Multicasting

Chapter 9

Multicasting

Multicasting technology (or point-to-multipoint as it's sometimes called) allows data to be sent from one group member and then replicated to many others without creating a network traffic nightmare. This technology was developed as an alternative to broadcasting, which can negatively impact network bandwidth if used extensively. Multicast data is replicated to a network only if processes running on workstations in that network are interested in that data. Not all protocols support the notion of multicasting—on Windows platforms, only two protocols are multicast capable: IP and ATM. IP multicasting includes both IPv4 and IPv6. In addition, there are different types of IP multicasting. For example, Windows XP supports source multicasting for IPv4 as well as a reliable multicast provider that uses IP multicasting but adds reliability and session-oriented semantics. This chapter presents the information necessary to understand multicasting in general as well as how multicasting applies specifically to these protocols.

First, we will cover the basic semantics of multipoint networking, which includes the various possible types of multicasting as well as basic characteristics of IP and ATM multicasting. Then we will present the specifics of IP and ATM in their own sections. In each section, we will discuss how the Winsock API is used to access each protocol's multicast features.

All Windows platforms support one or more multicasting protocols. IPv4 multicasting is available on all Windows platforms (Windows CE requires version 2.1 or greater). IPv6 multicasting is available in Windows XP as well as in Windows 2000 with the IPv6 technology preview and in Windows NT 4.0 with the Microsoft Research IPv6 stack. Reliable multicasting is available in Windows XP if the Microsoft Message Queue (MSMQ) component is installed. Finally, native ATM multicasting is available in Windows 98, Windows Me, Windows 2000, and Windows XP.