Packet Switching (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
Packet Switching
What is packet switching?
Packet switching is a method of sending and receiving data (packets) across a network
Packet switching can be broken down into five stages:
Stage | Overview | Detail |
|---|---|---|
1 | Data is broken down into packets |
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2 | Packets are assigned a header | |
3 | Each packet makes its way to the destination |
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4 | Routers controls the routes taken for each packet |
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5 | Packets arrive and are reordered correctly |
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What are the advantages of packet switching?
Interference and corruption are minimal as individual packets can be resent if they are lost or damaged
The whole file doesn’t need to be resent if a corruption occurs, this saves time and internet bandwidth
Packet switching is quicker than sending a large packet as each packet finds the quickest way around the network
It's harder to hack an individual's data as each packet contains minimal data, and travels through the network separately
Worked Example
A local market shop wishes to arrange a delivery of goods from a supplier. Anna, the shop owner, decides to send an email to request the delivery of the goods at a certain date and time.
Describe how packet switching is used to send this email and how it can be protected from corruption.
[8]
Answer
The business email is first broken down into packets which are given a source address (where it's come from) and a destination address (where it's going to) [1]
Each packet receives a packet number so that the email can be reassembled when it reaches its destination [1]
Each packet also receives an error check such as a parity bit. A parity bit checks whether any bits have been flipped due to corruption [1]
Each packet is sent over the internet via routers. Routers contain routing tables that determine the next closest router to the destination [1]
Packets may take different routes depending on internet traffic and arrive at their destination in any order [1]
Packets are checked for errors using the error checks and missing packets can be requested to be resent [1]
Once all packets have been received then they can be put together in order using the packet numbers [1]
Once assembled the original email can be read by the other business [1]
Examiner Tips and Tricks
For high marks make sure your answer is coherent, that is it follows logically from one point to the next.
Some marks depend on previous points you have made.
Explaining parity bits without mentioning error checking first may not gain you additional marks
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