Configuring Technology Prefixes
To enable the gatekeeper to select the appropriate hop-off gateway, use the gw-typeprefix
command 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.
As an example, Example 8-14 and Figure 8-35 illustrate a sample technology prefix configuration,
with 99# being used as a voice gateway technology prefix and 1# being used
as a default technology prefix.
Example 8-14 Zone Prefix Configuration Example
Chapter 8: Configuring H.323 Gatekeepers 495
San Jose
Gatekeeper
SanJose2
SanJose1
Phone1-1
2001
Phone1-2
2002
WAN
GK1
GK1(config)#gatekeeper
GK1(config-gk)#zone local SanJose cisco.com 10.1.1.10
GK1(config-gk)#zone local Houston cisco.com
GK1(config-gk)#zone prefix SanJose 2... gw-priority 10 SanJose
GK1(config-gk)#zone prefix Houston 3... gw-priority 10 Houston
GK1(config-gk)#gw-type-prefix 99#* gw ipaddr 192.168.1.1 1720
GK1(config-gk)#gw-type-prefix 1#* default-technology
GK1(config-gk)#no shutdown
Figure 8-35 Configuring Technology Prefixes
As an additional example, voice gateways might register with a technology prefix of 1#,
and H.320 gateways might register with a technology prefix of 2#. If several gateways of
the same type exist, 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.
Callers will need to know the technology prefixes that are defined and the type of device
they are trying to reach. This enables them to prepend the appropriate technology prefix
to the destination address for the type of gateway needed to reach the destination.
If the callers know the type of device they are trying to reach, they can include the technology
prefix in the destination address to indicate the type of gateway to use to get to
the destination. For example, if a caller knows that address 2125551111 belongs to a regular
telephone, the destination address of 99#2125551111 can be used, where 99# indicates
the address should be resolved by a voice gateway. When the voice gateway
receives the call for 99#2125551111, it strips off the technology prefix and bridges the
next leg of the call to the telephone at 2125551111.
Additionally, when you use the gw-type-prefix command, you can define a specific
gateway-type prefix as the default gateway type to be used for addresses that cannot be
resolved. This 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, you can configure the
gatekeeper 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 this command is entered:
GK1(config-gk)#gw-type-prefix 1#* default-technology
496 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
San Jose
Gatekeeper
Houston
(H.323)
SanJose
(H.323)
Houston
Phone2-1
3001
Phone2-2
3002
Phone1-1
2001
Phone1-2
2002
WAN
GK1
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 the call
hops off locally. However, if it knows the San Jose gatekeeper handles the 212 area code,
it can send a location request for 2125551111 to that gatekeeper. This requires the San
Jose gatekeeper also be configured with some default gateway-type prefix and its voice
gateways be registered with that prefix type.
Chapter 8: Configuring H.323 Gatekeepers 497
Note You must use consistent technology prefixes throughout a gatekeeper deployment
and have a consistent dial plan mapped out prior to implementation.