Quality of Service
Quality of Service |
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IP telephony provides an excellent example of the need for QoS admission control. When a user makes an IP telephone call to another user, the success of the communication relies on available priority bandwidth. Any new IP telephony sessions have the potential to degrade the quality of the first call that is still in progress, since these calls must share the same bandwidth. To guarantee QoS and successful throughput of the original call, admission control is needed to protect network resources.
When admission control is implemented, new calls are not permitted unless there is bandwidth available in the appropriate service class, and policy checking is used to verify who has access to high-priority bandwidth and on what subnet. For example, a user can have rights to request video from a local multimedia server, but might be restricted from requesting any video if the traffic must traverse a backbone network and exceed the limits for that backbone.
QoS Admission Control Service (QoS ACS) is a Windows 2000 component for managing network resources on a shared network segment (subnet). The QoS ACS provides a control point for bandwidth requests from the servers so that requests do not flood the subnet simultaneously. It is not required to implement the QoS ACS on every subnet; the highest benefit is realized from implementing the QoS ACS on congested segments.
As shown in Figure 9.8, the QoS ACS exerts its authority by placing itself within the RSVP message path, intercepting PATH and RESV messages, and passing the user information to the Local Policy Module (LPM) for authentication and policy lookup.
Figure 9.8 QoS Admission Control Service
The QoS ACS simplifies subnet administration by implementing:
