Admission Control Service

[This is preliminary documentation and subject to change.]

Admission Control Service (ACS), is a GQOS component that regulates subnet usage for QOS-enabled applications. The ACS exerts its authority over QOS-aware applications or clients by placing itself within the RSVP message path. With this placement, ACS effectively intercepts RSVP PATH and RESV messages and passes the messages' user information down to Local Policy Modules (LPMs) for authentication.

ACS regulation is based on available network resources and on administratively configurable information on users, applications, or group policy. ACS is implemented as a Windows NT service on a server running Windows NT.

Local Policy Modules (LPMs) fall within the fold of ACS functionality, and can be considered an integral part of the ACS. With the default LPM, user information is compared with Windows NT Active Directory policy information for authentication.

Another ACS component, the Policy Control Module (PCM), actually mediates the interaction between the ACS and LPMs. If there are multiple residential LPMs, the PCM will send user information to each LPM and gather all responses, then perform logical checks on the information, aggregate it, and return one response to the ACS.

If network resources are available and if authentication succeeds, the RSVP message and its policy information is sent to the next (or previous, depending on whether it is a PATH or RESV message) hop. In this way, ACS acts as the logical gatekeeper for RSVP message propagation across the network: No further RSVP processing will occur (since the RSVP won't be passed to the next appropriate hop), outside of an RSVP error message in either of the following cases:

• If local segment resources aren't available to provide the requested level of QOS (the SBM functionality of the ACS).
• If the sender or receiver doesn't have appropriate policy permission to transmit data at the requested rate.

This provides twofold service. It keeps unnecessary traffic from traversing the network by keeping lame-duck RSVP messages from running across the network, and it preserves processing resources for routers and WAN Network Interface Cards (WANICs) since they will not have to handle such RSVP messages. Note that any node that declines requests based on policy failure, however, will return and RSVP error message to the sender, indicating such failure.

Though ACS is a GQOS component, its services include other GQOS components, such as the Subnet Bandwidth Manager (SBM) and its LPM interface.