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DQOS Exam Certification Guide - Cisco press.pdf
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584 Chapter 8: Call Admission Control and QoS Signaling

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

Evaluation Criteria




Topology awareness




Guarantees QoS for duration of call




Postdial delay

Only for first call that initiates probe



Messaging network overhead

Periodic SAA probes



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:

Resource Availability Indication

CallManager Locations

Gatekeeper Zone Bandwidth

Resource Reservation Protocol

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.