Full Syllabus Audit: Swasti IGCSE CS: Chapter 2 Communication & Internet (Merged)
CS Chapter 2: Communication &
Internet
Transmission Methods, Error Detection, and Packet Switching
Final Combined Version for 1st Position Candidates. ļæ½ļæ½ļæ½ļæ½
1. Data Transmission Fundamentals
1.1 Direction and Method
ā¢Simplex: One direction only. | Half-Duplex: Both directions, not at once. | Full-Duplex: Simulta-
neously both directions.
ā¢Serial: One bit at a time over a single wire. High reliability over long distances (no skew).
ā¢Parallel: Multiple bits sent at once over multiple wires. Faster but prone to Data Skew (bits arriving
out of sync) over distance.
ā¢USB (Universal Serial Bus): A modern serial standard. Features: Plug-and-play, high-speed, and
power delivered through the cable.
2. Error Detection Logic
ā¢Parity Check: Adds a bit to make the count of 1s even or odd. If the count changes, an error occurred.
ā¢Checksum: A value calculated from a data block and sent with it. Receiver re-calculates to compare.
ā¢ARQ (Automatic Repeat Request): Uses acknowledgments and timeouts. If a NACK (negative
acknowledgment) is sent or time runs out, data is re-sent.
ā¢Check Digit: Used for human entry (e.g., barcodes) to detect transposition errors.
3. Packet Switching: The Journey of Data
How Data Moves (The 6-Mark Chain)
1. Data is broken into small Packets. Each has a Header (IPs, Sequence Number), Payload, and
Trailer (Checksum).
2. Packets are sent onto the internet and travel independently.
3. Routers guide packets via the fastest routes to avoid congestion.
4. Packets arrive at the destination out of order.
5. The receiver uses Sequence Numbers to reassemble them correctly.
6. If a Checksum fails, the packet is requested again via ARQ.
4. Internet and Browser Protocols
ā¢IP Address: Dynamic address identifying a deviceās location on a network.
ā¢MAC Address: Permanent, unique Hex address assigned to the NIC (Hardware).
ā¢DNS (Domain Name System): Translates human-readable URLs (google.com) into machine IP
addresses.
ā¢Cookies: Text files stored by the browser to remember user settings, logins, or track habits.
ā¢HTTPS: Secure version of HTTP that uses Encryption (SSL/TLS) for data security.
1
