Packet vs Circuit Switching

Circuit Switching

A dedicated path is established between sender and receiver for the entire duration of communication.

• Path is reserved before data flows.
• Resources are guaranteed but wasted if idle.
• Example: Traditional telephone (PSTN).

A ======================== B
   (dedicated path locked)

Packet Switching

Data is broken into packets, each routed independently through the network.

• No dedicated path.
• Resources shared among many users.
• Example: Internet (IP).

Packet 1 --- Router --- takes path A
Packet 2 --- Router --- takes path B
Packet 3 --- Router --- takes path A
             (reassembled at destination)

Comparison

	Circuit Switching	Packet Switching
Path	Fixed, dedicated	Dynamic, per packet
Setup	Required before transfer	Not needed
Bandwidth	Wasted if idle	Efficiently shared
Delay	Low, consistent	Variable (jitter)
Failure	Whole call drops	Packets reroute
Use case	Voice calls	Internet traffic

Key Insight: Packet switching wins for bursty traffic (web, email) because bandwidth is shared. Circuit switching wins where you need guaranteed latency (real-time voice).

Is Circuit Switching Still Used?

• Traditional circuit switching (PSTN) — being phased out. Most telecom moved to VoIP (packet switching).
• MPLS — used in ISP backbone networks, pre-establishes label-switched paths.
• VoIP with QoS — still packet switching but reserves bandwidth to mimic circuit switching.
• 5G network slicing — dedicated virtual "circuits" carved out of packet infrastructure.
• Most modern calls (WhatsApp, Jio, Airtel) are VoIP = packet switching.