Configuring H.323 Gatekeepers and Proxies

H.323 Gatekeeper Features

Interzone Routing Using E.164 Addresses

Interzone routing may be configured using E.164 addresses.

Two types of address destinations are used in H.323 calls. The destination can be specified using either an H.323-ID address (a character string) or an E.164 address (a string that contains telephone keypad characters). The way interzone calls are routed depends on the type of address being used.

When using H.323-ID addresses, interzone routing is handled through the use of domain names. For example, to resolve the domain name bob@cisco.com, the source endpoint gatekeeper finds the gatekeeper for cisco.com and sends it the location request for the target address bob@cisco.com. The destination gatekeeper looks in its registration database, sees bob registered, and returns the appropriate IP address to get to bob.

When using E.164 addresses, call routing is handled through zone prefixes and gateway-type prefixes, also referred to as technology prefixes. The zone prefixes, which are typically area codes, serve the same purpose as domain names in H.323-ID address routing. Unlike domain names, however, more than one zone prefix can be assigned to one gatekeeper, but the same prefix cannot be shared by more than one gatekeeper.

Use the zone prefix command to define gatekeeper responsibilities for area codes. The command can also be used to tell the gatekeeper which prefixes are in its own zones and which remote gatekeepers are responsible for other prefixes.

Note Area codes are used as an example in this section, but a zone prefix need not be an area code. It can be a country code, an area code plus local exchange (NPA-NXX), or any other logical hierarchical partition.

The following sample command shows how to configure a gatekeeper with the knowledge that zone prefix 212....... (that is, any address beginning with area code 212 and followed by seven arbitrary digits)

is handled by gatekeeper gk-ny:my-gatekeeper(config-gk)#zone prefix gk-ny 212.......

When my-gatekeeper is asked to admit a call to destination address 2125551111, it knows to send the location request to gk-ny.

However, once the query gets to gk-ny, gk-ny still needs to resolve the address so that the call can be sent to its final destination. There could be an H.323 endpoint that has registered with gk-ny with that E.164 address, in which case gk-ny would return the IP address for that endpoint. However, it is more likely that the E.164 address belongs to a non-H.323 device, such as a telephone or an H.320 terminal.

Because non-H.323 devices do not register with gatekeepers, gk-ny has no knowledge of which device the address belongs to or which type of device it is, so the gatekeeper cannot decide which gateway should be used for the hop off to the non-H.323 device. (The term hop off refers to the point at which the call leaves the H.323 network and is destined for a non-H.323 device.)

Note The number of zone prefixes defined for a directory gatekeeper that is dedicated to forwarding LRQs, and not for handling local registrations and calls, should not exceed 10,000; 4 MB of memory must be dedicated to describing zones and zone prefixes to support this maximum number of zone prefixes. The number of zone prefixes defined for a gatekeeper that handles local registrations and calls should not exceed 2000.

Cisco IOS Voice, Video, and Fax Configuration Guide

VC-294

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Cisco Systems VC-289 manual Interzone Routing Using E.164 Addresses, VC-294
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VC-289 specifications

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