Intro to Computer Science / Unit 9: The Internet and Networks
9.3 Packets and Routing
Notes
Data sent over the internet is split into small pieces called packets.
- Each packet has a header (with the source and destination IP addresses and a sequence number) and the data.
- Packets can take different paths and may arrive out of order. The receiving device uses the sequence numbers to put them back in order.
- Routers read the destination address and forward each packet toward its destination.
- The internet has many paths, so it is fault tolerant: if one router or cable fails, packets can be sent another way.
- Example: an email split into 12 packets may arrive as packets 3, 1, 2, ... and is reassembled in order 1 to 12.
Practice
What is a packet?
Messages are divided into packets that each carry address details.
What is the job of a router?
Routers pass packets along the best available path.
A cable in the middle of the network breaks, but a web page still loads using another path. This shows that the internet is:
Multiple routes mean data can be rerouted around failures.
Ready for more? Take the Unit 9 test.