The Windows QoS implementation consists of several components, as shown in Figure 7-44. First, the QoS Client Side Extension (%SystemRoot%\System32\Gptext.dll) notifies the Group Policy client and the QoS Inspection Module that QoS settings have changed. Next, the QoS Inspection Module (Enterprise Quality of Service, eQoS), which is a WFP packet-inspection component implemented in the TCP/IP driver that reacts to policy changes, retrieves the updated policy and works with the transport layer and QoS Packet Scheduler to mark traffic that matches the policy. Finally, the QoS Packet Scheduler, or Pacer (%SystemRoot%\System32\Drivers\Pacer.sys), provides the NDIS lightweight filter functionality, such as throttling and setting the DSCP value, to control packet scheduling based on the QoS policies. Pacer also provides the GQoS (Generic QoS) and TC (Traffic Control) API support for legacy Windows applications that used these mechanisms.
In addition to the systemwide, policy-based QoS support provided by the QoS architecture, Windows enables specific classes of socket-based applications to have individual and specific control of QoS behavior through an API called the Quality Windows Audio/Video Experience, or qWAVE. Network-based multimedia applications, such as Voice over IP (VoIP), can use the qWAVE API to query information on real-time network bandwidth and adapt to changing network conditions, as well as to prioritize packets to efficiently use the available bandwidth. qWAVE also takes advantage of the topology protocols described earlier to dynamically determine if the current network devices will support the required bandwidth for a video stream, for example. It can notify applications of diminishing bandwidth, at which point the multimedia application is expected to reduce the stream quality, for example.
qWAVE is implemented in the QoS2 (%SystemRoot%\System32\Qwave.dll) API library and provides four main components:
Admission control, which determines, when a new network multimedia stream is started, if the current network can support the sustained bandwidth requested.
Caching, which allows the detailed admission control checks to be bypassed if similar usage patterns occurred in the past and the calculation result was already cached.
Monitoring and probing, which keep track of available bandwidth and notify applications during low-bandwidth or high-latency situations.
Traffic tagging and shaping, which uses the 802.11p and DSCP technologies mentioned earlier to tag packets with the appropriate priority to ensure timely delivery.
Figure 7-45 shows the general overview of the qWAVE architecture:
Binding
The final piece in the Windows networking architecture puzzle is the way in which the components at the various layers—networking API layer, transport driver layer, NDIS driver layer—locate one another. The name of the process that connects the layers is
When you install a networking component, you must supply an INF file for the component. (INF files are described in Chapter 8 in Part 2.) This file includes directions that setup API routines must follow to install and configure the component, including binding dependencies or binding relationships. A developer can specify binding dependencies for a proprietary component so that the Service Control Manager (the Service Control Manager is described in Chapter 4) will not only load the component in the correct order but will load the component only if other dependent components are present on the system. Binding relationships, which the bind engine determines with the aid of additional information in a component’s INF file, establish connections between components at the various layers. The connections specify which components a network component on one layer can use on the layer beneath it.
Вильям Л Саймон , Вильям Саймон , Наталья Владимировна Макеева , Нора Робертс , Юрий Викторович Щербатых
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