Asynchronous Transfer Mode

Introduction to ATM

Asynchronous Transfer Mode (ATM) describes several related, standards-based technologies that provide high-speed communication over a broad range of media. The International Telecommunication Union (ITU-T) defines ATM as "a high-speed, connection-oriented multiplexing and switching method specified in international standards utilizing fixed-length cells to support multiple types of traffic." Before you can decide whether to deploy ATM in your network, you need to understand how it integrates with current networking environments and how it functions in new networking environments.

Asynchronous Transfer Mode (ATM) is a wide array of services and concepts. At this time, ATM technologies are used selectively in local and wide area networks. Some networks have been completely transformed into native ATM networks, with software, end-station hardware, and network fabric all made up of ATM devices and drivers. In other networks, ATM is used only in the network backbone, shuttling data from one local area network (LAN) to another. In some instances, ATM is deployed in small pockets intermixed with standard LAN components and other networking technologies.

ATM is continually evolving. In some cases, its usefulness is judged by how well it emulates legacy networks; that is, how it compares with traditional LAN technologies such as Ethernet and Token Ring. In other cases, ATM provides so many clear advantages in terms of speed, manageability, and accuracy that it has quickly been recognized as the only viable solution.

To clarify ATM and to define the terms and concepts that are essential to any understanding of ATM, this chapter begins with an overview of ATM and its related technologies. It then describes how ATM is supported and integrated into current networks. The final section includes details on Microsoft Windows 2000 ATM support, how the support is achieved, and how you can maximize the new, native ATM services provided in Windows 2000.

The most important features of Windows 2000 ATM support are easy to list: it provides native support of LAN emulation, IP over ATM, TAPI, Direct Streaming, and other services. Each of these is further detailed in "Windows 2000 ATM Services" later in this chapter.