13.3 EVOLUTION OF PACKET-BASED NETWORK ARCHITECTURES

The packet-switching principles introduced in the previous section have been implemented using a variety of network architectures over the past five decades. These architectures reflect the evolution of telecommunications as transmission media became progressively faster, more reliable, and less expensive.

Early public data networks were designed at a time when long-distance communication links were relatively slow and prone to transmission errors. As a result, considerable intelligence was incorporated into the network itself to detect errors, recover lost information, and control the flow of traffic. As digital transmission systems improved, these functions were progressively shifted away from the network and towards the communicating devices at each end of the connection. This allowed the network to become simpler, faster, and more efficient.

Three technologies clearly illustrate this evolution: X.25, Frame Relay, and Asynchronous Transfer Mode (ATM). Although all three have now largely been superseded by IP- and Ethernet-based networks, each introduced concepts that continue to influence modern communications systems.