Packet Switching
1. What is a Packet?
Data is too large to be sent as one single block. Instead, it is broken down into smaller units called Packets. Each packet contains three distinct parts:
Packet Header
Payload (Data)
Packet Trailer
| Part | Contents |
|---|---|
| Header | Sender's IP, Receiver's IP, Packet Number (Sequence), Packet Size. |
| Payload | The actual piece of data (e.g., part of an image or email). |
| Trailer | End-of-packet marker, Error checking data (Checksum). |
2. The Process of Packet Switching
This is the step-by-step method used to send data across a network like the Internet:
1. Data is broken down into small packets.
2. Each packet is given a header (IPs and sequence number) and a trailer.
3. Packets are sent onto the network.
4. Routers inspect the IP address and decide the fastest path for each packet.
5. Packets may take different routes depending on network traffic.
6. Packets arrive at the destination, often out of order.
7. The receiving computer uses the sequence numbers to reorder them.
8. If a packet is missing or corrupted (detected via Checksum), a request is sent to re-send it.
The Role of the Router: A router is a node that connects networks. Its job is to look at the destination IP address of a packet and send it to the next node on the most efficient path.
3. Benefits and Drawbacks
- Benefit: Very efficient use of the network (no single line is tied up).
- Benefit: If one path is blocked or goes down, packets can be rerouted.
- Drawback: Packets can be lost or delayed (latency).
- Drawback: Not ideal for real-time applications like high-quality voice calls where "jitter" (out-of-order arrival) causes issues.