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Chapter 5 Dial Plan Architecture and Configuration

The Role of a Gatekeeper

5-22

Cisco IP Telephony Network Design Guide

78-11103-03

Figure 5-9 Using a Gatekeeper for Call Admission Control

If the WAN is unavailable in this scenario, the call cannot go through as dialed.

No automatic fallback is available because, once Cisco CallManager 1XXX is

informed that the call cannot be placed, no further mechanism exists for

intelligent digit manipulation. (For example, Cisco CallManager cannot

determine what area code and prefix to append to the originally dialed digits.) At

that point, the originating subscriber must attempt to establish the call via an

alternative route such as the PSTN.

If you wanted to simplify the dial plan and also provide fallback to the PSTN in

this scenario, use 10-digit dialing (or adhere to the national dial plan). For

example, under the North American Numbering Plan (NANP), a route pattern of

XXXXXXXXXX would direct calls to the gatekeeper (Anonymous Calls Device)

for address resolution. If the gatekeeper does not allow the call to go over the

WAN, then Cisco CallManager can add the prefix 91 to the dialed digits to reroute

the call through the PSTN.

IPIP

Cisco 3600 Cisco 3600

WAN

PSTN

"voice overflow"X1001 X2002

Cisco IOS Gatekeeper

Cisco

CallManager 1xxx

Cisco

CallManager 2xxx

"Call placed"

Call flow

H.323 RAS

signaling

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Cisco WS-X4604-GWY - VoIP Gateway Especificaciones Pagina 130