Quality of Service
Quality of Service |
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The RSVP service invokes traffic control on behalf of an application when QoS is requested. Traffic control refers to a collection of mechanisms that control and police a specific data flow once a QoS reservation has been established. Traffic control is used to segregate the traffic into the appropriate service classes, and regulate its delivery to the network. Figure 9.3 illustrates the traffic control components.
Figure 9.3 Traffic Control Components
A key element of traffic control is establishing the service parameters for a sequence of packets (known as flowspec) and then treating all member packets as a single flow. Traffic control uses information from the flowspec to create a flow with defined QoS parameters, and then creates filters to direct selected packets into this flow (known as filterspec).
Traffic control works with the QoS Admission Control Service and RSVP to meet the service level and priority required by the bandwidth request. Traffic control is also available in certain cases by using certain tools for subnet clients that are not QoS-aware, and controls data flow through network devices that are not RSVP-compliant by marking packets for 802.1p (layer 2 devices) or Differentiated Class of Service (layer 3 devices).
Traffic Control API (TC API) The TC API is a programmatic interface to the traffic control components that regulate network traffic on a host. The TC API allows the aggregation of traffic from a number of sources (on the same sending host) into a single traffic control flow. For example, all traffic to destination net 1.2.3.0 can be placed on the same flow, regardless of source address port and destination port. By comparison, the Generic QoS API limits the use of a traffic control flow to traffic from a single "conversation" only (a conversation is defined by source and destination address and port).
The TC API also works with GQoS to enable third-party traffic management applications that might request QoS on behalf of applications that are unable to do so on their own, or in situations where a system administrator wants to better control the QoS provided to applications. For more information about using the Traffic Control API, see the Software Development Kit link on the Web Resources page at http://windows.microsoft.com/windows2000/reskit/webresources.
