Adding Trunk Gateway to CUCM 8.0 as H323 or MGCP, Differences and Configurations

To add a Trunk gateway to CUCM we can use one of the two Protocols H323 or MGCP, the decision of which protocol to use depends on the required features. MGCP Protocol will allow you to simplify your configuration and your dialplan as you will see you only need to commands to be entered at the gateway and then you can completely control the gateway and your dialplan from CUCM, Moreover with MGCP you can use Q.931 backhaul where the gateway is still responsible for the termination of the Layer 2 signaling (Q.921 link access procedure over the D channel [LAP-D]). The gateway will not bring up the D channel unless it can communicate with CUCM to backhaul the Q.931 messages contained in the D channel.
A Q.931 backhaul channel is a logical TCP connection between CUCM and Cisco MGCP gateways. Q.931 backhaul forwards the Q.931 signaling traffic from an ISDN interface on a gateway over TCP port 2727 to a CUCM configured as an MGCP call agent. one disadvantage of MGCP is when you have analog Trunks, MGCP doesn’t support CLID. On the other Hand H323 will give you more Control on the dialplan as you can configure your dialpeers and Digit manipulation on the gateway itself. Cisco Always recommend using MGCP due to its simplicity Unless special features are required like CLID on FXO trunks, So to summarize the main three differences between MGCP and H323 are as follows:
MGCP vs H323

MGCP vs H323

MGCP Gateway Configuration(CUCM):
To add the gateway to CUCM follow below instructions:

- From CUCM Administration, choose Device > Gateway.
- Click the Add New button. The Add a New Gateway window will open.
- From the Gateway Type drop-down list, choose the appropriate MGCP gateway (2801, 2811, etc) and click next.
- Choose MGCP from the Protocol drop-down menu and click Next.
- Enter the hostname or fully qualified domain name of the gateway in the Domain Name field, the name has to match the hostname or The hostname and domain name (fully qualified domain name) of the Cisco IOS router.
- Enter a description for the gateway.
- Select a CUCM group.
- Configure the IDSN switch type.
- Click Save. Reset the gateway for the configuration changes to apply.
- Locate the Configured Slots, VICs, and Endpoints section, and select the voice hardware module placed in the slot.
- Click Save. The subunits (voice interface cards slots) of the selected voice module will display.
- For each subunit (voice interface cards slot), select the subunit. (show diag at th gateway will list modules and interface cards that the gateway is equipped with)
- Click Save. The endpoints of the selected voice interface card will display.

To configure an MGCP endpoint, follow these steps:

- Click the endpoint identifier.
- Select the device protocol or signaling for the endpoint. T1 and E1 interfaces support channel associated signaling (CAS) or command channel signaling (CCS) via ISDN PRI. Analog interfaces support ground-start and loop-start signaling. Select the protocol that should be used on the endpoint and click Next.
- Enter a description for the endpoint
- Select the device pool that should be used by this endpoint.
- Click Save. Reset the gateway for configuration changes to be committed to the gateway.

MGCP Gateway Configuration:

To configure the gateway as an MGCP gateway, there is only two commands needed on the gateway as follows:

ccm-manager config server (CUCM IP address)
ccm-manager config

MGCP Gateway Registration Verification:

use show ccm-manager at the gateway to verify MGCP Gateway registration to CUCM was successful
use show mgcp endpoints
at the gateway to verify MGCP Endpoints have registered

H323 Gateway Configuration(CUCM):

To add the gateway to CUCM follow below instructions:
- From CUCM Administration, choose Device > Gateway.
- Click the Add New button. The Add a New Gateway window will open.
- From the Gateway Type drop-down list, choose H323 Gateway (you can’t select the router type) and click next.
- Enter the IP address or name (must be resolved by DNS) and Enter a description for the gateway (this is optional).
- Select the Device pool from the drop-down list then save.
- verify the inbound and outbound calls related parameters.
H323 Gateway will never register with CUCM but the gateway IP address will show up after communication occurs, the status of the gateway will always show Unknown.
H323 Gateway Configuration:

To configure the gateway as an MGCP gateway, there is only two commands needed on the gateway as follows:
Interface (Int ID)
IP address ………IP address…… …………….Subnet mask…………
H323-gateway voip Interface
H323-gateway voip bind srcaddr …..IP address……..
If you have redundant links that can reach CUCM then you need to create Loopback interface and Bind the loopback interface for H323 Communications.
Configure Cisco IOS Call Routing with single CUCM or Redundant CUCM:

To configure your H323 gateway to forward calls to CUCM, you need to tell the gateway which called number should be routed to which CUCM using a voip dialpeer as follows:
dial-peer voice tag
voip destination-pattern …… (Called Number that should be routed to CUCM which is your Extension number on CUCM)
session target IPV4:……………. (IP address of your primary CUCM)
If you have redundant call managers then you need to add a second dial-peer with the IP address of the secondary CUCM and a Preference of 1. and then to adjust the tcp establish timeout to minimize the time gateway takes to reroute calls to secondary CUCM when the primary fails, the complete configuration in this case would be:
Voice Class H323 tag
H225 timeout tcp establish Seconds(recommended 2 Seconds)
H225 timeout setup Seconds (recommended 2 Seconds)
dial-peer voice tag voip
Voice-Class H323 tag
destination-pattern 2…
session target IPV4:……………. (IP address of your primary CUCM)
dial-peer voice tag voip
Voice-Class H323 tag
destination-pattern 2…
session target IPV4:……………. (IP address of your Secondary CUCM)
Preference 1
Below is the difference between the two timeout commands
H225 timeout tcp establish: If the H323 gateway can’t establish a tcp Connection with IP address defined in the dial-peer with preference 0 within the specified time then the next dial-peer will be used. therefore this command is mandatory for dial-peer with preference 0 but optional for the other one.
H225 timeout setup: This command will define the time that the gateway will wait for a response from CUCM when trying to establish a tcp connection, if the CUCM didn’t respond within the defined time the next dial-peer will be used.
H323 Gateway Call Survivability

By default when the signalling between the H323 Gateway and CUCM is lost, the RTP stream of active calls will be disconnected after H225 Keepalive timeout.To maintain your TDM-to-IP Calls for Trunk Gateways use the below commands:
Voice Service Voip
H323
no H225 timeout Keepalive
To maintain your IP-to-IP Calls for IP Trunk Gateways (CUBE) use the below commands:
Voice Service Voip
allow-connections H323 to H323
Voice Class H323 tag (this is the same Voice class that you defined for redundant CUCM above)
Call Preserve

And don’t forget that you need to associate this gateway to route pattern on CUCM if you would like your outgoing calls to be routed through this gateway, I think my next Post would be on How to add SIP Gateway to CUCM.

About Qasim

Qasim Alhammad has written 48 post in this blog.

IP Telephony Engineer and blogger. Interested in IP Telephony, SEO, Social Media, Web traffic, Blogging tips, internet marketing and making money online. Founder and owner of MsocialH online Forum, blogging for ICCIEV IP Telephony blog and AliensMoney blogs.

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