Refer to the exhibits.

The gateway CSS for inbound calls is configured using internal. CSS, which contains all the
directory number partitions for the phones. When a PSTN call that is destined for extension 2001
arrives at the MGCP gateway, the call falls. Use the debug and configuration information in the
exhibits to determine what might be causing this issue?

A.
The MGCP gateway L3 timers need to be increased.

B.
The backhaul link is not open.

C.
The gateway is using partial PRI, which is not supported in MGCP mode.

D.
Incoming dial-peer configuration is needed.

E.
The hostname for the gateway does not match the configuration in Cisco Unified
Communications Manager.

Explanation:
On the picture „show ccm-manager“ you can recognize that the backhaul link is not open. You can
also see that the „isdn bind-l3 ccm-manager“ is missing on controller. That is the cause of issue.
The answer should therefore be “The MGCP gateway L3 timers need to be
increased”?http://www.cisco.com/en/US/tech/tk1077/technologies_configuration_example09186a0
0801ad22f.shtml