Generic Quality of Service

Chapter 10

Generic Quality of Service

With the 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. QOS is a set of components that allows the differentiation and preferential treatment of data on a network. A QOS-enabled network can be configured to offer programmers the following capabilities:

• Prevent non-adaptive 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/IPv4 and UDP/IPv4 provider that is available in Windows 98, Windows Me, Windows 2000, and Windows XP. However, in Windows XP, the IP QOS provider is scaled down and does not offer full GQOS functionality, as we will describe later in the chapter. Note that QOS is not available over IPv6 providers. Microsoft platforms also can access QOS using the ATM protocol because QOS functionality is available natively in ATM.

This chapter covers QOS and how it is implemented on Windows platforms. We will begin with a discussion of the components that need to be in place to allow preferential treatment of network traffic. Then we'll examine how the Winsock interface exposes the capability 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.

	Throughout the chapter, you can assume that when we refer to QOS, we are discussing Microsoft's implementation of it.