For the last several chapters we have looked at the radio links, protocols, and security attributes of wireless LANs. Now it is time to address the other major technology that supports WLAN voice, Voice over IP (VoIP). Traditionally, organizations have built and maintained separate networks for their voice and data traffic, but we now have the network tools to build a single network that would combine both types of traffic and carry video as well. The underlying technology would be packet switching based on the concepts of IP routing.

The obvious advantage of this convergence would be cost savings. Rather than leasing separate equipment and facilities to support voice, video, and data requirements, an organization could invest in a single shared infrastructure. Should we elect to use it, the dynamic allocation capability of packet switching could reduce the total wide area network capacity leased from the carriers. Further, new additions to IP routing like Multi-Protocol Label Switching can provide preferred handling for voice and video packets, thereby ensuring better service quality for those time and loss sensitive applications.

To understand the challenges involved in carrying voice on an IP network, some background in TCP/IP is essential. We will introduce the overall concept of a layered model and the Open Systems Interconnection (OSI) reference model, and then examine in detail how those concepts apply to the TCP/IP protocol suite. In particular we will describe the functions of the Real-time Transport Protocol (RTP), the IP protocol for voice transport, and how Multi-Protocol...