3.5 - Fundamentals of Computer Networks (SENECA ALT)

what is a network?

a group of two or more connected devices

what do networks allow devices to do?

share information and resources

what does LAN stand for?

local area network

where does a LAN cover?

a small geographical area located on a single site.

who is the hardware for a LAN owned by?

the organisation that uses it.

how can LANs be connected

wired, or wirelessly

where will you often find LANs?

businesses, schools, homes, universities

why do homes have LANs?

to connect various devices (e.g. PCs, tablets, smart TVs and printers)

what does WAN stand for?

wide area network

what do WANs do?

connect LANs that are in different geographical locations. (e.g. a business with offices in multiple different countries would need a WAN for all of their devices to connect together.)

why do organisations hire infastructure (e.g. communication lines) from telecommunications companies who own and manage the WAN?

because a WAN is much more expensive to set up than a LAN. 

how can WANS be connected?

using telephone likes (copper or fibre optic), satellite links or radio links.

what is the biggest WAN?

the internet

what does PAN stand for

personal area network

what do PANs do?

connect devices over a very short range.

What are PANs normally centred around?

A single user

What are PANs often used for?

transmitting between mobile/ wearable devices (e.g. smartphones, headphones, smartwatches)

What do PANs often use to connect devices?

common wireless technology (e.g. bluetooth)

what makes bluetooth so suitable for PANs?

signal is strong and has a short range, which is ideal for connecting devices in the same room.

Why are PANs considered handy?

They don’t require any extra hardware, just the devices themselves. This means that you can create a PAN on the move. 

What are the benefits of networking computers? (5)

• sharing files is easier as network users can interact with the same files between devices.

• the same hardware can be shared (e.g. printers) between multiple devices.

• you can install and update software on all devices at once, rather than individually

• communication over network is cheap and easy (e.g. by email)

• user accounts can be stored centrally, so users can log in from any device on the network.

what are the drawbacks of networking computers? (4)

• can be expensive to set up (often needs lots of extra hardware)

• can be vulnerable to hacking and malware, which can easily spread between devices in network.

• some are dependent on 1+ servers. If they fail, it can be disruptive for users.

• large networks are difficult to manage, may require hiring a specialist to maintain them.

what does NIC stand for?

network interface card

what is a NIC?

a piece of hardware inside a device.

What does a NIC do? (2)

• allows a device to connect to networks. 

• they exist for both wired and wireless connections.

what are switches used for?

connecting devices on a LAN

what do routers do? (2)

• transmit data between different networks.

• most commonly used to connect to internet

what does the choice of a cable used for a wired network depend on?

bandwidth, cost, and how far data needs to be transmitted.

fibre optic cables (4)

• transmit data as light

• high performance, expensive

• don’t suffer interference

• can transmit over very large distances at high bandwidth without loss of signal quality

what is bandwidth?

the amount of data that can be sent across a network in a given time.

what are CAT 5e and CAT 6 wires examples of?

ethernet cables.

what do ethernet cables contain?

copper wires which are twisted together to reduce internal interference.

why are ethernet cables commonly used in homes and offices to connect devices on a LAN? (2)

• cheaper than fibre optic cables

• have a decent bandwidth

what are coaxial cables made of?

a single copper wire surrounded by a plastic layer for insulation, and metallic mesh to reduce interference

advantage and disadvantage of using coaxial cables? (2)

• very cheap

• low bandwidth

what are WLANs?

wireless LANs.

what do wireless networks use to transmit data?

radio waves.

what do you need to set up a wireless network?

a WAP (wireless access point) device.

what is a WAP?

a switch that allows devices to connect wirelessly.

what is a hotspot?

a location where you can connect to a WAP.

 benefits of wireless networks (4)

• covenient as you can get your device to automatically connect to network.

• you can move around while connected to the network

• cheaper, better for environment as no hardware needed.

• easy to add more users to a wireless network - no extra hardware or complex setup needed.

drawbacks of wireless networks (4)

• less secure than wired - access points are visible to all devices, making vulnerable to hacking.

• limit on how far a wireless network can reach.

• generally has lower bandwidth

• less reliable than wired

what is a topology?

the layout of a network.

star topology (3)

• devices are connected to central switch/server that controls network.

• central switch allows many devices to connect simultaneously.

• star networks can be wired or wireless.

pros to star topology (4)

• if device/cable fails, rest of network is unaffected

• simple to add more devices since each has their own seperate cable.

• better performance as data goes straight from device to central switch.

• very few data collisions compared to other topologies.

cons to star topology (4)

• wires for each device (in wired networks) can get expensive for large networks.

• switch is expensive

• problem with switch = whole network affected

• limit to the amount of connections that can be made

what do bus topologies use to connect devices?

a single ‘backbone’ cable, called a bus.

why are terminators placed at the ends of the bus?

to stop data reflecting back along the bus?

what would happen if bus topologies didn’t have terminators?

reflected signals would cause interference and potentially make the network unstable.

pros to bus topology (3)

• network is unaffected if device fails

• isn’t dependent on central switch to keep it running.

• relatively cheap to set up compared to star.

cons to bus topology (3)

• data collisions are common, which slows network down.

• more devices added, higher likelihood of data collisions, making it unsuitable for large networks.

• if bus cable breaks, splits network into seperate parts. 

what is a protocol?

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

what do protocols cover? (3)

• how communication between two devices should start and end

• how the data should be organised

• what devices should do if data goes missing

how is data sent between networks split?

• into equal sized packets.

• Each contains extra information (e.g. destination, source address) and a checksum.

what is the purpose of a checksum?

to find errors.

what is a layer?

a group of protocols with similar functions.

what does it mean for layers to be ‘self contained’?

protocols in each layer do their job without needing to know what’s happening in the other layers. 

what is the 1st layer of the TCP/IP model? (4)

Link

• passes data over physical network.

• responsible for how data is sent, and for interpreting signals. 

e.g. Wi-Fi, Ethernet

What is the 2nd layer of the TCP/IP model? (3)

Internet

• adds IP addresses to data packets, directing them between devices and managing traffic. Used by routers.

e.g. IP

What is the 3rd layer of the TCP/IP model? (3)

Transport

• sets up communications between two devices, splitting data into packets and checking that they are correctly sent and delivered.

e.g. TCP, UDP

What is the 4th layer of the TCP/IP model? (4)

Application

• providing networking services to applications, e.g. turning data into websites

e.g. HTTP, HTTPS, FTP, SMTP, IMAP

what are the advantages of using layers? (3)

• breaks network communication into manageable pieces.

• Each layer can be changed without affecting the other.

• There are set rules for each layer - this ensures that hardware and software are universal.

what does HTTP stand for?

hyper text transfer protocol

what does HTTPS stand for?

HTTP secure

what does FTP stand for

file transfer protocol

what does IMAP stand for?

internet message access protocol

what does SMTP stand for?

simple mail transfer protocol

what is HTTP used for

used by web browsers to access websites and communicate with web servers.

how is HTTPS used?

a more secure version of HTTP. Encrypts all information sent and recieved.

how is FTP used?

to access, edit and move files between devices on a network.

How is IMAP used?

to retrieve emails from a server.

how is SMTP used?

to send emails and to transfer them between servers.

what are TCP and UDP

transport layer protocols which control the packing and unpacking of data.

what does TCP do?

establishes a connection between sending and receiving devices.

what does TCP do after establishing a connection between the sending and recieving devices?

splits the data into numbered packets that can be reassembled into the original data once they reach the destination.

what does the TCP do after splitting the data?

it communicates with the recieving device to make sure that all packets have been transferred correctly.

what happens if the packets haven’t been transferred correctly in TCP?

they can be resent. The sending device gets confirmation when the transfer is complete.

when is TCP suitable?

when you need a reliable connection, e.g. downloading files.

what can happen if data packets are missing?

it can lead to files being corrupted and unusable.

what does UDP do?

break the data down into packets without numbering them.

how are packets sent by UDP read?

in the order they arrived, even if it’s not in the order they were sent.

how many times does UDP send the packets?

once

what doesn’t UDP do? (2)

• check with the receiving device that everything has been received.

• This saves time, but there’s no way of knowing if packets have been lost in transit.

What is UDP suitable for?

applications that need fast, efficient transmission e.g. video streaming

what does internet protocol (IP) do?

operates on the internet layer, establishing connections between routers and handling network traffic.

What are IP addresses?

unique numbers assigned to every device connected to an IP network

where are IP addresses added?

to the header of each packet at the internet layer.

what is IP responsible for?

directing data packets to their destination across the internet or other IP networks using packet switching.

What does the way that the data is sent depend on?

The network traffic - so the packets can take different routes. 

what might happen if a router recieves too many packets at once?

it may prioritise some over others.

why is packet switching an efficient use of the network?

• because there are so many possible routes that each packet can take.

• with packet switching, packets can reach their receiving device quickly, even if there’s heavy traffic.

what is Wi-Fi?

a family of protocols commonly used in WLANs.

where does Wi-Fi operate?

on the link layer

what are units of data sent on the link layer called?

frames, instead of packets.

what two frequency bands does Wi-Fi use?

2.4GHz and 5.0GHz

What’s the benefit of Wi-Fi using 2.4 GHz?

It has a greater range and is better at getting through obstructions (e.g. walls)

What’s the benefit of Wi-Fi using 5 GHz?

it’s faster over short distances.

what can happen to networks using adjacent or overlapping channels?

They can cause interference.

What is ethernet?

a family of protocols that operates on the link layer.

what does ethernet do?

handles transmission of data between devices on LANs, but specifically for wired connections.