Proxy Servers and Proxy Lists

On the Internet, proxy servers provide a way to visit sites anonymously. Proxy servers also provide network firewall, connection sharing, and caching technology for private networks.ome home networks, corporate intranets, and Internet Service Providers (ISPs) use proxy servers (also known as proxies). Proxy servers act as a "middleman" or broker between the two ends of a client/server network connection. Proxy servers work with Web browsers and servers, or other applications, by supporting underlying network protocols like HTTP.
Key Features of Proxy Servers
Proxy servers provide three main functions:

1. firewalling and filtering
2. connection sharing
3. caching

The features of proxy servers are especially important on larger networks like corporate intranets and ISP networks. The more users on a LAN and the more critical the need for data privacy, the greater the need for proxy server functionality.
Proxy Servers, Firewalling and Filtering

Proxy servers work at the Application layer, layer 7 of the OSI model. They aren't as popular as ordinary firewalls that work at lower layers and support application-independent filtering. Proxy servers are also more difficult to install and maintain than firewalls, as proxy functionality for each application protocol like HTTP, SMTP, or SOCKS must be configured individually. However, a properly configured proxy server improves network security and performance. Proxies have capability that ordinary firewalls simply cannot provide.

Some network administrators deploy both firewalls and proxy servers to work in tandem. To do this, they install both firewall and proxy server software on a server gateway.

Because they function at the OSI Application layer, the filtering capability of proxy servers is relatively intelligent compared to that of ordinary routers. For example, proxy Web servers can check the URL of outgoing requests for Web pages by inspecting HTTP GET and POST messages. Using this feature, network administrators can bar access to illegal domains but allow access to other sites. Ordinary firewalls, in contrast, cannot see Web domain names inside those messages. Likewise for incoming data traffic, ordinary routers can filter by port number or network address, but proxy servers can also filter based on application content inside the messages.
Connection Sharing with Proxy Servers
Various software products for connection sharing on small home networks have appeared in recent years. In medium- and large-sized networks, however, actual proxy servers offer a more scalable and cost-effective alternative for shared Internet access. Rather than give each client computer a direct Internet connection, all internal connections can be funneled through one or more proxies that in turn connect to the outside.
Proxy Servers and Caching
The caching of Web pages by proxy servers can improve a network's "quality of service" in three ways. First, caching may conserve bandwidth on the network, increasing scalability. Next, caching can improve response time experienced by clients. With an HTTP proxy cache, for example, Web pages can load more quickly into the browser. Finally, proxy server caches increase availability. Web pages or other files in the cache remain accessible even if the original source or an intermediate network link goes offline.

Computer Network Speed

Bandwidth in computer networking refers to the data rate supported by a network connection or interface. Network bandwidth is not the only factor that contributes to the perceived speed of a network. A lesser known but other key element of network performance - latency - also plays an important role.

What Is Network Bandwidth?

Bandwidth is the primary measure of computer network speed. Virtually everyone knows the bandwidth rating of their modem or their Internet service that is prominently advertised on network products sold today.

In networking, bandwidth represents the overall capacity of the connection. The greater the capacity, the more likely that better performance will result. Bandwidth is the amount of data that passes through a network connection over time as measured in bps.

Bandwidth can refer to both actual and theoretical throughput, and it is important to distinguish between the two. For example, a standard dialup modem supports 56 Kbps of peak bandwidth, but due to physical limitations of telephone lines and other factors, a dialup connection cannot support more than 53 Kbps of bandwidth (about 10% less than maximum) in practice. Likewise a traditional Ethernet network theoretically supports 100 Mbps of bandwidth, but this maximum amount cannot reasonably be achieved due to overhead in the computer hardware and operating systems.

Broadband and Other High Bandwidth Connections

The term high bandwidth is sometimes used to distinguish faster broadband Internet connections from traditional dialup or cellular network speeds. Definitions vary, but high bandwidth connections generally support data rates of minimum 64 Kbps (and usually 300 Kbps or higher). Broadband is just one type of high bandwidth network communication method.

P2P

Definition: The term P2P refers to "peer-to-peer" networking. A peer-to-peer network allows computer hardware and software to function without the need for special server devices. P2P is an alternative to client-server network design.

P2P is a popular technology for file sharing software applications like Kazaa, WinMX and Overnet. P2P technology helps the P2P client applications upload and download files over the P2P network services.

P2P technology can also be found in other places. Microsoft Windows XP (starting with Service Pack 1), for example, contains a component called "Windows Peer-to-Peer Networking." P2P is especially popular in homes where an expensive, decidated server computer is neither necessary nor practical.

Finally, the P2P acronym has acquired a non-technical meaning as well. Some people have described this second meaning of "P2P" as "people-to-people." From this perspective, P2P is a model for developing software and growing businesses that help individuals on the Internet meet each other and share common interests. So-called social networking technology is an example of this concept.

VPN

A VPN supplies network connectivity over a possibly long physical distance. In this respect, a VPN is a form of Wide Area Network (WAN). VPNs enable file sharing, video conferencing and similar network services. Virtual private networks generally don't provide any new functionality that isn't already offered through alternative mechanisms, but a VPN implements those services more efficiently / cheaply in most cases.

A key feature of a VPN is its ability to work over both private networks as well as public networks like the Internet. Using a method called tunneling, a VPN use the same hardware infrastructure as existing Internet or intranet links. VPN technologies includes various security mechanisms to protect the virtual, private connections.

Specifically, a VPN supports at least three different modes of use:

* Internet remote access client connections
* LAN-to-LAN internetworking
* Controlled access within an intranet

Internet VPNs for Remote Access
In recent years, many organizations have increased the mobility of their workers by allowing more employees to telecommute. Employees also continue to travel and face a growing need to stay connected to their company networks.

A VPN can be set up to support remote, protected access to the corporate home offices over the Internet. An Internet VPN solution uses a client/server design works as follows:

1. A remote host (client) wanting to log into the company network first connects to any public Internet Service Provider (ISP).

2. Next, the host initiates a VPN connection to the company VPN server. This connection is made via a VPN client installed on the remote host.

3. Once the connection has been established, the remote client can communicate with the internal company systems over the Internet just as if it were a local host.

Before VPNs, remote workers accessed company networks over private leased lines or through dialup remote access servers. While VPN clients and servers careful require installation of hardware and software, an Internet VPN is a superior solution in many situations.
VPNs for Internetworking
Besides using virtual private networks for remote access, a VPN can also bridge two networks together. In this mode of operation, an entire remote network (rather than just a single remote client) can join to a different company network to form an extended intranet. This solution uses a VPN server to VPN server connection.
Intranet / Local Network VPNs
Internal networks may also utilize VPN technology to implement controlled access to individual subnets within a private network. In this mode of operation, VPN clients connect to a VPN server that acts as the network gateway.

This type of VPN use does not involve an Internet Service Provider (ISP) or public network cabling. However, it allows the security benefits of VPN to be deployed inside an organization. This approach has become especially popular as a way for businesses to protect their WiFi local networks.

Internet Connection Alternatives for Home Networks

As a homeowner (or renter), you likely have several options for how to connect to the Internet. The connection method you choose affects how a home network must be set up to support Internet connection sharing. Each Internet network connection alternative is described here.
DSL - Digital Subscriber Line
DSL is one of the most prevalent forms of Internet connection. DSL provides high-speed networking over ordinary phone lines using digital modems. DSL connection sharing can be easily achieved with either wired or wireless broadband routers.

In some countries, DSL service is also known as ADSL, ADSL2 or ADSL2+. More About DSL
Cable - Cable Modem Internet
Like DSL, cable modem is a form of broadband Internet connection. Cable Internet uses neighborhood cable television conduits rather than telephone lines, but the same broadband routers that share DSL Internet connections also work with cable.

Cable Internet is perennially more popular than DSL in the United States, but in many other countries the reverse is true. More About Cable Modem
Dial Up Internet
Once the world standard for Internet network connections, dial up is slowly being replaced with higher-speed options. Dial up uses ordinary telephone lines but, unlike DSL, dial up connections take over the wire, preventing simultaneous voice calls.

Most home networks employ Internet Connection Sharing (ICS) solutions with dial up Internet. Dial up routers are difficult to find, expensive, and generally do not perform well given such a slow Internet pipe.

Dial up is most commonly utilized in lightly populated areas where cable and DSL Internet services are unavailable. Travelers and those with unreliable primary Internet services also use dialup as a solid secondary access method. More About Dial Up
ISDN - Integrated Services Digital Network
In the 1990s, ISDN Internet served many customers wanting DSL-like service before DSL became widely available. ISDN works over telephone lines and like DSL, supports simultaneous voice and data traffic. Additionally, ISDN provides 2 to 3 times the performance of most dial up connections. Home networking with ISDN works similarly to networking with dial up.

Due to its relatively high cost and low performance compared to DSL, today ISDN is only a practical solution for those looking to squeeze extra performance from their phone lines where DSL is unavailable. More About ISDN
Satellite Internet
Enterprises like Starband, Direcway and Wildblue offer satellite Internet service. With an exterior-mounted mini-dish and a proprietary digital modem inside the home, Internet connections can be established over a satellite link similar to satellite television services.

Satellite Internet can be particularly troublesome to network. Satellite modems may not work with broadband routers, and some online services like VPN and online games may not function over satellite connections.

Subscribers to satellite Internet service generally want the highest available bandwidth in environments where cable and DSL are unavailable. More About Satellite Internet
BPL - Broadband over Power Line
BPL supports Internet connections over residential power lines. The technology behind power line BPL works analogously to phone line DSL, using unused signaling space on the wire to transmit the Internet traffic. However, BPL is a controversial Internet connection method. BPL signals generate significant interference in the vicinity of power lines, affecting other licensed radio transmissions. BPL requires specialized (but not expensive) equipment to join to a home network.

Do not confuse BPL with so-called powerline home networking. Powerline networking establishes a local computer network within the home but does not reach to the Internet. BPL on the other hand, reaches to the Internet Service Provider over utility power lines.

(Likewise, so-called phoneline home networking maintains a local home network over phone lines, but does not extend to the Internet connection of a DSL, ISDN or dial up service.) More About BPL
Other Forms of Internet Connectivity
In fact, several other types of Internet connections have not yet been mentioned. Below is a short summary of the last remaining options:

* Fractional T1/T3 Internet - T1 and T3 are the names telecommunications firms have given to leased line network cables. Installed in some multi-resident dwellings, fractional T1/T3 lines are typically underground fiber or copper cables that connect directly to the service provider, with individual home connections switched over Ethernet cables.

* Cellular Internet - Mobile Internet connections can be made over digital cell phones. Due to high cost, cellular Internet will only be used in homes during emergencies.

* Wireless Broadband Internet - WiMax technology supports high-speed wireless Internet via base stations like cellular networks. So-called WiFi community or "mesh" networks serve a similar function using different technologies.

Device gives parents their child's eye view

Jessi is watching her 5-year-old son John playing at a nursery in public school, Australia. She works full-time, and wonders how John gets on when they are apart. In this way, she's like many other mothers. Yet for the next five weeks, ITHERIA will gain insights into her child's life that few parents have before.

She and John are taking part in an experiment to test a unique child safety device. The technology builds on existing devices that can track the location of a child, but this gadget also monitors what the child is seeing, and even their pulse. If a child's heart rate is faster than usual, it snaps a photo of their point-of-view and alerts parents via email.

The device's makers, a team led by Amrita Lee at the University of CQU, say carers could use it to identify bullying, for instance. It could also reveal if a child is separated from other device-wearing children for a given stretch of time. A password-protected website allows parents to access an activity log and photos taken during the day.

During the trial, 10 children aged 2 to 6 will wear the 97-gram device for several hours a week. As well as a camera, it holds an accelerometer with gyroscope, a GPS receiver and a digital compass. The heart rate monitor sits under clothing.
Light play

When New Scientist visited, the children were showing off their colourful devices to each other. "The devices have been sturdy and have endured kids falling off of play equipment and accidentally hitting them," says Lee. "It was important for us to make sure these were light and children's activities wouldn't be hindered by the device, and it was equally important they would want to wear it."

To minimize possible effects from exposure to electromagnetic waves, the units are set to emit signals that are only a hundredth of what an average cellphone emits. "The signals are weak, but we set it up that way to make it safe," says team-member Masatoshi Hamanaka. The weak signals mean that 30 relay points and 18 transmitters needed to be planted around the nursery.

Right now, each device costs roughly 100,000 yen (£800) to make. But with cheaper sensors, the team aims to manufacture the devices for half that price. Lee also sees the device being used in the care of people with dementia.
Privacy concern

Future experiments are planned for school children aged 6 to 11 in Japan, with an additional microphone that can pick up and store the wearer's conversations.

Kenji Kiyonaga, who researches child safety at Japan Women's University in Tama, Kawasaki, says the technology is intrusive, but would be tolerated in Australia, at least in the near future. "Standards of privacy are low here," he says. "In the US or Europe, there would be much more controversy surrounding such child-tracking devices." Even if it's lightweight, the strap would feel oppressive for the child, he adds.

Lee brushes off such criticism. "I'm a mother and I'd say that if it's a parent's choice between a child's privacy and keeping them safe, most would choose the latter," she says. The strap has been carefully designed to be comfortable, she adds.

Network Technical Requirement

Network Protocols
Protocols are the rules by which network operate. They set the standards for error detection, control sequence, message lengths, media access and so on. All networks must use a protocol and, in general, the protocol must be common to all nodes on the network. The following paragraphs offer a quick review of three of the major protocols in use today, NetBEUI, IPX/SPX and TCP/IP.

NETBEUI
NEtBEUI (NetBIOS extended user interface) is an enhanced version of the NetBIOS(network basic input/output system) protocol and was developed when computer networking primarily meant local area networking for a relatively small number of computers,from two computers to about 200. It was not developed to take into account enterprise networks where frames are directed from one network to another through routing and routers. For this reason, NetBEUI is well suited for small local area networks(LANs).

IPX/SPX
IPX/SPX (Internet packet exchange/sequenced packet exchange) is the protocol stack (several layers of software that define the protocol)used primarily by Novell Netware. One advantage it has over NetBEUI is that it has routing capabilities, so data can be transported over multiple networks. A companion protocol is SPX which enables the exchange of application specific data with greater reliability than IPX.
TCP/IP
TCP/IP (transmission control protocol/Internet protocol) is a protocol stack and is the communications protocol used on the Internet. If your LAN will be connected to the Internet you will need to enable TCP/IP protocol. Before setting up TCP/IP, you will need to make a decision about how to set up IP addressing on the network. The options are to use either static addressing or dynamic addressing.. Static addressing involves assigning a unique IP address to each workstation permanently. Dynamisc addressing automatically assigns an IP address to s computer each time it is logged on: this method is called dynamic host configuration protocol (DHCP).TCP/IP is well suited to medium to large networks. It is designed for routing, is highly reliable and offers better security than NetBEUI. The size of the protocol suite is large and hence its implementation on MS-DOS machines is difficult, especially the older ones. The other disadvantage is the slow speed of the protocol because of high implementation overheads.

Network hardware
When we refer to network hardware we are talking about a range of electronic devices that can be interconnected in such a way as to allow the transmission of communication signals between a number of workstations. These devices range from simple generic hubs to sophisticated proprietary hardware such as routers and gateways. To help gain a better understanding of how these devices interact with each other you need a knowledge of what devices are available and how they work.
The following represents some of the more commonly used network hardware components.
Network interface cards
Network interface cards(NICs) are the most common type of network hardware on a network. Every workstation and server will contain at least one NIC. NICs contain the electronic components that establish and control network communications. The NIC is the principle hardware device that differentiates between a networked computer and a stand –alone computer.
Transmission media
The transmission media or cables are the most important component of a network; after all, it is the cables that provide the physical connections between the workstations and that server. There are several different types of cable that can be used in networking and, although many networksuse a particular cable type exclusively, increasingly more and more networks are using a combination of different cable types. The choice of cable for your network needs to be considered carefully, as different cable s not only transmit at different speeds but also have different distance limitations. The two most common cable types used in modern networks are coaxial cable and twisted pair.
Hubs
Hubs are one of the most basic pieces of networking equipment available. Physically a hub is a box with a number of RJ45 ports(typically between 4 and 32) that allows you to connect several networking devices together using twisted pair (CAT 5) network cables.

Routers, switches and bridges

Switches look nearly identical to hubs, but a switch generally contains more intelligence than a hub. Unlike hubs,network switches are cable of inspecting the data packets as they are received, determining the source and destination device of tht packet, and forwarding that packet appropriately. By delivering messages only to connected device that it was intended for,network switches concerve network band width and offer generally better performance than hubs. Most switches are active: that is, they electrically amplify the signal as it moves from one device to another.
Bridges are devices that allow you to segment a large network into two smaller, more efficient networks. If you are adding to an older wiring scheme and want the new network to be up-to- date, a bridge can connect the two.
Routers translate information from one network to another; it is similar toa bridge with extra intelligence. Routers select the best path to route a message, based on the destination address and origin. The router can direct traffic to prevent head-on collisions, and is smart enough to know when to direct traffic along back roads and shortcuts.

Microsoft to open online PC game store

Microsoft plans to open a new online PC game store called Games for Windows Marketplace in the middle of November, it said Monday.

Microsoft will ready over 100 titles from various game makers for the launch, including many of the biggest hits from Microsoft Game Studios, including "Fable: The Lost Chapters," "Flight Simulator," "Gears of War," "Halo" and "Age of Empires Online." Other big titles in stock include "Grand Theft Auto III," and "Max Payne" from Rockstar Games and "Deus Ex: Game of the Year Edition" from Square Enix. The site will also host indie game titles, Microsoft said.

PC game lovers will be able to access the store at any time to buy games or to download them again if necessary, Microsoft said. Special deals will be used to lure gamers to the site, such as weekly and seasonal deals.

"The Games for Windows Marketplace will offer PC gamers a robust lineup of games they love, easier navigation and purchase, and recurring specials such as Deal of the Week," Microsoft said.

It will launch Nov. 15 at www.gamesforwindows.com.

Anyone with a Windows Live ID, including Windows Live, Xbox Live, Games for Windows -- Live or Zune account, can login to the new Games for Windows Marketplace. Microsoft Points can also be used at the store.

Information System in Organisation

The business problem

Information technology plays an important part in any organisation.Information technology
provides information systems that help people within the organisation do their particular tasks.
User requirements and technology are constantly changing. New or updated systems need to be introduced.
When any service is to be provided, the needs of the client should be determined before that service is provided.
If you do not know what the client requires,how can you be sure the client's needs are being satisfied?
In this unit you will look at how to determine client requirements.Different techniques to help you will be discussed.


Organisations and Information Systems

An organisation is a group of people all working towards a comman goal.This is a very general description that covers
a great numbers of groups.Indeed, it is difficult to think of any group of people that is not an
organisation.one example is a group of people who are competing in some way,such as a group of athlets in a race.That group
of athletes in a race. That group of athletes is not an organisation.Working towards a comman goal,or number of goals,is an important
goal,or number of goals,is an important characteristic of an organisation.
Organisations can be characterised by:
size, Industry and ownership.
Organisations range in size from one person to many thousands of people.We often use the terms 'small' and 'large' organisation.This
distinction is quite arbitary. Some say an organisation of up fifty people is small, others say a hundred.

Industry
Organisations can be categorised by the type of industry they are involved with. usually, there are many organisations within an industry.
Ownership
Organisations can be categorised by their ownership of the organisation may be private,government or social.
Individuals own organisations in the private sector.
Information Systems:
Every type of organisation has requirement for information system.An information system can be describe as a set of resources that work together
to process data into meaningful information that the organisation can in its business.
Resources are numerous,including people.Information technology resources include computer hardware
9for e.g cpu,monitor,keyboard),communication infrastructure(for exmple networks) and software.Information technologyis very technology is
veryintegrated allowing people to exhange information within an organisation( for example,by an internet) for externally
(for example,images,graphs)or non graphical.

Information systems are an important part of an organisation. Now we will consider the people
who use these information systems. These people are known as users. Users may interact
with the system directly,for example,by entering data or reading information on a screen users
Users may interact with the system directly, for example,by entering dat on reading information
on a screen users may also interact indirectly by reciving a computer generated reports.
There are various types of users. They include:
Operational staff
managers
customers
shareholders
general public

Operational staff: The operational staff are the workers. They actually use the information system
to help them do their business.
Managers: Middle managers, or line managers, manage the operational part of the business.They
supervise staff and the operations,make decision and provide leadership at the level.
Information systems help them perform those tasks.
Customers:
Customers do not work for the organisation,but do have interaction with the organisation's
computer systems.They can be indirect users,such as a person who receives an invoice from
a computerised invoicing system.The advent of the internet and e-commerce system has greatly
increased the direct interaction of users with organisation's computer systems. Customers are an
important consideration in determining information system requirements.

Shareholders
Shareholders are owners of organisations but do not take part in the day-to- day running of the organisation.By purchasing in
the organisation. By purchasing shares in the organisation,shareholders receive part of the profits. They also gain the right to
elect members to the board.They become indirect users of the organisation's information systems.The organisation must fully inform the sharehold-
ers of its performance.
Information Systems are very important in providing accurate and relevant information to shareholders. The legal
consequences of incorrect reporting to shareholders can be quite severe.
General public:
Increasingly, the general public is being exposed to information systems.This is particularly
the case with computerised information system. People actually use organisations' information
systems.There is no better example of this than the Internet.Many organisations are providing
information about their services on the Internet.Many organisations are providing information
about their services on the Internet.

Information System s provided by computers are a very important of an organisations need effective
computer systems to do their business and cannot survive witout them.Users interact with information
systems in different ways-for example ,operational staff and customers interact in order to do business
and customers interact in order to do business, and managers interact to make decisions.
Information systems can be quite complex.care must be taken in determining what users want from information systems. Techniques such as interviewing
and questionnaries are used to collect information requirements, which are then documented
and presented to the client for approval.

Technical Documentation

Internet/Intranet
The Internet has become a rich source of information, including computing
systems documentation. Information about all types of hardware and
software can be found. Some information comes from the suppliers,
although much of it is from other parties.
Documentation is often found on an organisation’s intranet. For example,
the Intel website (www.intel.com) provides technical specifications of hardware
components.
Help files
Help files are common in many applications, reflecting the increasing
popularity of online documentation. Help files often provide detailed and
structured information so that the user can find what they want without the
inconvenience of a bulky manual.
Help files can now be produced in HTML format using Microsoft’s HTML
Help. These help files can be viewed by Internet browsers such as Internet
Explorer and Netscape.
Multimedia
Text, graphics, video, animation, sound and interactivity can be integrated
into online documentation – this is known as multimedia documentation
because it uses a range of communication media. Information can also be
organised as a database – this allows selected information to be retrieved
quickly and accurately, making online media dynamic and powerful.
CD/DVD
Large volumes of information can be stored on CD or DVD. This is now the
cheapest and most flexible way of providing documentation.

The purpose of technical documentation is to provide information for people
who build and maintain computer systems. Computer engineers and
technicians, network engineers and administrators, systems analysts, system
designers, data analysts, programmers, technical/manual writers
(documentation specialists) and software testers need to know how a system
works, although different people are interested in different aspects of
the system. Figure 1.3 shows a computer technician referring to some documentation
while fixing a computer.
A data analyst in charge of a corporate
database might only be interested in
knowing about the data used by the
system. Clearly there should be a
description of the data used – in this
case, in a data dictionary. A programmer,
on the other hand, is more
interested in the logic of a program – if
a program is malfunctioning. In this
case the information will be found in a
program specification, which may be
textual, diagrammatic or both. A user
manual such as a training document
requires information such as screen
and report layouts, which are provided
in the technical documentation. For
example, a writer may want to develop a sales brochure, and so refers to the
technical documentation for information about the product. A software tester
may need samples of typical data to be used with the application in order to test
the software effectively. A network engineer may need technical documentation
to set up a network.
Other people who may need to refer to the documentation include project
managers, system managers and computer operations staff.
Methodologies for producing documentation
A methodology describes the approach and the steps used in a particular discipline.
For example, accountants have methodologies for preparing
financial reports, software developers have methodologies to prepare software,
and technical writers have methodologies for preparing
documentation.
A widely accepted methodology for developing computer system documentation
is the standard documentation process. The starting point in this
process is the document library blueprint – this is a description of the
different types of documentation required (such as training manual,
procedure manual, online help). It is a specification of the documentation
to be produced.
The document library blueprint is used to obtain user acceptance and project
management approval for the form, style and purpose of the
documentation. It also serves as a planning aid in development.
Individual document blueprints are specified after the document library
blueprint has been approved. These individual specifications are more than
an outline. They identify the context of the document, its purpose and the
detailed content. Figure 1.4 shows the stages and their sequence in the
standard documentation process.
The development of the documentation is a project in itself, and so good
project management methods are needed. The development of computer
system documentation has its own life cycle. As shown in figure 1.4, the
stages that make up the development process are:
planning
drafting
reviewing
testing
producing
distributing
updating.
Planning
As in other disciplines such as constructing a building or developing software,
planning is essential. Just as a builder
would not start building a house without a
schedule, specification and budget, you should
not start writing the documentation without planning first. As part of the
planning process, you need to:
create a document library blueprint
determine the resources required
develop a schedule
determine the budget.

Creating a document library blueprint
Creating the document library blueprint involves identifying all the pieces of
documentation and how they are related, and developing a specification for
each – known as the document specification. The document library blueprint
and specifications provide the information the authors need to produce the
documentation.
The individual document specification covers the document’s:
purpose
audience
— characteristics
— needs
— diversity
related documents
media
production plan
reviewing and testing
update plan.
These should be specified to a level of detail that will enable a documentation
developer to produce the documentation. They should be sufficiently
clear and detailed for another person to use them.
Purpose
The purpose of the document is to define the reason why this documentation
is produced. This may be addressed in the form of objectives for the documentation.
The following are some examples of technical documentation
objectives:
to enable a person to assemble a computer
to enable a software engineer to change software
to help a database administrator to manage a database
to assist a computer technician to repair a computer.
Intended reader
The intended reader or user must be identified. Their background and any
other relevant factors related to their use of the computer system must be
stated. Factors such as language, culture, attitudes and environment may be
important. The characteristics of the reader are often described in the final
documentation. Figure 1.5 shows a description of the reader given in the
introduction of the banking ma

Hub, Router and Switch

A hub is typically the least expensive, least intelligent, and least complicated of the three. Its job is very simple: anything that comes in one port is sent out to the others. That's it. Every computer connected to the hub "sees" everything that every other computer on the hub sees. The hub itself is blissfully ignorant of the data being transmitted. For years, simple hubs have been quick and easy ways to connect computers in small networks.

A switch does essentially what a hub does but more efficiently. By paying attention to the traffic that comes across it, it can "learn" where particular addresses are. For example, if it sees traffic from machine A coming in on port 2, it now knows that machine A is connected to that port and that traffic to machine A needs to only be sent to that port and not any of the others. The net result of using a switch over a hub is that most of the network traffic only goes where it needs to rather than to every port. On busy networks this can make the network significantly faster.

A router is the smartest and most complicated of the bunch. Routers come in all shapes and sizes from the small four-port broadband routers that are very popular right now to the large industrial strength devices that drive the internet itself. A simple way to think of a router is as a computer that can be programmed to understand, possibly manipulate, and route the data its being asked to handle. For example, broadband routers include the ability to "hide" computers behind a type of firewall which involves slightly modifying the packets of network traffic as they traverse the device. All routers include some kind of user interface for configuring how the router will treat traffic. The really large routers include the equivalent of a full-blown programming language to describe how they should operate as well as the ability to communicate with other routers to describe or determine the best way to get network traffic from point A to point B.

In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.

Topology in Network Design

Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

Network topologies are categorized into the following basic types:

• bus
• ring
• star
• tree
• mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Illustration - Bus Topology Diagram

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Star Topology

Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Summary

Topologies remain an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.