MGCP Gateway Fallback Configuration Example

When you are deploying MGCP in branch office and the WAN connection between the MGCP gateway and UCM is broken, you can enable fallback on IOS gateway and route call based on your H.323 configuration.

These are the commands that you need to configure on your MGCP gateway.

R1(config)#ccm-manager fallback-mgcp

R1(config)#application

R1(config-app)#global

R1(config-app-global)#service alternate Default

Also configure the necessary incoming and outgoing voip and pots dial-peer as well as SRST configuration to handle the fallback situation.

MGCP Signaling QoS marking

According to show mgcp, the default marking for MGCP signaling DSCP marking is AF31 (26):

MGCP media (RTP) dscp: ef, MGCP signaling dscp: af31

It can be override with the command:  mgcp ip qos dscp cs3 signaling

MGCP media (RTP) dscp: ef, MGCP signaling dscp: cs3

As a result the signaling is now marked as CS3 (24) instead of AF31 (26)

Basic MGCP router configuration using ccm-manager config server command

After configuring UCM MGCP configuration, on router you can config the MGCP feature with ease.  There is a feature called "ccm-manager config server" which configs the MGCP gateway automatically, by pulling configuration file from UCM as well as automatically config the router controller, voice-port and serial interfaces.  The basic settings that you need are as follows:

mgcp bind control source-interface gi0/0
mgcp bind media source-interface gi0/0
ccm-manager config server 192.168.20.2 192.168.20.1 ! UCM IP addresses, you can specify sub as primary and pub as backup
ccm-manager config

Then you can see the console messages showing the ISDN interface and other MGCP features are configured automatically.

Do a "show ccm-manager" and "show isdn status" to verify if it is configured properly.  If not, check out this post:
http://pandaeatsbamboo.blogspot.com/2012/02/isdn-shows-teiassigned-status-on-mgcp.html

If you make any changes that is different from the UCM configuration (e.g. config a partial T1 instead of using all channels), remember to no ccm-manager config server otherwise your configuration will be override after reloading the router

ISDN shows TEI_ASSIGNED status on MGCP gateway

My environment:  IOS 12.4(23)T3 advanced enterprise, 2821

When I try to config the MGCP using the ccm-manager config server, in "show ccm-manager" it shows the gateway is registered to UCM successfully:

Priority        Status                   Host

============================================================

Primary         Registered               192.168.20.2

First Backup    Backup Ready             192.168.20.1

Second Backup   None                     

However when I do "show isdn status", the Layer 2 status shows:

State = TEI_ASSIGNED

A router reload solved the problem, you should see

State = MULTIPLE_FRAME_ESTABLISHED

in "show isdn status" Layer 2 status.

Quick Note on H323 and MGCP call preservation

A quick summary on H323 and MGCP gateway call preservation behavior when it works with UCM:

MGCP (primary UCM dies)

PSTN <-- MGCP GW --> UCM <--> Phone

- enabled by default

- UCM dies, call preserved

- Call continues over the gateway

- supplementary services will not work

- new calls to MGCP gateway will not work until MGCP gateway re-registers with the backup UCM

H323 (primary UCM dies)

PSTN <-- H323 GW --> UCM <--> Phone

- Default has no call preservation

- configure with "call preserve" command

- will immediately begin to use backup UCM for supplementary service, outbound and inbound call routing

Branch voice gateway (WAN link down)

- SRST kicks in

- If MGCP, then MGCP fallback - fallback to H323 / SIP processing

- MGCP - Call drop immediately at the branch router

- H323 is recommended for branch router - call preservation feature after IOS 12.4(9T)

Call preservation is configured in the gateway with the following command syntax:

Router(config)#voice service voip
Router(conf-voi-serv)#h323
Router(conf-serv-h323)#call preserve

MGCP fallback is configured with the following command syntax:

Router(config)#ccm-manager fallback-mgcp
Router(config)#application
Router(config-app)#global

Router(config-app-global)#service alternate Default

Configuring MGCP

A quick cheat sheet for MGCP configuration:-

3 components for MGCP
Call Agent: Control operation of gateway, usually CUCM
Endpoint: point of connection between packet network and trad phone network, usually analog lines or voice trunk lines (DS0)
Gateway: Translation between packet network and switched network, usually voice-enabled router

Configuring MGCP on Residential gateway
ccm-manager mgcp

! Call-agent is the CUCM address, at least one call-agent address is required
mgcp
mgcp call-agent 1.2.3.4

voice-port 1/0/0

voice-port 1/0/1

dial-peer voice 1 pots
application MGCPAPP
port 1/0/0

dial-peer voice 2 pots
application MGCPAPP
port 1/0/1

A destination pattern is not used because the relationship between the dial number and the port is maintained by the call agent.


Configuring MGCP on Trunk Gateway
ccm-manager mgcp

mgcp
mgcp call-agent 1.2.3.4

controller T1 1/0
frame esf
clock source internal
ds0-group 1 timeslots 1-24 type none service mgcp

controller T1 1/1
frame esf
clock source internal
ds0-group 1 timeslots 1-24 type none service mgcp

voice-port 1/0:1

voice-port 1/1:1

Instead of using application mgcpapp command in a dial peer, the service mgcp parameter is used in the ds0-group controller subcommand to identifies its the trunk endpoint with MGCP. As always, the call agent maintains the relationship between the endpoint and its address.

Monitoring and troubleshooting
show call active voice
show call history voice
show mgcp
show mgcp connection
show mgcp endpoint
show mgcp statistics
debug voip ccapi inout <- Useful as always
debug mgcp all