ata, whose routing information guides the packets to their destination. Individual packets may take different routes, but they are reassembled in the proper order at the destina- tion. This system is optimal for the most efficient use of transmission facilities, par- ticularly when you're supporting bursty traffic that involves long periods of silence. In turn, this results in less expensive services. However, the tradeoff is that you get only best-effort QoS. Progress is being made on introducing QoS to the Internet, though, and in the next two or three years, this will change more. However, note that there is greater progress in introducing QoS on private networks than on the public Internet. What Is Meant by Next-Generation Network? The term next-generation network is used throughout this book with a very specific meaning. The decreasing cost of bandwidth, combined with the availability of low-cost and powerful chip technology, favorably highlights the economies of statistical multiplex- ing and packet switching, as long as latencies and loss can be controlled. From that standpoint, next-generation networks embody two fundamental concepts. First, a next- generation network is a high-speed packet-based network capable of transporting and routing a multitude of services, including voice, data, video, and multimedia, while sup- porting QoS. Second, a next-generation network is a common platform for applications and services that the customer can access across the entire network as well as outside the network. Converging Networks: Next-Generation Networks Networks are evolving so that they can address the growing demand for QoS. The two different infrastructures-circuit switching and packet switching-are not try- ing to replace each other. Instead, they are converging. This marriage is required Chapter 3 Establishing Communications Channels between the existing legacy environment (the circuit-switched network) and the new and unique IP marketplace (the packet-switched network). To address this convergence, a numbe