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1.3.3
| Question | Answer |
|---|---|
| Networks | Two or more devices connected together to allow data sharing |
| Standalone machine | single computer not connected to anything else |
| Networks pros and cons | Pros -Share files + peripherals -Access other devices' files -Servers control security, updates + backups -Communication Cons -More security risks -Malware spread easily -Server fails = devices connected fail -lots of data travelling=slow |
| Standard | sets of hardware and software specifications that allow manufacturers to create compatible products and services (e.g. character sets, HTML) |
| Protocols | Ensure technology-based standards and allow communication. - FTP - TCP - IP - UDP - POP3 - IMAP - SMTP - HTTP - HTTPS |
| FTP | (file transfer protocol): sends files between devices |
| TCP | (transmission control protocol): provides error-free transmission between two routers |
| IP | (internet protocol): routes packets across a WAN(wide area network) |
| UDP | (User Datagram Protocol): sends short messages where speed is more important than accuracy, without error-checking |
| POP3 | (post office protocol 3): retrieves emails from a mail server, deletes them from the server, and transferring them to your device |
| IMAP | (internet message access protocol): transfers emails to your device from the server, but keeps them on server until you delete them |
| SMTP | (simple mail transfer protocol): sends emails + transfers them between servers |
| HTTP | (hypertext transfer protocol): communicates between a web client and web server, sharing resources |
| HTPS | (hypertext transfer protocol secure): HTTP, with encryption + authentication |
| protocol suite | a set of protocols designed to work together (e.g.TCP/IP) |
| Layering | to divide the complex task of networking into smaller, simpler tasks that work together. Each layer provides a service to the layer above, only communicates with the layer before and after and is easy to maintain without thinking of whole stack |
| protocol stack | layering using protocols |
| TCP/IP stack | Four layers: Application Transport Internet/Network Link The sender's data goes from application to link and the receiver goes the other way and decapsulates (removes data) so the message can be read. |
| Application (TCP/IP stack) | packages data e.g. HTTP(S), FTP, SMTP, IMAP |
| Transport (TCP/IP stack) | sets up connections with servers/other devices, splits data into segments e.g. TCP, UDP |
| Internet/Network (TCP/IP stack) | uses IP addresses to route the data to its destination e.g. IP |
| Link (TCP/IP stack) | passes data to physical network, with cables or wireless, MAC address added e.g. wi-fi, ethernet |
| IP address | shows where the device is Computers are identified by IP addresses. The two most used IP systems are - IPv4 - IPv6 |
| MAC address | media access control: shows who the device is - 6 pairs of 2-digit hex numbers separated by colons |
| DNS | (domain name system): Hierarchical naming system by which devices on the internet or a private network can be identified. |
| URLs | Computers are identified by IP addresses. The two most used IP systems are |
| IPv4 IP addresses | four 8-bit numbers in denary, split by dots |
| IPv6 IP addresses | eight 16-bit numbers in hexadecimal, split by colons |
| URL typed into web browser | 1.Sent to DNS resolver; checks cache for IP 2.If not, queries DNS root name server, gets address of TLD 3.Checks TLD for IP address 4.If not: gets directions to another server 5.Finally; reaches name server that holds IP address. Saved in cache. |
| TLD | top-level domain |
| LANs + WANs | The two broad categories of methods computers are connected to in a network |
| LAN | local area network: - Connected over a small geographical area, usually at a single site - Network equipment typically owned by user of network - Typically connected using UTP cable, fibre optic, wifi |
| LAN pros and cons | Pros - Users have direct control - Cheap to set up; less devices - High data transfer speeds; less distance Cons - Users responsible for network upkeep - Devices only communicate with each other |
| WAN | wide area network (e.g. internet): - Over a large geographical area - Can, often does, consist of several LANs connected - Hardware usually not owned by users - Typically connected by telephone lines, fibre optic cables, satellite links |
| WAN pros and cons | Pros - Organisation leasing hardware responsible for upkeep - Global scale communication Cons - Slower data transfer speeds - Increasing security risk - More expensive; more hardware |
| Packet and circuit switching | Two ways of sending data across a network |
| Circuit switching | A physical, temporary and dedicated connection created between the two devices, that stops when they have finished communicating and cannot be used by others when they are |
| Circuit switching steps | 1. Connection established 2. Data transferred doing fixed pathway of nodes 3. Connection released |
| Circuit switching pros and cons | Pros - Competing users don’t degrade connection quality - Reliable connection Cons - Many applications don’t fully utilise available bandwidth |
| Packet switching | (more common) Divides data into packets: - Header - Payload - Trailer Packets sent along shortest latency May arrive jumbled (taken different routes) - sequence number used If packet's 'lost in transmission', receiving device requests a number |
| Packet switching pros and cons | Pros - More affordable, less complex infrastructure Cons - Some packets may arrive later then others |
| Threats | - Hacker - Malware - Social engineering - DOS - SQL |
| Hacker (threats) | person who attempts to gain access to a computer system with the intent of damaging data or somehow harming that system |
| Black-hat hackers | gain unauthorised access to computer system and cause damage |
| Grey-hat hackers | Attempt to locate flaws in a system unauthorised, then blackmail the company with it |
| White-hat hackers | security hackers authorised to try to find vulnerabilities in a system |
| Malware | software designed to damage a computer system - Virus - Worms - Trojan horse - Spyware |
| Virus (malware) | copy themselves when a file is open, attached to a file |
| Worms (malware) | rapidly duplicates so it can spread across a network |
| Trojan horse (malware) | malware disguised as legitimate software |
| Spyware (malware) | secretly obtains information about a user by transmitting data from their device |
| Social engineering | using people as the weakest link - Phishing - Pharming |
| Phishing (social engineering) | email/message sent to people to gain personal information with a hyperlink |
| Pharming (social engineering) | malicious code installed on a device misdirects users to fraudulent websites |
| DOS | Denial of service: a server is flooded with useless traffic, causing overload. |
| DDOS | distributed DOS: is more organised, several devices attacking at once |
| SQL injection | malicious SQL entered into an input field to gain control of a database |
| Security | prevents threats; aims to only allow authorised users access to what they need, prevent unauthorised access + minimise potential damage caused by unauthorised access |
| Firewalls (security) | monitors traffic going into or out of the network according to a set of rules. - Can be hardware or software (usually hardware) - Can block certain ports/traffic, and inspect data travelling through to see if it looks suspicious |
| Anti-malware software (security) | check files to see if they are contaminated |
| Proxy (security) | physical device between a network and remote source that packets must get through. If they are on the banned list, they will not get through |
| Encryption (security) | process of making data unreadable to a third party. - Stored data is encrypted in memory (usually symmetric) - Encrypted in transmission (usually asymmetric) |
| NIC (network hardware) | (network interface card): - Allows a computer to connect to a network - Works with a specific network standard - Each assigned MAC address assigned by manufacturer |
| Router (network hardware) | - Forwards packets between two networks to correct IP address - Connects networks to internet/other networks - 1 port connects to modem, other devices connect wirelessly |
| Hub (network hardware) | (not used as often, lack of security): - Connects severals devices together on a network - Broadcasts all data to all devices; only the receiving one should accept |
| Switches (network hardware) | - Connects devices to a network - Sends data to correct device - Much faster then hubs |
| WAP (network hardware) | (wireless access point) - Creates a wireless LAN by transmitting + receiving radio signals to devices with a wireless NIC - Connects to wired router, switch, hub via ethernet cables - Limited range (can be obstructed) + speed, but more convenient |
| Modem (network hardware) | Converts data between digital (for networks) and analogue (for cables) format (and vice versa) |
| Transmission media (network hardware) | - UTP cables - Coaxial copper cable - Fibre-optic cable - Wireless connections |
| UTP cables (transmission media) | (unshielded twisted pair) - Copper cabling - Twisted conductors to reduce electrical interference - No shielding (other than plastic insulation) - Relativity cheaper + faster then coaxial cable - Can be affected by external magnetic fields |
| Coaxial copper cable (transmission media) | 4 layers (in to out): 1. Thin copper wire 2. Plastic insulation 3. Wire mesh 4. Rubber layer - Short distances and is highly resistant to electrical interference - More expensive than UTP |
| Fibre optic cable (transmission media) | (more for across countries) - Light shone in one end, is reflected to the other and received by another device - Little energy loss over extremely long distances - Much more expensive |
| Wireless connections (transmission media) | increasingly more popular, allows flexibility but slower + weak range |
| Network architectures | Other ways to divide networks; define whether devices on a network can provide a service, access a service or both |
| Client-server (network architecture) | Consists of a client and server. Each client is connected to one central server, that may be connected to a switch and router for Internet access. Best for organisations with many computers that need to access the same information. |
| Client (client-server) | device that requests services from servers, and if authorised provided with the requested data |
| Server (client-server) | a device that provides a resource that can be accessed by authorised clients, typically always on, allowing 24/7 access Servers may provide: - File storage and access - Printing - Internet access - Email services - Regular backups of data |
| Client-server pros and cons | Pros - Easier to manage file security - Easier to install software updates - Easier to backup shared data Cons - Server is a point of failure - IT specialists maintain network - Server may be overloaded with requests |
| Peer-to-peer (network architecture) | Each device has equal status - can provide and request resources from others Each device connected to each other, allowing communication without central server Best for organisations with less computers where fewer users need access to the same data |
| Peer (peer-to-peer) | computer connected to the network, that is responsible for its own data and backup |
| Peer-to-peer pros and cons | Pros - Cheap and easy to set up/maintain - No single point of failure - No specialist staff needed Cons - Copies of files may be made - Each device backed up individually - Network is less secure |
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