elay, and jitter because of its store-and-forward nature Network intelligence Centralized Decentralized Bandwidth efficiency Packet loss Low to high, depending on the network The PSTN Versus the Internet In one very important fashion, the PSTN and the public Internet are one and the same thing: They both exist on the same physical infrastructure. There would be no Internet without the PSTN. The communications links, or backbones, that ISPs run on are delivered over the PSTN, and the access lines for entry into the Internet are all subscriber lines that are part of the PSTN. But what differentiates the PSTN and the Internet is the equipment attached to each network, its use, and how it for- mats the information it carries. PSTN Characteristics The PSTN basically includes telephones, fax machines, and circuit switches that set up continuous but temporary connections. In the PSTN, a circuit is established between two subscribers and kept open for the duration of the call, including peri- ods of silence. This provides guaranteed QoS and minimal latencies, and it means that the PSTN is optimized for voice and other real-time applications. It also means that the PSTN uses bandwidth inefficiently, making services more expensive. But The PSTN Versus the Internet we are constantly finding ourselves able to provide more bandwidth and derive more channels over that bandwidth. Internet Characteristics The Internet basically includes clients, which are the user interface and the input/ output device for information; servers, which are the centralized repositories of wisdom that you are seeking; and packet switches, which route the packets of information between the clients and servers. Whereas the PSTN connects two sub- scribers, the Internet connects networks. As on the PSTN, messages on the Inter- net are routed to specific end devices. These messages take various forms, such as e-mail, instant messaging, and real-time audio/video communications. Unlike the PSTN, however, the Internet breaks down a message into packets of d