Cisco Systems VC-289 manual VC-295, Call Scenario

Configuring H.323 Gatekeepers and Proxies

H.323 Gatekeeper Features

To enable the gatekeeper to select the appropriate hop-off gateway, use the gw-type-prefixcommand to configure technology or gateway-type prefixes. Select technology prefixes to denote different types or classes of gateways. The gateways are then configured to register with their gatekeepers using these technology prefixes.

For example, voice gateways might register with technology prefix 1#, and H.320 gateways might register with technology prefix 2#. If there are several gateways of the same type, configure them to register with the same prefix type. By having them register with the same prefix type, the gatekeeper treats the gateways as a pool out of which a random selection is made whenever a call for that prefix type arrives. If a gateway can serve more than one type of hop-off technology, it can register more than one prefix type with the gatekeeper.

Callers will need to know the technology prefixes that are defined. The callers will need to know the type of device they are trying to reach and will need to prepend the appropriate technology prefix to the destination address to indicate the type of gateway needed to reach the destination.

For example, callers might request 1#2125551111 if they know that address 2125551111 is for a telephone and that the technology prefix for voice gateways is 1#. The voice gateway is configured with a dial peer (using the dial-peercommand) so that when the gateway receives the call for 1#2125551111, it strips off the technology prefix 1# and bridges the next leg of the call to the telephone at 2125551111.

In cases in which the call scenario is as shown in Figure 57, voice-gw1 can be configured to prepend the voice technology prefix 1# so that the use of technology prefixes is completely transparent to the caller.

Figure 57	Call Scenario
PSTN		H.323 network	PSTN

Telephone voice-gw1 voice-gw2 Telephone

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Additionally, in using the gw-type-prefixcommand, a particular gateway-type prefix can be defined as the default gateway type to be used for addresses that cannot be resolved. It also forces a technology prefix to always hop off in a particular zone.

If the majority of calls hop off on a particular type of gateway, the gatekeeper can be configured to use that type of gateway as the default type so that callers no longer have to prepend a technology prefix on the address. For example, if voice gateways are mostly used in a network, and all voice gateways have been configured to register with technology prefix 1#, the gatekeeper can be configured to use 1# gateways as the default technology if the following command is entered:

my-gatekeeper(config-gk)#gw-type-prefix 1# default-technology

Now a caller no longer needs to prepend 1# to use a voice gateway. Any address that does not contain an explicit technology prefix will be routed to one of the voice gateways that registered with 1#.

With this default technology definition, a caller could ask the gatekeeper for admission to 2125551111. If the local gatekeeper does not recognize the zone prefix as belonging to any remote zone, it will route the call to one of its local (1#) voice gateways so that the call hops off locally. However, if it knows that gk-ny handles the 212 area code, it can send a location request for 2125551111 to gk-ny. This requires that gk-ny also be configured with some default gateway type prefix and that its voice gateways be registered with that prefix type.

Cisco IOS Voice, Video, and Fax Configuration Guide

VC-295