Types of networks:

LAN (Local Area Network):

It is a set of computers and devices connected together. Each device is called a node: (computer, printer etc)

A LAN is confined to one site. It covers a small geographical area of under a mile. Examples: homes, buildings, schools, hospitals.

The network owner owns the network’s infrastructure, for example, cables.

Why use a LAN?

• Sharing files is easier – network users can access the same files. This also work collaborating and to copy files between machines.

• Can share the same hardware, for example: printers,

• Internet connection can be shared between every device connected on a LAN

• The installation and updating of software can be done centrally rather than one each computer one by one.

• Communication between users in a LAN is cheaper and easier.

• User accounts can be stored centrally on a server; this means that users can log in from any device on the network.

WAN (Wide Area Network)

A WAN connect LANs that are in different geographical locations. For example, a business with offices in different countries would need a WAN for all their devices to connect together.

This covers a large geographical area of over a mile. For example, the internet as it is a massive network of connected networks.

The network infrastructure, for example cables, are owned by other telecommunications organisations. This means that a WAN is more expensive to set up than a LAN.

Factors that affect the performance of networks:

• Bandwidth is the amount of data that can be transferred in a given time. The greater the bandwidth, the better the network can perform. It is shared between all active users on the network. This means that if they are many users active, or if there is heavy use on the network (streaming video), this can slow down the network.

• Wired connections are generally much faster and more reliable than wireless. The type of wires used can affect the performance of the network. For example: Fibre-optic can give much better performance then Ethernet.

• Choice of hardware (NICs, switch and routers) and the network topology can have an effect on the performance on the network.

Client-Server Model: (One of the most common modern networking model)

The Client: Sends requests to the server

The Server: The server will process the request and send a response. Can also provide services such as; storing files, printing, hosting a website

A client server is centralized since clients communicate with a central server.

Advantages of client servers:	Disadvantages of client servers:
Easier to keep track of files as they are stored centrally	Expensive to set up and needs IT specialists to maintain the network and server
Easier to perform back ups	Server dependence – if the server goes down all clients lose access to their work
Easier to install and update software	The server can become overloaded if too many clients are accessing it at once.
Easier to manage network security
Servers are very reliable and are always on

(Doesn’t say on the specification that we must know the advantages and disadvantages of a client server but the text book, and Pixel is mentioning it. Never know what OCR will ask)

Peer-To-Peer Networks

• Every device on the network is known as a ‘Peer’. Each peer can act as both client and server depending on what task is trying to be accomplished.
• Each peer on the network is responsible their own maintenance and making sure that they remain connected to the network

Uses of Peer-To-Peer Networks:

• File transfer
• Streaming video (could be from your computer to your phone)
• Wireless printing
• Bluetooth speakers

Advantages of Peer-to-Peer Networks:	Disadvantages of Peer-to-Peer Networks:
Easy to maintain – Don’t need any expertise or expensive hardware.	No centralized management – devices need their updates and security installed individually. This makes backups complicated.
No dependence on server – if one device fails, the whole network isn’t lost	Copying files between devices create duplicate files. This means that it is easy to lose track of what’s stored where and which files are up to date.
	Peer machines are less reliable and data may be lost if one fails
	Machines can slow down when other devices access them

Hardware used in a Local Area Network:

• A Network interface controller (NIC): This is an internal piece of hardware in a device that allows it to connect to a network.
• Switch – This used to connect devices on a LAN. Switches receive data from one device and transmits the data to the device on the network with the correct MAC address.
• Routers – Responsible for transmitting data between networks. Routers direct data (packets) to their destination. Used in homes and offices to connect a LAN to the internet.
• Transmission Media: These are the cables.

Transmission media:

1. Ethernet cables – These are used to connect devices in a LAN. They are twisted copper cables. They are twisted together to help reduce internal interference.
2. Coaxial cables. There are made from a single copper wire surrounded by a plastic layer for insulation and metallic mesh which provides shielding from outside interference. (I have been told that we won’t be asked about these by my teacher, however I know about them, the text book is mentioning it and so is Seneca. No harm in not knowing)
3. Fibre optic cables – These transmit data as light. They have extremely high performance and do not suffer from interference and can transmit data over very large distances without loss of signal quality. However, they are expensive.

Domain Name System: (DNS) 

Exam Note: Some of you know this as ‘Domain Name Server’ However, after looking from OCR’s end of unit four quiz, they accept the answer as ‘Domain Name System’ – Lets just be safe and say its ‘system’.

• This is the system used to find the computer which hosts the website you are looking for.
• When the user uses a domain name (or URL) to search for a website, the client sends a request to the DNS asking for the IP address for that domain name. The DNS will process the request and will respond with the correct IP address. The client then uses that IP address to view associated with that domain name.

Hosting:

‘Web hosting is the act of keeping a website on a server and allowing clients to request to see the pages of the website’ (Perfect definition given by Seneca)

The World wide web (WWW) is a collection of websites that are hosted on web servers and accessed through the HTTP protocol.

Setting up a web server:

This can be difficult to set up as:

• There are a lot of security risks
• It can be difficult to make sure that the server does not go down, for example if there is a power cut.
• Web servers are expensive.

Hosting provider:

A web hosting company will charge a monthly fee in return for hosting your site for you. They will:

• Host your website
• Regularly back up your site
• Apply security patches for you

The Cloud:

This is the storage, services and applications that exist on the internet rather than on local secondary storage.

The cloud is used for:

• Streaming services – can store audio and video which is then streamed by users, for example, Netflix and Spotify.
• Server hosting – can be used to host websites, for example, Amazon web services and Microsoft azure.
• File storage and sharing – can be used to store files and allow them to be shared easily, for example, google drive and dropbox.
• Applications – These can now be accessed through the cloud so there is no need to install them on secondary storage, for example, google docs.

Advantages of the cloud:	Disadvantages of the cloud:
Users can access files from any device that is connected to the internet	Need connection to the internet to access files
Easy to increase how much secondary storage is available	Dependent on host for security and back-ups
No need to buy expensive hardware to store data	Data is in the cloud can be vulnerable to hackers
No need to pay IT staff to manage the hardware	Unclear who has ownership over cloud data
Cloud host provides security and backups for you	Subscription fees for using cloud storage and software may be expensive
Cloud software will be updated automatically

Virtual Networks:

A virtual network is a software-based network that can share the same physical hardware with other virtual networks:

This allows us take advantage of:

• Remote connections – The use of virtual networks can allow people to connect remotely to a network. This lets them securely access resources on the network.
• Security – Virtual networks allow administrators to set limits on traffic and segment networks to keep the network secure.
• Hardware sharing – More than one virtual network may share the same hardware. This reduces the cost of buying hardware. This means that we only have to maintain one set of hardware.