Packet switching

Last time

Before we start: last time, in Data packets, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Many roads to one place

Think of driving across Lahore: there are many roads to the same place. The internet is the same: many routes between two computers. Packet switching lets every packet find its own route.

The picture

Here the sender splits the data into packets. Packet one goes through routers one and four. Packet two goes through two and six. Packet three goes through three and five. They all arrive at the same receiver.

Step by step

Here are the steps. The data is split into packets, and each one gets a header. Each packet is sent separately, and can take a different route. Routers read the destination address and send each packet on towards it.

Step by step

Because the routes are different lengths, and some are busier, the packets can arrive out of order. The receiver puts them back in order using the packet numbers. If a packet is missing, the receiver asks for it to be sent again.

The router

A router is the device that controls the route. It reads the destination IP address in the packet's header, and sends the packet on towards its destination, along the best route available at that moment.