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What is a LAN?

A local area network covers a small geographical area located on a single site.
All the hardware in a LAN is owned by the organisation that uses it.
LANs are either wired (e.g. with Ethernet cables) or wireless (using Wi-Fi).
Lots of homes have a LAN to connect various devices, such as PCs, tablets, smart TVs and printers.


What are the advantages of LAN?

Sharing files is easier - network users can access the same files, work collaboratively on them (at the same time) and copy files between machines.
You can share the same hardware (like printers) on a LAN.
The Internet connection can be shared between every device connected to the LAN.
You can install and update software on all computers at once, rather than one-by-one.
You can communicate with LAN users cheaply and easily, e.g. with instant messaging.
Users accounts can be stored centrally, so users can log in from any device on the network.


What is a WAN?

Wan stands for Wide Area Network.
A WAN connects LANs that are in different geographical locations. For example, a business with offices in three different countries would need a WAN for all their devices to connect.
Organisations hire infrastructure (e.g. communication lines) from telecommunications companies, who own and manage the WAN. This is because WAN is much more expensive to set up than WAN.
WANs may be connected using fibre optic or copper telephone lines, satellite links or radio links.
The Internet is the biggest WAN.


What factors cause the performance of networks?

Bandwidth is the amount of data that can be transferred in a given time, e.g. 500 Mbps. The greater the bandwidth, the better the network can perform.
Available bandwidth is shared between users of a network - too many users or heavy use (e.g. streaming video) may cause congestion and slow the network. You can limit the bandwidth available to individual users to address this.
Wired connections are generally faster and more reliable than wireless. Fibre optic cables can give much better performance than copper cables. Wireless performance depends on signal quality so is affected by the range of the device, the amount of interference from other devices and physical obstructions like thick walls in buildings.
Choice of hardware other than cables and network topology also have a big effect.


What is a NIC?

A Network Interface Controller is an internal piece of hardware that allows a device to connect to a network. These used to be on separate cards, but nowadays they're built into the motherboard. NICs exist both wired and wireless connections.


What are switches?

Switches connect devices on a LAN. Switches receive data (in units called frames) from one device and transmit this data to the device on the network with the correct MAC address.


What is a router?

Routers are responsible for transmitting data between networks - they're always connected to at least two different networks.
Routers have a crucial role on Internet, directing data (in units called packets) to their destination.
Routers are used in homes and offices to connect the LAN to the Internet.
Most home 'routers; are in fact a router, switch and WAP all in one.


What are ethernet cables?

Ethernet cables are used to connect devices in a LAN. The most common Ethernet cables are CAT 5e and CAT 6. They are 'twisted pair' cables, containing four pairs of copper wires which are twisted together to reduce internal interference.


What are coaxial cables?

Coaxial cables are made of a single copper wire surrounded by a plastic layer of insulation and a metallic mesh which provides shielding from outside interference.


What are fibre optic cables?

Fibre optic cables transmit light data as light. They are high performance (and therefore expensive) cables - they don't suffer interference and can transmit over very large distances without loss of signal quality.


How do wireless networks work?

Like mobile phones and TVs, wireless networks use radio waves to transmit data.
To set up a wireless network, you need a Wireless Access Point (WAP) device. The WAP is basically a switch that allows devices to connect wirelessly.
To connect, devices need wireless capability. This is usually built-in these days, but if not you can use a USB dongle. HDMI dongles are popular for TVs.


What is Wi-Fi?

Wi-Fi is the standard used for wireless networks. Wi-Fi uses two radio frequency bands - 2.4GHz and 5GHz.
The bands are split into numbered channels that each cover a small frequency range (channels overlap).
Wi-Fi performance is affected by interference between networks using adjacent channels. To avoid problems, only certain channels that are spaced apart tend to be used.


What is a client-server network?

A client-server network is managed by a server. The devices connected to the server are clients.
Files and software are usually stored centrally on the server rather than on individual client devices.
Clients send requests to the server, e.g asking for data. This is the client-server relationship.
The server stores user profiles, passwords and access information - it may request a password before fulfilling certain requests or deny requests to users without the right access level.
Most uses of the Internet work on a client-server relationship. E.g. websites are hosted on web servers. Web browsers are client programs which send requests to web servers. Web server fulfil requests (e.g by sending web pages) for thousands of clients.


What are the advantages and disadvantages of a client-server network?

Easier to keep track of files as they are store centrally.
Easier to perform back-ups.
Easier to install and update software.
Easier to manage network security (e.g. anti-malware software and user access levels).
Servers are very reliable and are always on.

Expensive to set up and needs IT specialists to maintain the network and server.
Server dependence - if the server goes down all clients loss access to their work.
The server may become overloaded if too many clients are accessing it at once.


What is a peer-to-peer network?

In a Peer-to-Peer (P2P) networks all devices are equal, connecting directly to each other without a server.
You store files on individual devices and share them with others.
You may use a P2P network at home to share files between devices, or connect devices to a printer.
Although most Internet use is client-server based, there are some common P2P applications such as video calling (like Skype) and file sharing (often used for illegal sharing of copyrighted material).


What are the advantages and disadvantages of a peer-to-peer network?

Easy to maintain - you don't need any expertise or expensive hardware.
No dependence on server - if one device fails the whole network isn't lost.

Not centralised management - devices need their updates and security installed individually. Backups are more complicated.
Copying files between devices creates duplicate files - it's easy to lost 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 are prone to slow down when other devices access them.


What are the advantages and disadvantages of a star topology?

If a devices fails or a cable is disconnected, the rest of the network is unaffected.
It's simple to add more devices to the network.
Better performance that other setups - data goes straight to the central device so all devices can transmit data at once and there are very few data collisions.

In wired networks, every device needs a cable to connect to the central switch or server. This can be expensive, e.g. for an office building with 50 terminals.
If there is a problem with the switch or server then the whole network is affected.


What is a bus topology?

In a bus topology, all devices are arranged in a line, connected to a single backbone cable. Devices send data in both directions. This causes data collisions which slows the network.


What is a ring topology?

In a ring topology, data moves in one direction around the ring preventing collisions. But only one device can send data at a time and data passes through many devices before reaching its destination.


What is a mesh topology?

A mesh topology is relative new network layout. It is decentralised - networking devices are either directly or indirectly connect to every other one without the need for one central switch or server. Mesh networks work by sending data along the fastest route from one device to another.

A full mesh topology is where every device is connected to every other device. In a partial mesh topology, not all devices are fully-connected.


What are the advantages and disadvantages of mesh topology?

No single point where the network can fail.
More practical option with wireless.

Very expensive as need lots of wires.


What is a protocol?

A protocol is a set of rules for how devices communicate and how data is transmitted across a network.

Protocols cover how communication between two devices should start and end, how the data should be organised, and what the devices should do if data goes missing.


What is a MAC address?

Every device needs a unique identifier so it can be found on a network.
MAC addresses are assigned to all network-enabled devices by the manufacturer. They are unique to the device and cannot be changed.
MAC addresses are 48 or 64-bit binary numbers. To make them easier to use they're converted into hexadecimals.
MAC addresses are mainly used by the Ethernet protocol on LANs. LAnd switches read the MAC addresses and use them to direct data to the right device.


What are IP addresses?

IP addresses are used when sending data between TCP/IP networks e.g. over the Internet.
IP addresses aren't linked to hardware, as they are assigned either manually (static) or automatically (dynamic) before the device can access the network.
An IP address can either be a 32-bit or 128-bit binary number, depending on the version of IP you're using. The longer 128-bit numbers are translated into eight hexadecimal numbers, while the 32-bit ones are converted into four denary numbers.


What are the types of IP addresses?

Static IP addresses are permanent addresses. They're used to connect printers on a LAN, and for hosting websites on the Internet - companies don't want the IP address of their website changing. Static IP addresses on the internet can be very expensive - businesses pay big money for them.

Dynamic IP addresses are assigned to the device by a network server, meaning your device may have a different IP address every time you log on to the network. Internet Service Providers (ISPs) commonly use dynamic IP addresses as they are more cost effective and can be reused.


What do packets contain?

Packet header - it contains the control information (3 bits of information).
Sequence Number - Insures that the packets are resembled in the correct order.
Return Address - Ensures sending computer is notified of the arrival or corruption of packets.
Destination Address - Where the data packet is being sent to.
Error Check - A checksum number which consists of a calculation and a answer.


What is packet switching?

Packet switching is used by routers to direct data packets on the Internet and other IP networks.

Packet switching is an efficient use of the network because there are so many possible routes that data can take - packets can reach their receiving device if there's heavy traffic.


What is TCP/IP protocol?

TCP/IP is the protocol which dictates how data is sent between networks

Transmission control protocol (TCP) sets the rules for how devices connect on the network. It's in charge of splitting the data into packets and reassembling the packets back into original data once it reaches the receiving device. It's also responsible for checking the data is correctly sent and delivered.

Internet protocol (IP) is responsible for packet switching.


What are the different types of internet based protocols?

HTTP (Hypertext Transfer Protocol) - Used by web browsers to access websites and communicate with web sources.

HTTPS (HTTP Secure) - A more secure version of HTTP. Encrypts all information sent and received.

FTP (File Transfer Protocol) - Used to access, edit and move files between devices on a network, e.g. to access files on a server from a client computer.

POP3 (Post Office Protocol version 3) - Used to retrieve emails from a server. The server holds the email until you download it, at which point it is deleted from the server.

IMAP (Internet Message Access Protocol) - Used to retrieve emails from a server. The server holds the email until you actually delete it - you only download a copy. Used by most web-based email clients.

SMTP (Simple Mail Transfer) - Used to send emails. Also used to transfer emails between servers.


What is a layer?

A layer is a group of protocols which have similar functions.
Layers are self-contained - protocols in each layer do their job without needing to know what's happening in other layers.
Each layer servers the layer above it - it does hidden work needed for an action on the layer above. E.g. when you send an email (on layer 4), this triggers actions in layer 3, which triggers actions in layer 2, all the way down to layer 1.


What are the different protocol layers?

Layer 4 (Application layer) - Turning data into websites and other applications and vice versa. E.g. HTTP, FTP, SMTP.

Layer 3 (Transport Layer) - Controlling data flow e.g. splitting data into packets and checking packets are correctly sent and delivered. E.g. TCP.

Layer 2 (Network Layer) - Making connections between networks, directly data packets and handling traffic. Used by routers. E.g. IP.

Layer 1 (Data Link Layer) - Passing data over the physical network. Responsible for how bits are sent as electrical signals over cables, wireless and other hardware. E.g. Ethernet.


What are the advantages of using layers?

It breaks network communication into manageable pieces. This helps developers concentrate on only one area of the network without having to worry about the others.
As layers are self-contained, they can be changed without the other layers being affected.
Having set rules for each layer forces companies to make compatible, universal hardware and software, so different brands will work together and always work in basically the same way.