 is per- formed depends on the generation of the network. With X.25, error detection and correction was a necessary feature of the network because the links were almost all analog and had high error rates. A provision of X.25 was to detect and correct for errors while they were in transport, hence improving data communications. But as networks became more digital and fiber based, noise became less of a problem; thus, the subsequent gener- ations of packet switching-Frame Relay and ATM, for instance-give the end- points the responsibility for error detection and correction. Not having to stop packets and investigate them in the throes of transmission greatly decreases the delays that would otherwise be encountered. Of course, today this is not so much a problem because there are fast processors and hardware to assist in this. In a connection-oriented environment, a virtual circuit defines the path end-to-end, and all packets follow the same path throughout the course of the session. As discussed in Chapter 3, the connectionless environment (which includes X.25 networks, the public Internet, private IP-based backbones, and LANs) can be likened to the postal service, in which a message is relayed from point to point, with each relay getting one step closer to its ultimate destination. In a connection- less environment, each packet of a message is an independent unit that contains the source and destination address. Each packet is independently routed at each intermediate node it crosses. The more hops it goes through, the greater the accu- mulated delays, which greatly affects delay-sensitive applications, including any form of real-time voice, real-time audio, real-time video, video-on-demand, and streaming media. But connectionless environments can work around problems, which is why they were so strong in the early days, when there were frequent sys- tem failures and links that were too noisy to perform correctly. Connectionless packets could circumvent system failures or noisy conditions and still meet at the Pac