Chapter One

In the past, voice and data networks had been kept separate. Legacy network technologies simply could not meet the diverse performance requirements of both voice and data. Advances in networking technology, including fast Ethernet, wire-speed switching, and Policy-Based Quality of Service (QoS) management, have made it possible to build converged voice and data networks. Converged networks enable a new generation of integrated voice/data applications. For example, with converged networks, users of web-based e-commerce applications can view product information while talking with customer service agents in a call center, through a single network connection. The focus of most converged network strategies is Voice over IP (VoIP). VoIP refers to the transmission of telephone conversations over a packet-switched IP network. This IP network could be as small as a single subnet, private LAN, or as large as the public Internet. With VoIP on the LAN, telephone conversations are converted to a stream of IP packets and sent over an Ethernet network. This network is usually restricted to a building or campus. As VoIP technology matures, new conversion methods may emerge. Regardless of the method that is used to convert VoIP traffic for LANs, VoIP traffic will always traverse the LAN as a stream of IP packets. One of the key challenges in implementing VoIP is to design and build an IP-based network that meets QoS requirements and is comparable in performance to conventional circuit-switched telephone networks. The high latency forwarding and best-effort delivery provided by traditional software-based routers i