Quality of Service
Quality of Service |
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Enterprise network administrators might be primarily concerned with providing QoS for mission-critical applications, such as Enterprise Resource Planning (ERP) applications, and secondarily concerned with providing QoS for multimedia applications.
As a result, Microsoft supports both quantitative and qualitative QoS in order to support ERP and other mission-critical applications that are qualitative in nature. Traditional RSVP signaling uses the IETF-defined Integrated Services (Intserv) model for expressing network resource requirements in a quantitative form. While this is suitable for multimedia applications such as IP telephony or video conferencing, it is not suitable for qualitative applications that cannot easily express resources required in the quantitative form required by Intserv.
Through extensions to RSVP signaling, Microsoft provides the necessary support for qualitative applications by enabling a new service type called the Qualitative Service Type (see "Traffic Control" in this chapter). Applications must be designed to include the requested service type in the basic QoS parameters. Applications must also be designed to create a policy element that includes the application and subapplication names. This policy element is compared against the policy database to determine which policy must be applied to that application traffic. All other QoS functionality is handled by the operating system. See the IETF-defined Internet Draft titled "Specification of the Qualitative Service Type" for detailed information about this service level.
The application and subapplication names are included in the signaling message with the service type. When this service type is requested, network devices interpret the request as a data flow that requires some special treatment, although the network devices do not know exactly what that treatment is. The network devices look up this application, the type of application subflow, and the requesting user in the policy database, and determine the best prioritization policy for this traffic. Therefore, the network devices do not actually allocate a specific quantity of resources to the application's traffic, but rather assign it to a particular Differentiated Class of Service. In addition, the network administrator must specify (using policy or registry settings) how to map data flows from different applications into a smaller set of aggregate service classes. This enables the prioritization of traffic from specific qualitative applications.