1.4 WiFi and Wired networks Flashcards
What is a computer network?
A computer network is two or more computing devices connected together in order to share resources.
What is a network enabled device?
A device is said to be ‘network enabled’ when it is capable of joining a network.
What is a LAN?
A Local Area Network is a network that has two or more network-enabled devices connected within a fairly close geographical area.
Where may a LAN be used?
5
- Home
- Business Office
- Hospital
- Library
- School
What are some advantages of a LAN? (6)
- Users can log on from any workstation and still access all of their files
- Peripherals (printers etc.) can be shared between many users - reducing costs
- Resources and files shared by users - collaboration on projects
- Backups can be done centrally
- Software can be installed centrally
- Data transmitted quickly between networked computers
What are some disadvantages of a LAN? (6)
- Network failure (if server fails, no one can access files)
- Slow service if lots of users are logged on
- Viruses and malware could easily spread around the network
- Expensive to set up and keep running
- Requires specialist staff
- Security if users forget to log out
What are 6 measures to improve security of a LAN?
- Strong passwords that are changed every month
- Different access rights for different users (students , teachers etc.)
- Audit log (records who saved, deleted and changed records and files)
- Backups done at least once a day
- Encryption of data travelling around the netwok (especailly for hubs and wifi)
- Users should not be able to install software
What is a WAN?
A wide area network (WAN) connects two or more local area networks (LAN) that are in different geographical locations.
What can be used to connect offices close together?
A ‘leased line’ from a telecom company can be used to connect offices in different towns.
Why do companies normally hire a WAN from a major telecom company?
It is very expensive and complicated to set up and maintain.
What are four ways long distance communication by a WAN can be achieved?
- Fibre optic lines, including laying undersea cables
- Satellite communication links
- Leased telephone lines
- Microwave links
What are 3 advantages of WANs?
- Allow LANs to connect to one another
- Allows workers to collaborate over a wide ares, even across continents
- Allows files and data to be shared between LANs
What are 2 disadvantages of WANs?
- Can be expensive to hire a WAN service from the telecom operator
- If a WAN fails, it is beyond the control of the company to fix, because it is owned by a number of external suppliers
What is bandwidth measured in?
Bits per second (Kbps, Mbps or Gbps)
What is bandwidth?
How much data can be transferred over a connection in a given time
What is the contention ratio?
The ratio of users compared to available bandwidth
How might a business achieve a fast and reliable internet connection?
Paying a telecom company extra money for a low contention ratio connection
Compare the speeds of the two main categories of ethernet cables?
Cat-6 is faster than Cat-5
Compare the costs of the two main categories of ethernet cables?
Cat-6 is more expensive per metre than Cat-5
How do fibre optic cables transder data?
Fibre optic tables transfer data using light which is reflected along the inside of a cable
What is a disadvantage of fibre optic cable?
It is more expensive than ethernet copper cable
What is a backbone?
- A backbone joins together a number of LANs in the same building or as part of a WAN
- The backbone is expected to carry heavy data traffic.
How is Wi-Fi divided?
- There are two frequency bands (2.4GHz and 5Ghz)
* These bands are furhter divided into seperate channels
Why is using seperate channels a good idea?
• It reduces the interference caused by nearby devices
Compare the 2.4Ghz band to the 5GHz band
- 5GHz can carry more channels so it has a higher capacity
- 5GHz equipment is more expensive
- 5GHz has a shorter range -> faster over shorter distances
Why is the number of Wi-Fi channels limited?
It is regulated by law
Along with the choice of band and channel, what are three other factors that can affect Wi-Fi performance?
- Radio interference
- Being blocked by thick walls or floors
- There are a limited number of radio channels available, limiting the number of people can use the network at the same time
When describing network performance, what is an error?
When a binary 1 was sent, but a 0 was received, or vice versa
What are the two main causes of network errors?
- Interference
* Signal is too weak
What is the techinal word for delay?
Latency
Why does latency increase as the network size increases?
Every switch, cable and router adds latency to the connection.
What five things affect the performance of wired networks?
- Type of cable connection (Ethernet or fibre optic)
- Bandwidth available
- Contention ratio
- Error rates
- Latency
What four things affect the performance of wireless networks?
- Band chosen and number of available channels
- Interference from of wi-fi devices sharing channels
- Interference from non-wifi devices (of the same frequency)
- Physical layout (solid walls and distance)
Why are Wi-Fi networks cheaper than wired networks?
They only need a Wireless Access point to set up.
Which type of network allows more people to log in?
A wired network allows more people to log in that a Wi-Fi network.
Which type of network has a higher bandwidth?
A wired network (often >10Gbps)
Which type of network is more secure?
- Wired networks are more secure.
* Wi-Fi not as secure as connection is by radio
Which type of network is more portable?
- Wi-Fi is more portable as users can carry their laptop around and not lose connection
- Wired network are not portable as each computer needs to have a network socket available
Describe the layout of a client-server LAN arrangement.
Most files and data are stored on a server. All computer on the network connect to this server through a central hub or switch.
What are two names for the computer on a network?
- Workstation
* Client
Why isn’t a server needed on a peer to peer network?
The files are stored on the hard disks of individual network machines (e.g. in a shared folder)
Compare C-S networks to P2P networks in terms of technical skills needed.
- C-S network needs technical skill to maintain
* P2P needs little technical skill as operating systems have built-in support for network sharing
Compare the effect of a broken workstation on a C-S and P2P network.
- C-S: A broken workstation has no effect on the overall network.
- P2P: A broken or disconnected peer computer has an effect on all peers because their shared folder(s) are no longer available.
Where is the NIC?
It is built into the motherboard.
What is hardwired onto the NIC?
The MAC address.
What does MAC stand for?
Media Access Control.
As well as holding the MAC address, what is the NIC responsible for?
Converting data from the computer into the format used by the network and vice versa.
Explain 2 issues with hubs
- Data collisions are common because the hub relays the data packet it receives to every device on the network, slowing down the network.
- Security problems because someone could read data that wasn’t intended for them.
Which is more intelligent? Hub or Switch?
Switch
What does a hub/switch do?
Connects nodes on a network together.
What does a switch do that a hub doesn’t?
A switch only transmits the data packet to the node it was intended for.
Why do switches have better performance?
There are less data collisions.
Which has better security? Hub or switch?
Switch
Which is more expensive? Hub or switch?
Switch
What do switches use to transmit the data to the right device?
The MAC address.
What does a router do?
A router transmits data between networks by the most efficient route.
What are most home routers a combination of?
A router, a switch, and a WAP.
Why are ethernet cables in a ‘twisted pair’?
To reduce interference.
ISP stands for?
Internet Service Provider
URL stands for?
Uniform Resource Locator
How are IP addresses represented?
With four denary numbers from 0-255. Eg 36.153.62.136
What is the difference between static and dynamic IP addresses?
Static IP addresses are permamnent wheras dyanmic IP addresses are assigned when a device logs on to a network and can be different every time.
Who might use a static IP address?
A company that doesn’t want their IP address of their website changing.
Who might use a dynamic IP address?
ISP because they are more cost effective and can be reused.
What does DNS stand for?
Domain Name System
What does a DNS server do?
Translates a web address into the correct IP address for the server or service that you have requested.
What is the advantage of DNS?
You don’t need to remember any IP addresses of websites.
What is local hosting?
Hosting a website on your home PC.
2 advantages of local hosting?
- It costs less than external hosting
- If you are a web developer you can host a local copy of your site so you can test and update it properly before the site is uploaded to a public server
5 issues with local hosting?
- Bandwidth for local server will be your broadband connection (probably not enough)
- You’re computer always has to be on.
- If things go wrong, it requires technical knowledge to fix.
- It can be difficult to protect the website from malware and intrusion attempts.
- If you have a dynamic IP from your ISP, there is no permament IP address that can be used to connect to the server.
What will an external web hoster provide? (6)
- Hard disk space for your site
- Ensure that your site remains running
- Provide bandwidth
- Provide maintenance of the server
- Regular backups
- Security
What are the three types of external hosting?
Shared web hosting, dedicated server and virtual server.
What is the advantages of shared web hosting?
The cost is shared between users so it is cheaper.
2 disadvantages of shared web hosting?
- The websites share RAM and bandwidth, so if one website recieves heavy traffic the others will decrease in performance.
- You might have to accept advertising
2 advantages of a dedicated server?
- The websites performance is not affected by having to share with other sites.
- You get better support and more regular backups
Who would need a dedicated server?
Companies with a lot of website traffic.
What is the downside of dedicated servers?
They are more expensive than shared web hosting servers because the cost isn’t shared.
What is a virtual server?
A server than runs specialist software to run servers within itself.
Why is renting space in a virtual server cheap?
Many websites can be hosted on a singular server so the cost can be shared.
What is the cloud?
A range of software and services that run on the internet rather than on your PC.
5 advantages of the cloud?
- You can access your data from any device with an internet connection.
- Documents can be worked of simultaneously
- You redice the amount of storage needed on your home device
- Your work is automatically backed up
- You can access the latest versions of software
5 disadvantages of the cloud?
- No internet = no access
- You can’t access it if you forget your login details
- They sometimes require a monthly fee
- Data might not be sotred in UK –> data being subjected to different laws
- There is a risk of online hackers
What is used to make a virtual network?
Software
How do virtual networks work?
Some of the physical network’s bandwidth is partitioned off to form a seperate network.
3 advantages of virtual networks
- It is flexible because it is easy to add or remove computers using software instead of cables
- It is easier to install software for specific groups of people
- Improved security - if on VLAN is compromised with malware the others won’t be
Connecting a LAN to a WAN using a virtual network is called a…
Virtual Private Network
What is the encryption of data flowing through a VPN called?
VPN tunnelling
Why would you use a VPN instead of maintaining a WAN of your own?
It is much cheaper
How is a virtual network secure?
Each virtual network has its own security and firewall.
Some virtual networks can only be accessed with login information.
If one VLAN is compromised, the others will remain unaffected.
What is a VPN used for?
Sending data over a large network (Internet) securely
