Chapter 12 -- Generic Quality of Service

Chapter 12

With the wide variety of multimedia applications available today, as well as the popularity of the Internet, many networks are becoming saturated with the traffic of these bandwidth-hungry applications. This is especially a problem on shared media networks—such as Ethernet—because all traffic is treated equally and a single application can flood the network. Quality of Service (QOS) is a set of components that allows the differentiation and preferential treatment of data on the network. A QOS-enabled network can be configured to offer programmers the following capabilities:

• Prevent nonadaptive protocols (such as UDP) from abusing network resources
• Partition resources between "best-effort" traffic and higher-priority or lower-priority traffic
• Reserve resources for entitled users
• Prioritize access to resources based on the user

Generic Quality of Service (GQOS) is Microsoft's implementation of QOS. Currently Microsoft supplies a QOS-enabled TCP/IP and UDP/IP provider that is available on Windows 98 and Windows 2000. Note that the ATM protocol is capable of QOS because it is available natively in ATM.

This chapter covers QOS and how it is implemented on Win32 platforms. We will begin with a discussion of the various components that need to be in place to allow preferential treatment of network traffic. Then we'll examine how the Winsock interface exposes the ability to write a network application that can take advantage of these components for time- and bandwidth-critical applications. The majority of this chapter is dedicated to QOS on IP networks. At the end of this chapter, we will discuss QOS on ATM networks, which is slightly different from QOS on IP networks.

NOTE

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Throughout the chapter, we will refer to Quality of Service as QOS. You can assume that we are discussing Microsoft's implementation of QOS.