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Figure 3-5 illustrates the relationship between CUCM and an H.323 gateway.
H.323 gateway implementation requires configuration of CUCM and the Cisco IOS
gateway. In CUCM, the important configuration steps are as follows:
Step 1 Create the gateway, and specify its IP address.
Step 2 Create a route group, and put the gateway into it.
Step 3 Create a route list, and put the route group into it.
Step 4 Create one or more route patterns pointing to the route list.
Chapter 3: Implementing Multisite Connections
Figure 3-5 H.323 Gateway Implementation Overview
NOTE The number of settings available in CUCM for an H.323 gateway is substantially
less than those for an MGCP gateway. This is intentional by design, because MGCP is a
client/server protocol and CUCM must contain all gateway settings. In contrast, H.323
is a peer-to-peer protocol, and CUCM simply needs to know how to talk to the gateway.
The Cisco IOS gateway configuration consists of these steps:
Step 1 Configure the H.323 gateway, specifying its H.323 ID and the IP address
to use. This is done on any interface, but best practice for reliability is to
use a loopback interface. Ensure that you use the same IP address you
configured in CUCM for the H.323 gateway.
NOTE If the IP address configured in CUCM does not match the IP address used by the
gateway, CUCM considers the H.323 signaling messages to be sent from an invalid
(unknown) source and ignores them, unless promiscuous operation has been permitted.
(This service parameter can be configured in CUCM.)
Step 2 Configure one or more VoIP dial peers pointing to CUCM.
Step 3 Configure one or more dial peers pointing to the PSTN.
H.323 Gateway Implementation 63
Cisco IOS H.323 Gateway Configuration
Example 3-2 shows an IOS configuration for the H.323 gateway in the network topology,
illustrated in Figure 3-6.
Example 3-2 Cisco IOS H.323 Gateway Configuration
i n t e r f a c e LoopbackO
i p address 10.1.1.101 255.255.255.255
h323-gateway voip i n t e r f a ce
h323-gateway voip bind srcaddr 10.1.1.101
1
d i a l - p e e r voice 11 voip
d e s t i n a t i o n - p a t t e r n 5 1 1 5 5 5 . . ..
session t a r g e t i p v 4 : 1 0 . 1 . 1 .1
incoming called-number 9T
codec g711ulaw
1
d i a l - p e e r voice 21 pots
d e s t i n a t i o n - p a t t e r n 9T
d i r e c t - i n w a r d - d i a l
port 0/0/0:23
Figure 3-6 Cisco IOS H.323 Gateway Configuration
Chapter 3: Implementing Multisite Connections
NOTE The use of 9T in dial peer 21 shown in Example 3-2 is just an example. More
granular destination pattern configurations typically are used in production to allow
greater call control. Additional information on how to implement digit manipulation is
provided in the next chapter.
CUCM H.323 Gateway Configuration
Figure 3-7 shows an example of a CUCM H.323 gateway configuration.
To add an H.323 gateway to CUCM, choose Device > Gateway and click Add New. Then,
from the Gateway Type drop-down list, choose H.323 and click Next.
When configuring an H.323 gateway, be sure to first enable H.323 at one IP interface. If
multiple IP interfaces are present, it is recommended that you use a loopback interface.
Otherwise, if the interface that has been selected for H.323 is down, the H.323 application
will not work, even if other interfaces could be used to route the IP packets. In this example,
H.323 has been enabled on the loopback interface using the h323-gateway voip interface
and h323 gateway voip bind srcaddr IP address commands.
In contrast to MGCP gateways, in which the call agent takes care of call routing, H.323
gateways require local dial plan configuration. In the example, the H.323 gateway is
configured with a VoIP dial peer that routes calls placed to the gateway's PSTN number
511555.... toward CUCM. These are the calls that the gateway receives from the PSTN,
because 511555 1001-1003 is the direct inward dialing (DID) range of the PSTN interface
(port 0/0/0:23). In addition, the PSTN gateway is configured with a plain old telephone
service (POTS) dial peer that routes all calls starting with 9 to the PSTN using the ISDN
PRI (port 0/0/0:23).
Note that the configured digits of a destination pattern in a POTS dial peer are automatically
stripped, because POTS dial peers send only wildcard (variable) digits by default. Therefore,
the 9 is not sent to the PSTN. In the other direction, the gateway does not perform any digit
manipulation, because VoIP dial peers do not strip any digits by default. CUCM receives
H.323 call setup messages for calls that were received from the PSTN in full length (usually
ten digits). Because the internal directory numbers are four digits, either CUCM or the
H.323 gateway needs to be configured to strip the leading digits so that the remaining four
digits can be used to route the call to internal directory numbers.
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