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A-Level CS Flashcards: Networks

Computer Science — Networks Flashcards

20 interactive flashcards for A-Level Computer Science. Press Space to flip, rate 1-4.

What These Flashcards Cover

These flashcards test your understanding of how computers communicate over networks, the protocols that govern this communication, and the security measures that protect data.

Key areas:

  • Network Types: LAN (Local Area Network): small geographical area, high speed, privately owned. WAN (Wide Area Network): large geographical area, uses leased telecommunication lines. The internet is the world’s largest WAN.
  • Network Topologies: Star: all devices connect to a central hub/switch. Reliable (one failure doesn’t affect others) but hub is a single point of failure. Bus: all devices share a single cable. Simple but a cable failure brings down the whole network. Mesh: every device connects to every other device. Very reliable but expensive.
  • Client-Server Model: The server provides resources (files, websites, email). The client requests services. The server is in standard practice more powerful and always on. Peer-to-peer: all devices are equal, each can act as client and server.
  • TCP/IP Protocol Stack: Application layer (HTTP, FTP, SMTP, DNS), Transport layer (TCP for reliable delivery, UDP for fast delivery), Internet layer (IP for addressing and routing), Network access layer (physical transmission).
  • IP Addressing: IPv4: 32-bit address (e.g. 192.168.1.1). Subnet mask divides the address into network and host portions. NAT translates private addresses to public addresses. IPv6: 128-bit address to address the shortage of IPv4 addresses.
  • Web Technologies: HTML (structure), CSS (presentation), JavaScript (behaviour). HTTP (transfer of web pages), HTTPS (encrypted transfer), FTP (file transfer), DNS (domain name to IP resolution).
  • Network Security: Threats: malware, phishing, DDoS, man-in-the-middle attacks. Defences: firewalls, encryption (symmetric and asymmetric), authentication (passwords, biometrics, two-factor), access control lists.
  • Packet Switching: Data is split into packets, each routed independently. Each packet contains a header (source/destination address, sequence number) and payload. Routers forward packets based on destination IP.

Intuition

Think of a network like a postal system. Your letter (data) is put in an envelope (packet) with a destination address (IP address). The post office (router) reads the address and forwards it to the next post office until it arrives. TCP is like registered post — it confirms delivery and re-sends if lost. UDP is like regular post — fast but no guarantee of delivery.

DNS is like a phone book for the internet. You type “google.com” (the name), and DNS looks up the IP address (the number) so your computer can connect.

Common Pitfalls

  1. Confusing TCP and UDP. TCP is reliable (acknowledges receipt, re-sends lost packets) but slower. UDP is fast but unreliable (no acknowledgements). Use TCP for file transfers and web pages; use UDP for live streaming and gaming.
  2. Confusing hubs and switches. A hub broadcasts to all ports. A switch sends only to the intended recipient’s port. Hubs are obsolete; switches are the standard.
  3. Forgetting that encryption does not prevent interception. Encryption ensures that intercepted data cannot be read. It does not prevent the interception itself. You still need firewalls and access controls to prevent unauthorised access.
  4. Mixing up symmetric and asymmetric encryption. Symmetric uses one shared key (fast, but key distribution is a problem). Asymmetric uses a public/private key pair (slower, but solves key distribution). In practice, both are combined (asymmetric to exchange a symmetric key, then symmetric for the data).

See Also