1.11 Networks Flashcards
Networks, LAN & WAN
- Network: 2+ computers connected together, transmitting data between each other
- Local Area Network (LAN): Network spread over a small geographical area (E.g school)
- Wide Area Network (WAN): Network spread over a large geographical area. (E.g Offices in multiple locations, communicate between different sites)
Protocols
Protocol: Set of rules defining how two computers communicate. Standardised so all devices have a designated method of communication
- HTTP (Hypertext Transfer Protocol): Used for web page rendering, HTTPS (Encrypted)
- TCP/IP (Transmission Control Protocol / Internet Protocol): Networking protocol used in the routing of packets through networks
- POP3 (Post Office Protocol) & IMAP (Internet Message Access Protocol): Mailing protocols, used for email access.
- FTP (File Transfer Protocol): Used for the transmission of files over networks
TCP/IP Stack & Protocol Layering
Stack of Networking Protocols: Passing packets during communication
- Application Layer: Top of the stack. Specifies what protocol needs to be used. (E.g application is a browser, it would select HTTP)
- Transport Layer: Uses TCP to establish end-to-end connection between source & recipient computer. Splits data into packets & labels these packets w/ packet no., total no. of packets & the port number used for communication
- If any packets get lost, transport layer requests retransmissions of these lost packets
- Network Layer: Adds the source & destination IP addresses
- Routers operate on the network layer and the router is what uses the IP addresses to forward the packets.
- Sockets are then used to specify which device the packets must be sent to & the application being used on that device.
- Link Layer: Connection between the network devices, adds MAC address identifying the Network Interface Cards of the source and
destination computers.
- For devices on the same network, the destination MAC address is address of the recipient computer, otherwise, it will be the MAC address of the router.
DNS
Domain Name System (DNS): System used to name & organise internet resources. Hierarchy, smaller domain separated from larger domain by full stop. (E.g ‘leeds.gov.uk’)
- TLDP: Top Level Domain, 2LD: 2nd Level Domain.
- Domain names easier to remember than IP addresses, used to link to servers across the world
- Role of DNS server to* translate domain names to IP addresses* to access a website
Data Packets
Data Packets: Segments of data, containing various information
Packet Header Information:
- Sender and recipient IP addresses for correct delivery and traceability.
- Protocol specification for interpreting the packet’s data.
- Packet order information for reconstruction at the recipient’s end.
- Time To Live (TTL) or Hop Limit to prevent eternal packet circulation.
Payload:
- Raw data to be transmitted.
Packet Trailer:
- Checksum or cyclic redundancy check.
- Detects transmission errors in the data.
Packet Switching
Packet Switching: Data communicated using packets across a network, across the most efficient route, can vary for each packet
Adv: Multiple methods to ensure data arrives intact (E.g. checksums, redundancy checks)
- Multiple routes can be used between devices, if one path breaks, another can be used
- Can be transferred over large networks, allows global communication
Disadv: Time spent deconstructing & reconstructing the data packets
- Must wait for all packets to arrive before data can be receive
Circuit Switching
Circuit Switching: Direct link created between 2 devices, maintained for the duration of the entire conversation between devices. Requires 2 devices to transfer & receive data at same rate
Adv: Data arrives in logical order, results in quicker reconstruction of data
- Enables 2 users to hold call without delay in speech
Disadv: Bandwidth is wasted when no data is being sent
- Devices must transfer & receive data at the same rate
- Using switches means electrical interference may be produced which can corrupt/destroy data
Firewall
Firewall Basics: Prevents unauthorized network access.
- Comprises 2 NICs between user and the Internet.
- Compares packets against preset rules (packet filters) set by the firewall software
Packet Filtering: Controls network access based on administrator rules.
- Examines source & destination IPs, protocols, and requested ports.
Actions of Firewall:
- Denial of access: Packet can be either dropped or rejected
- Rejected packet: Alerts the sender of the error
- Dropped packet: Occurs silently without any notification
Proxies
Proxy Server: Acts as an intermediary, collecting and sending data on behalf of the user
- Protects privacy, user remains anonymous
- Proxy server can cache frequently-used website data, making it faster to load
- Reduce overall web traffic
- Used by admins to prevent access (E.g school)
Encryption
Encryption: Way of keeping data secure when transmitting over the Internet
- Makes data unreadable if intercepted
- Data encrypted & decrypted using set of keys
Network Hardware
Network Hardware Overview: Essential hardware components for network maintenance
- Some built into devices, while others are standalone.
Network Interface Card (NIC): Connects devices to networks
- Assigns unique MAC address (usually a 12-digit hexadecimal number) to each device
Switch: Directs data flow in a network, commonly in star topologies.
Wireless Access Point (WAP): Connects devices to a network, often combined with a router for internet access.
- Commonly used in mesh networks.
Router: Connects multiple networks, enabling home networks to access the Internet.
Gateway: Used when networks have different protocols.
- Translates protocols to facilitate communication by removing and adding packet headers.
Client Server Network
Client-Server Networks: Terminals (clients) connected to a server (powerful central computer)
- Server holds all important information & resources
- Greater processing power than the terminals
- Clients request to use the server
Adv:
- More secure as data is stored in one location
- Central backups are carried out, no need for individual backups
- Data & resources shared between clients
Disadv:
- Relatively expensive to set up
- Dependant on the server
- Trained staff required to maintain server
Peer-to-Peer Network
Peer-to-Peer Networks: Computers connected to each other so that they can share files. Each device acts as both a server & client, provides & requests resources
- Used in piracy, impossible to trace origin of files
Adv:
- Cheaper to set up
- Allows users to share resources
- Easy to maintain
- Not dependent on a central server
- Specialist staff are not required
Disadv:
- Impossible to trace the origin of files
- Backups must be performed separately
- Poorer security
- May be difficult to locate resources
