Computer Science · Topic 2 · Data transmission
Packet switching. Send a message.
Your message is broken into numbered packets that race across the network by different routes, arrive out of order, get lost and resent — and are still reassembled perfectly at the other end. Watch it all happen.
0478 Topic 2 — Data transmission
packets · headers · routing · reassembly
Variables
5
10
1.0
Transmission stats
Packets sent
0
Arrived
0
Lost → resent
0
Out of order?
–
Each packet header carries the destination address and a packet (sequence) number so the receiver can put the message back in order.
📋 How packet switching works
- The message is broken into packets: header + payload + trailer.
- The header holds the destination address, the source address and the packet number.
- Each router reads the destination address and forwards the packet along the best route available at that moment — so packets from one message can take different routes.
- Packets can arrive out of order; the receiver uses the packet numbers to reassemble the message.
- If a packet never arrives, it is requested again and retransmitted.
⚖️ Benefits and drawbacks
- ✓ The network routes around busy or broken links, so delivery is reliable.
- ✓ Lines are shared efficiently — no single route is tied up by one message.
- ✗ Packets must be reordered at the destination, which takes time.
- ✗ Lost packets cause delays while they are retransmitted.
🎯 Syllabus reference (0478)
- Topic 2 — Data transmission: structure of a packet (header, payload, trailer); the contents of a packet header; how packet switching transmits a message across a network, including reordering at the destination.