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Architecture, Firewalls and Proxy Servers

Networks

+ Clients and Servers

Client computers, or workstations, are normal computers that people sit at to get their work done.

Servers are special, powerful computers that provide ‘services’ to the client computers on the network.

Services might include: Providing a central, common file storage area Sharing hardware such as printers Controlling who can or can’t have access to the network Sharing Internet connections

Servers are built to be reliable. This means that they are much more expensive than normal computers.

In a small network one server might provide all of these services. In a larger network there might be many servers sharing the work.

+ Network Topology Network topology means the arrangement and

connection of the network.

Types:

Bus Network – Network connected with a long, central cable, the ‘bus’ is used to connect all of the computers together. Each computer has a short cable linking it to the ‘bus’.

Ring Network – Network where each computer is connected to a loop of cable, the ‘ring’.

Star Network – Network where every computer is connected to a central device. The device passes messages between computers.

+ Thin Client A Thin Client is that which relies on a server to store

files and applications as well as to run software.

A Thin Client is a very basic computer that simply accepts input and displays output. There tend to be very low specifications in a Thin Client

An example of a Thin Client is a library computer while Google Chromebooks have begun to be marketed as Thin Client alternatives.

+ Fat Client A fat client is a networked computer with many locally-

stored programs or resources and little dependence on network resources.

A fat client is often built with expensive hardware with many advances specifications. An example of a fat client is a computer that handles the majority of a complex drawing’s editing.

A fat client has several advantages, including: Fewer server requirements because it does most of the

application processing

and More offline work because a server connection is often not

required

+ Peer-to-Peer Network A peer-to-peer network is that which all clients have a

say in the way the network is managed. This usually takes place in locations like the home since a complex network is not needed.

On such a network, all clients share files/data since all are connected to each other without a central server to monitor access.

Peer-to-peer networks can become a problem if they get too large due to their lack of management and security.

+ Firewall Firewalls can come in the form of either hardware or

software and ultimately determines what data enters and leaves the network.

In either form, a firewall prevents unauthorized users from accessing the network and/or data on the network. This is done through the use of various methods.

IP Addresses – A firewall can limit the IP addresses that have access to the network. This is done to prevent such issues as DoS Attacks or Denial of Service Attacks.

Domain Names- This method limits the sites that can be viewed by the network to minimize the risk of malicious attacks.

Protocols and Ports – This method limits web browsing, email and overall communication/transfer abilities.

+ Proxy Servers A proxy server is a computer setup to share a resource,

usually an Internet connection.

Other computers can request a web page via the proxy server. The proxy server will then get the page using its Internet connection, and pass it back to the computer who asked for it.

Proxy servers are often used instead of router since additional software can be easily installed on the computer such as anti-virus, web filtering etc.

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Types of NetworksNetworks

+Local Area Networks (LAN)

A Local Area Network is a network within one building or site.

A LAN is usually a private network belonging to an organization or business. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs.

Because LANs are geographically small, they usually use cables or low-power radio (wireless) for the connections.

+Wireless Local Area Network (WLAN) A wireless LAN (WLAN) is a LAN that uses radio signals

(WiFi) to connect computers instead of cables.

At the center of the WLAN is a wireless switch or router - a small box with one or two antennas sticking out the back - used for sending and receiving data to the computers. (Most laptops have a wireless antenna built into the case.)

It is much more convenient to use wireless connections instead of running long wires all over a building but, WLANs are more difficult to make secure since other people can also try to connect to the wireless network.

+Wide Area Networks (WAN) A Wide Area Network is that which spans over a large

area.

A WAN is often created by joining several LANs, such as when a school has different campuses that are linked together or a business has offices in different countries links the office LANs together.

Since WANs are usually geographically spread over large areas and links between computers are over long distances, they often use alternative connection technologies: (ex. optical fibre (glass) cables, satellite radio links, microwave radio links, etc.)

+Personal Area Networks Personal Area Networks are those which use short-

range connections for individual usage. This often takes place with Bluetooth technology.

The Bluetooth device uses low-power radio transmitters to connect to other devices.

Such devices are used to connect various peripheral devices such as: A wireless keyboard Wireless mouse Mobile phone

+Virtual Private Networks A virtual private network (VPN) is a network that uses

the Internet, to provide remote offices or individual users with secure access to their organization's network. These connections form a single wide-area network (WAN)

for the business.

A VPN works by using the shared public infrastructure while maintaining privacy through security procedures and tunneling protocols.

VPN software encrypts all data that is sent back and forth to ensure security. This also potentially masks the location of the client.

+Domain Names, HTTP and the Internet

Networks

+Domain Names

Domain names are essentially the website addresses that a website can be found at (ie. www.schoology.com). These domain names, or URLs (Universal Resource Locators) can be used instead of IP addresses since they are easier to remember.

A URL is broken down into several components:

Schoology.com = The domain name .com = the Top Level Domain (TLD) www.schoology.com = The host name Index.html = the file name

+Domain Name System When you type a domain name into a web browser, this is

not what the computer sees. A Domain Name System (DNS) translates domain names into IP addresses that can be read by the computer.

DNS are servers that are connected to the internet convert domain names to IPs. DNS works both ways, meaning you could put in an IP address

rather than the domain name and still gain access to a website.

DNS, or Pharming is the act of falsifying DNS data in order to direct a web user to a site they had not intended on visiting.

+HyperText Transfer Protocol (HTTP) HTTP is the protocol, or set of rules that govern

communication between web servers and browsers. This is essentially the common language that servers and browsers communicate in.

HyperText Transfer Protocol Secure, or HTTPS is an encrypted version of HTTP that offers more security to users of a website. (used when secure data is being collected or transferred.)

HTTPS uses Transport Layer Security (TLS) or Secure Socket Layer (SSL) encryption to successfully protect content.

+Synchronous or Asynchronous Transfers A Synchronous Transfer is that which takes place in

regular intervals. These types of transfers take place after the sender and receiver agree upon the content and rate at which data will be transferred. Ex. Traditional file transfer via download.

A Asynchronous Transfer is when data can be transmitted intermittently rather than in a steady stream. Essentially, data transfer can stop and start during transfer period. Ex. Skype conversation where both parties can talk

whenever they like.

+Difference between the Internet and World Wide Web

The Internet is technically a physical network of computers across the globe using TCP/IP.

The World Wide Web is a service that runs over the Internet that provides access to interlinked web pages.

The reason why the Internet and World Wide Web are different is that some aspects of the Internet, (ie. Instant messaging, P2P file sharing) use their own protocols that go beyond HTTP. Examples of this are POP3 (Post Office Protocol) and

BitTorrent Protocol.