Subtopic Notes

14.2 Circuit switching, packet switching

14. Communication and internet technologies

Circuit Switching

Method of communication where a dedicated physical path (or circuit) is established between two devices for the entire duration of a communication session
The links that make up the circuits are removed afterwards
The circuit has a constant bandwidth, regardless of usage
Example: Traditional telephone networks, Voice calls, Video Conferencing

Advantages	Disadvantages
Reliable and consistent data flow	Takes time to establish the circuit
Suitable for real-time communication (e.g., voice calls)	Wastes bandwidth if no data is being sent
Data arrives in order so it doesn’t need to be reassembled	Not efficient for bursty or low-volume data (like emails or browsing)
No delay once the circuit is set up	Less secure as it only uses one route
Data can’t get lost	No alternative route in case of failure
	Bandwidth can’t be shared

Method of data transmission where messages are broken into small units called packets, which are sent independently across a network
Ideal for data like emails, browsing, and file transfer
If there’s a missing packet, a request is sent to retransmit the data.
Data is broken down into packets to be transmitted
A packet of data contains
- Packet Header
  - Destination IP address
  - Packet serial number
  - Originator’s IP address
  - Packet Size
- Payload
  - The Actual data
- Trailer
  - A Method of identifying that it’s the end of packet
  - An error-checking method

Advantages	Disadvantages
Efficient use of bandwidth	Possible delays due to congestion
Scalable and flexible network use	Packets can arrive out of order
Robust against network failure (alternative routes possible)	Requires reassembly and error checking at the receiver
Communication is asynchronous¹	Packets might be lost (Packet loss)
Corrupt packets can be resent	Must wait until the last packet received to reassemble

Assigns IP Addresses to devices on local network
Checks the destination IP address of incoming data packets.
Utilizes routing tables to decide the next hop or router on the path to the destination.
Send the data packet to the designated next hop.
Routing table: Stores network ID, routing metric², Next hop³, Interface⁴

Packet Switching	Circuit Switching
No fixed path	Dedicated fixed paths
Data is sent in small packets	Data is sent as a continuous stream
Efficient: bandwidth is shared	Less efficient: bandwidth reserved even when idle
No setup required	Time required to setup
May be less reliable without error control	Reliable once connection is established
Delays due to routing and reassembly	Minimal delay after connection setup
Ideal for internet, emails, web browsing, file transfers	Ideal for real-time calls, like traditional phone systems
Resources used only when needed	Resources remain occupied throughout the session
Data needs to be rearranged	Data comes in order

Asynchronous communication: A method of communication where data is sent and received without requiring the sender and receiver to interact at the same time. ↩
Routing Metric: A value used by routing protocols to determine the best path to a network, based on factors like hop count, bandwidth, delay, or cost. ↩
Next Hop: The IP address of the next router a packet should be sent to on its way to the destination network. ↩
Interface: The local network connection (e.g., Ethernet port, Wi-Fi interface) through which the packet should be forwarded to reach the next hop or destination. ↩