Packet & Circuit Switching (OCR A Level Computer Science)
Revision Note
Written by: Neil Southin
Reviewed by: James Woodhouse
Packet & Circuit Switching
What is Packetising?
Packetising is a process where a large message is divided into smaller, manageable units called packets
Each packet can then be sent individually over the network
Packet formation
When a message is too large to be sent as a single unit, it's divided into smaller packets
Each packet is typically composed of a header, payload (actual data), and a footer (or trailer)
Use of headers
Headers are important because they contain information necessary for the packet's delivery
Typical information in a header includes:
Source IP address: identifies the sender of the packet
Destination IP address: identifies the intended recipient of the packet
Sequence Number: helps in reassembling the packets back into the original message at the receiving end
Protocol: identifies the transport protocol (TCP, UDP, etc.)
Packet Length: indicates the size of the packet
Checksum: a value used for error-checking
Packet transmission
After being packetised and encapsulated with headers (and trailers), packets are transmitted individually across the network
Packets might take different routes to reach their destination
Packet reassembly
When the packets reach their destination, they are reassembled back into the original message using information in the headers
Packet switching
Packet switching is a networking communication method that breaks down data (large files, emails) into smaller packets, sends these packets separately along different routes, and then reassembles them at their destination
Benefits | Drawbacks |
|---|---|
Efficient use of network resources as packets can follow different paths to the destination, using more of the available bandwidth | Not ideal for real-time services like video calling or VoIP, which require a steady stream of data without delays |
More reliable, as if a single packet fails to reach its destination, only that packet needs to be resent, not the entire data stream | Packets can arrive out of order, requiring reassembly and error-checking |
Lower cost due to shared network resources | Potential for congestion in the network |
Circuit switching
Circuit switching is a communication method where a dedicated communication path is established between two devices for the duration of their conversation (like a phone call), and all packets are sent along the same route
Benefits | Drawbacks |
|---|---|
Ideal for real-time services, with a constant and steady data transmission rate | Less efficient, as resources remain allocated during the whole conversation, even when no data is being sent |
No delays as a dedicated path is established | It is more costly due to the dedicated line requirement |
Data arrives in order as it follows the same path | Less flexible and scalable, as adding new devices can be complexx |
Packet switching vs Circuit switching comparison table
Packet Switching | Circuit Switching |
|---|---|
Benefits | |
Efficient use of network resources as packets can follow different paths to the destination, using more of the available bandwidth | Ideal for real-time services, with a constant and steady data transmission rate |
More reliable, as if a single packet fails to reach its destination, only that packet needs to be resent, not the entire data stream | No delays as a dedicated path is established |
| Data arrives in order as it follows the same path |
Drawbacks | |
Not ideal for real-time services like video calling or VoIP, which require a steady stream of data without delays | Less efficient, as resources remain allocated during the whole conversation, even when no data is being sent |
Packets can arrive out of order, requiring reassembly and error-checking | More costly due to the dedicated line requirement |
Network congestion can lead to packet loss | Less flexible and scalable as adding new devices can be complex |
Summary table for Circuit and Packet Switching
| Packet Switching | Circuit Switching |
|---|---|---|
Definition | A mode of data transmission in which a message is broken into several parts sent independently, over whatever route is optimum for each packet, and reassembled at the destination. | A mode of data transmission in which a dedicated communication path is established between two devices through a network for the duration of their conversation. |
Data Transmission | Data is broken into packets and transmitted independently. | Data is transmitted in a continuous stream. |
Efficiency | High efficiency as network resources are shared and used as needed. | Lower efficiency as a dedicated path is maintained even when no data is being transmitted. |
Reliability | More robust against network failures as packets can be rerouted. | Less flexible in handling network failures as the dedicated path, once broken, needs to be re-established. |
Scalability | It is highly scalable as it can accommodate large amounts of data and many users. | Less scalable due to the need for dedicated paths for each communication. |
Use Cases | Best for data that can tolerate some delay, such as emails and web pages. | Ideal for real-time services, like voice calls or video conferencing, that require low latency. |
Examiner Tips and Tricks
Avoid talking about the speed of data transmission in an answer to a question on packet or circuit switching. This will not get you a mark in the exam and, in some questions, is explicitly stated as not worthy of a mark. It is better to talk about higher bit rates or bandwidth (the number of bits sent per second) or the efficiency of the transmission
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