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Cisco IP Telephony Network Design Guide

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Chapter 6 Multisite WAN with Distributed Call Processing

Dial Plan Considerations

Considerations for Using a Gatekeeper

The following considerations apply when using gatekeeper-based call admission

control:

• The gatekeeper must be the Cisco IOS MCM. Recommended platforms are

the Cisco 2600, 3600, or 7200 with Cisco IOS Release 12.1(3)T or greater.

• When using two gatekeepers in a redundant fashion and the primary one fails,

the second gatekeeper becomes the primary with no knowledge of existing

calls. This poses the possibility that poor quality could result if the new

primary gatekeeper allows too many new calls in addition to existing calls of

which it is unaware. This is a short-term situation that resolves when existing

calls are terminated.

• Mobility of devices between sites is not possible unless a new number is

assigned to the device to ensure that it uses the local Cisco CallManager for

call processing.

Dial Plan Considerations

A new feature in Cisco CallManager Release 3.0(5) is the ability of the gatekeeper

to resolve the dial plan between Cisco CallManager clusters. In prior releases,

only Cisco CallManager could resolve the dial plan between clusters. With

Cisco CallManager Release 3.0(5), there are now three deployment models for

resolving the destination of intercluster calls:

• Cisco CallManager dial plan model (see Figure 6-9)

• Gatekeeper dial plan model (see Figure 6-10)

• Hybrid dial plan model

The Cisco CallManager dial plan model requires every Cisco CallManager

cluster to have an intercluster trunk and a route pattern to each of the other

clusters. The administrative overhead grows exponentially as the number of

clusters increases. In this model, the gatekeeper provides only call admission

control and not dial plan resolution. This model closely resembles the standard

model used today in traditional PBXs.

The gatekeeper dial plan model, even in the hybrid form, greatly reduces

configuration and administration overhead. In this model, each

Cisco CallManager has only one intercluster trunk, known as the

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Cisco WS-X4604-GWY - VoIP Gateway Especificaciones Pagina 145