Packet switchingMonil Adhikari

Packet Switching• Packet switching is the method by which the internet works, it features

delivery of packets of data between devices over a shared network. • For example the school web server sending you a webpage over the internet

or you sending an email to a friend.• To get from one device to another the data packets will have to travel

through network adapters, switches, routers and other network nodes.• The route taken by each packet might vary and at times there might be a lot

of data travelling through these nodes meaning packets will be queued.• This will result in varying times it takes to send data from one device to

another depending on the traffic load in the network.

Packet Switching (Contd.)• If you play computer games online you might have heard the term

latency (or lag), this is the time taken to send data from one device to another. • The higher the latency (time taken to send data), the less responsive

your game will be. People with very low latency tend to do better at games as their machines will be more responsive.

Packet Switching Steps• Data split into chunks (packets)• Each packet has a from address, to address and payload (data chunk)• If data requires multiple chunks then the order of each packet is noted• Packets sent onto the network, moving from router to router taking

different paths (set by the router). Each packet's journey time can therefore differ.• Once packets arrive they are re-ordered• Message sent from recipient to sender indicating that the message has been

received• If no confirmation message, sender transmits data again

Exercises

1. For the following packets (Green, Blue, Red), assuming each step from router to router takes an equal time. What order will the packets arrive at their destination? How do we make sure that the packets are read in the correct order?

2. What happens if a packet gets permanently lost on the way to a host?3. What happens if a router on the network fails? How will the packets get to their destination?

What happens if a router on the network fails? How will the packets get to their destination?

THANK YOU