Circuit switching vs packet switching

Circuit switching: a dedicated physical path (circuit) is set up between sender and receiver before data transfer, kept for the whole session, and released afterwards (e.g. the traditional telephone network).

Packet switching: the message is split into small packets, each carrying source and destination addresses. Packets travel independently, share links, and are reassembled at the destination (e.g. the Internet).

Basis	Circuit switching	Packet switching
Path	Dedicated path set up before transfer	No dedicated path; each packet is routed separately
Phases	Setup → data transfer → teardown	No setup needed (datagram) or a virtual circuit is set up
Resource use	Bandwidth reserved even when idle; poor utilisation	Links shared through statistical multiplexing; efficient
Delay	Setup delay, then constant, low delay	Variable delay due to queuing and routing
Order of data	Arrives in order on the same path	May arrive out of order (datagram); reordered at destination
Data unit	Continuous stream	Packets
Congestion	Blocked at setup time (busy signal)	Occurs during transfer (delay or packet loss)
Reliability	A failure breaks the call	Packets can be rerouted around failures
Header overhead	None per data unit	Every packet carries a header
Best for	Real-time voice with constant rate	Bursty data traffic (web, email, file transfer)
Cost	Higher	Lower
Example	PSTN telephone network	Internet (IP)

Circuit:  A ===== S1 ===== S2 ===== B     (one reserved path)
Packet:   A -> S1 -> S2 -> B,  A -> S1 -> S3 -> S2 -> B   (paths may differ)