packet switching

Imagine a shared highway with no reservations: anyone can put a car on it at any moment, and the road simply carries whatever shows up, sorting it out at each junction. Packet switching is networking done this way. Data is chopped into packets, and each packet is sent into the network independently, sharing the links with everyone else's packets on a moment-to-moment basis. No path is reserved in advance.

Here is the mechanism. A host breaks a message into packets, each carrying the destination address, and hands them to the network. Each packet travels store-and-forward: a router receives the whole packet, reads its address, and forwards it on the best outgoing link toward the destination. When several packets want the same link at once, the extras wait in a queue. Because links are shared on demand, the same link can carry many conversations interleaved — this is statistical multiplexing, and it is why packet switching uses capacity so efficiently for the bursty, on-off traffic that computers generate.

The trade-off is honest: packet switching gives no guaranteed bandwidth or delay. If everyone sends at once, queues grow, delay rises, and packets may be dropped — congestion. The alternative, circuit switching, reserves a fixed path and rate per call (great for guarantees, wasteful when idle). The Internet chose packet switching because computer traffic is bursty and the efficiency and resilience win out; the price is that quality-of-service and congestion control must be added back where guarantees are needed.