Demonstrate a clear understanding of packet switching, its operation, advantages, disadvantages and how it differs from circuit switching.
Key Concepts
Circuit Switching – a dedicated communication path is established for the duration of a session.
Packet Switching – data is divided into packets that travel independently through the network.
Bandwidth – the maximum rate at which data can be transmitted, usually expressed in bits per second (bps).
Latency – the time taken for a packet to travel from source to destination.
Over‑head – extra bits added to each packet for addressing, error detection, etc.
How Packet Switching Works
Data is broken into small units called packets.
Each packet receives a header containing:
Source and destination addresses
Sequence number
Checksum for error detection
Packets are routed independently through the network, possibly taking different paths.
At the destination, packets are re‑ordered using sequence numbers and the original message is reconstructed.
Mathematical Representation
The effective throughput \$T_{\text{eff}}\$ of a packet‑switched link can be expressed as:
\$T_{\text{eff}} = R \times (1 - O)\$
where \$R\$ is the raw link rate (bits/s) and \$O\$ is the proportion of bandwidth used for overhead (e.g., headers).
Comparison of Circuit Switching and Packet Switching
Aspect
Circuit Switching
Packet Switching
Connection Type
Dedicated physical path for the whole session
Shared network resources; each packet routed independently
Resource Allocation
Reserved bandwidth for the duration of the call
Bandwidth allocated on a per‑packet basis; resources are used only while packets are in transit
Latency
Predictable, low after connection is set up
Variable; depends on congestion and routing decisions
Efficiency
Poor when the channel is idle (wasted capacity)
Higher overall utilisation; idle periods are filled by other traffic
Scalability
Limited – each new call requires a new circuit
Highly scalable – many users share the same infrastructure
Reliability
Stable once established; failure of a single link breaks the circuit
Resilient – packets can be rerouted around failed nodes
Typical Applications
Traditional telephone networks, some real‑time video links
Internet data traffic, VoIP, video streaming, email
Advantages of Packet Switching
Better utilisation of network resources.
Robustness to failures – alternate routes can be used.
Supports a wide variety of traffic types (burst, continuous, interactive).
Scales easily with increasing numbers of users.
Disadvantages of Packet Switching
Variable latency can affect real‑time applications.
Over‑head from packet headers reduces effective data rate.
Potential for packet loss; requires retransmission mechanisms.
Complex routing algorithms are needed.
Key Points to Remember
Packet switching divides data into packets, each with its own header.
Packets may travel different routes and arrive out of order.
Reassembly at the destination uses sequence numbers.
Over‑head reduces the net data throughput but provides flexibility and resilience.
Understanding the trade‑off between latency and utilisation is essential for network design.
Suggested diagram: A side‑by‑side illustration of a circuit‑switched path (single continuous line) versus packet‑switched routing (multiple arrows showing packets taking different routes).