This key facts covers What is a Packet? within Packet Switching for GCSE Computer Science. Revise Packet Switching in 3.5 Fundamentals of Computer Networks for GCSE Computer Science with 15 exam-style questions and 18 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
What is a Packet?
Structure of a Network Packet:
Each packet contains three parts: Header, Payload (Data), and Trailer.
1. Packet Header:
- Source IP address: Where packet came from
- Destination IP address: Where packet is going
- Packet number: Sequence number for reassembly (e.g., packet 3 of 10)
- Protocol information: TCP/UDP, etc.
- Time to Live (TTL): Prevents packets looping forever
2. Payload (Data):
- Actual data: The message/file content being transmitted
- Size: Typically 500-1500 bytes per packet
- Fragment of whole: Each packet carries small piece of total data
3. Packet Trailer (Footer):
- Error checking: Checksum or CRC (Cyclic Redundancy Check)
- Detects corruption: Identifies if packet was damaged during transmission
- Validation: Recipient can verify data arrived correctly
Practice questions for Packet Switching
Which of the following best describes packet switching?
Explain why packets from the same file can travel by different routes through a network. [2 marks]