Show Menu
Cheatography

Computer Networks - AQA Computer Science Cheat Sheet by [deleted]

What is a Computer Network?

A digital teleco­mmu­nic­ations network which allows nodes (i.e. computers) to share resources.

Pros and Cons of Networks

Advant­ages:
Commun­ication: becomes easier as a result of technology like texting, emailing, etc.
 
Flexib­ility: if inform­ation is stored on a network, it means users can access it from anywhere in the world.
 
Sharing resources: sharing files and inform­ation over a network, including software (can be streamed using web applic­ations) and access to printers.
Disadv­ant­ages:
Hardware: routers, network cards etc are required to set up a network. This is expensive and requires profes­sional expertise to set up.
 
Vulner­ability: hackers can break into networks. Malware can spread and damage files on many computers via a network.
 
Dependence: users relying on a network might be stuck without access to it.

Wired vs Wireless

Wired Networks
The computers are physically connected by wires (e.g. coaxial copper cables, fibre optics). They are arranged in topologies.
Wireless Networks
There is no physical connec­tion, as radio waves (e.g. in the form of WiFi) are used to commun­icate data instead.
Which is Better?
It is dependent on situation. Wired networks are more reliable, as there is less interf­erence. Security is also easier to manage. However, cabling and other physical components can make it very expensive. Wireless networks allow mobility and flexib­ility, but are much less secure and interf­erence can occur. Data transfer may also be slower.

Why is network security important?

Network security is a broad term for any measures that protect a network from unauth­orized access, misuse, destru­ction, or the sharing of confid­ential inform­ation. It is important because otherwise sensitive data may be shared or lost. It is also essential from a legal persep­ctive. For busine­sses, corporate espionage is another a potential issue.

Methods of Network Security

Authen­tic­ation
Checking the identity of a user, usually by requiring them to input a password or biometric ID.
Encryption
Encoding data it using a key, meaning that the same key is needed to decrypt the data. This is how HTTPS works.
Firewalls
Protects a network from unauth­orised access.
MAC Address Filtering
Allows devices to access or be blocked from accessing a network based on their physical address embedded within the device’s network adapter.

TCP/IP

TCP
Transmi­ssion Control Protocol, a protocol dictating how to establish and maintain a network conver­sation.
IP
Internet Protocol
TCP/IP
A 4-layer model that is essential to networ­king.
Applic­ation Layer
Where the network applic­ations, such as web browsers or email programs, operate. Examples: HTTP, HTTPS
Transport Layer
Sets up the commun­ication between the two hosts and they agree settings such as ‘language’ and size of packets.
Network Layer
Addresses and packages data for transm­ission. Routes the packets across the network.
Data Link Layer
This is where the network hardware such as the NIC (network interface card) is located. OS device drivers also sit here.

TCP/IP Diagram

 

Network Protocols

Ethernet
A family of protocols that dictate how devices on the same network segment format and transmit data.
Wi-Fi or WLAN
A family of protocols that deal with wireless transm­ission.
TCP
Transmi­ssion Control Protocol: splits (and later reasse­mbles) data into packets. Also involves error checking, as expects an acknow­led­gement transm­ission within a set time frame.
UDP
User Datagram Protocol:
IP
Internet Protocol: each device has an IP address. Packets are 'addre­ssed' to ensure they reach the correct user.
HTTP
Hypertext Transfer Protocol: used to access a web-page from a web server.
HTTPS
Hypertext Transfer Protocol Secure: u7ses encryption to protect data.
FTP
File Transfer Protocol: handles file uploads and downloads, transfers data and programs.
SMTP
Simple Mail Transfer Protocol: handles outbound email. SMTP servers have databases of user's email addresses.
IMAP
Internet Message Access Protocol: handles inbound emails.
A network protocol is a set of rules/­con­ven­tions that dictate how a network operates.

Network Topologies

What is network topology?
The way that a network is physically struct­ured.
What is star topology?
A network where there is a central server that all of the computers and periph­erals are connected to.
Advantages of star toplogy:
1. If a computer fails, there is no impact on the other devices.
2. Security is good, because the data only passes through the server, not any other devices.
3. There are no data collis­ions.
Disadv­antages of star topology:
1. If the server fails, it's a catast­rophe.
2. Lots of cabling is need to connect all the devices indivi­dually, so it's quite expensive.
What is bus topology?
A network where there is a central backbone of cable connecting every computer. At each end of the cable is a terminator to stop data from contin­ually being moved around.
Advantages of bus toplogy:
1. Cheap.
2. Easy to add more devices.
Disadv­antages of bus topology:
1. Only approp­riate for small networks, otherwise data transm­ission is too slow.
2. Data collisions are likely.
3. If the backbone is severed, all computers are impacted.

Bus Topology

Star Topology

Types of Network

PAN
Personal Area Network - a network comprising only a small number of devices belonging to only one individual (e.g. Blueto­oth).
LAN
Local Area Network - a network that encomp­asses a small area (e.g. one company's network).
WAN
Wide Area Network - a network comprising many devices and covering a large area (e.g. the Internet). Often under collective ownership.
       
 

Comments

Add a Comment

Your Comment

Please enter your name.

    Please enter your email address

      Please enter your Comment.

          Related Cheat Sheets

          Bio Topic 1: Cell Biology Cheat Sheet

          More Cheat Sheets by [deleted]