g., 20 to 30, or more) number of different metrics. Later, analysis should point out the most useful metrics.

Metrics are almost always interrelated. Specifically, attempts to influence one metric usually have an impact on other metrics for the same person, process, or product.

To be useful, metrics must be gathered systematically and regularly -- preferably in an automated manner.

Metrics must be correlated with reality. This correlation must take place before meaningful decisions, based on the metrics, can be made.

Faulty analysis (statistical or otherwise) of metrics can render metrics useless, or even harmful.

To make meaningful metrics-based comparisons, both the similarities and dissimilarities of the people, processes, or products being compared must be known.

Those gathering metrics must be aware of the items that may influence the metrics they are gathering. For example, there are the "terrible H's," i.e., the Heisenberg effect and the Hawthorne effect.

Metrics can be harmful. More properly, metrics can be misused.

Object-oriented software engineering metrics are units of measurement that are used to characterize:

object-oriented software engineering products, e.g., designs, source code, and test cases,

object-oriented software engineering processes, e.g., the activities of analysis, designing, and coding, and

object-oriented software engineering people, e.g., the efficiency of an individual tester, or the productivity of an individual designer.