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
• It sends these packets separately along different routes, and then reassembles them at their destination

Packet switching demonstration

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 complex

Packet switching vs circuit switching

Feature	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.
	Highly flexible and scalable; robust against network failures.	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 (jitter).	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 at the destination.	More costly due to the requirement for a dedicated line.
	Network congestion can lead to packet loss, requiring retransmissions.	Less flexible and scalable, as adding new devices can be complex and requires resource allocation.

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