Why can packet-switched networks continue working when one route fails?

Packet-switched networks are designed with high fault tolerance, allowing them to remain operational even when specific routes fail. Unlike circuit-switched networks, which rely on a single, dedicated physical path, packet-switched networks break data into smaller units called packets.

These packets can be directed down multiple paths through the network. If an outage occurs on a particular path, the network’s switches automatically reroute the packets along alternative available paths to reach their destination. This capability was a primary design goal for early researchers like Paul Baran, who sought to create a communications system capable of functioning even during catastrophic events, such as a nuclear attack.1

Because packets may take different routes, they can arrive at the destination out of order. To ensure the original data is reconstructed correctly, the packets are numbered and reassembled at the receiving end.21