584 Chapter 8: Call Admission Control and QoS Signaling

Table 8-12 PSTN Fallback CAC Evaluation Criteria (Continued)

Resource-Based CAC

There are two types of resource-based CAC mechanisms:

•Those that monitor the use of certain resources and calculate a value that affect the CAC decision

•Those that reserve resources for the call

The reservation mechanisms are the only ones that can attempt to guarantee QoS for the duration of the call. All other local, measurement-based and resource calculation-based CAC mechanisms just make a one-time decision prior to call setup, based on knowledge of network conditions at that time.

The following resources are of interest to voice calls:

•DS0 time slot on the originating and terminating TDM trunks

•Digital signal processor (DSP) resources on the originating and terminating gateways

•CPU use of the involved nodes, typically the gateways

•Memory use of the involved nodes, typically the gateways

The following sections focus on the following four resource-based CAC techniques:

Like the measurement-based CAC techniques, these techniques add visibility into the network itself in addition to the local information discussed in the previous sections.