Core Issue
If you check the Cisco CallManager trace, the Telco is sending full number (en bloc mode), while CiscoCallManager is sending back the SETUP_ACK, waiting for more number (overlap mode).
Cisco routers can receive an ISDN call in en bloc mode or overlap mode. When configured for en bloc, the setup message should contain all necessary addressing information to route the call. In overlap, the setup message does not contain the complete address. By default, H.323 is running on en Bloc mode but with Media Gateway Control Protocol (MGCP), it runs in verlap mode.
Resolution
To resolve this issue, turn off the Overlap Receiving Flag for PRI in Cisco CallManager by performing these steps:
- Open up the Cisco CallManager Administration.
- Go to Service > Service Parameters.
- Select Cisco CallManager from the Service pulldown menu.
- In the Service Parameters Configuration page, look for the name for Overlap Receiving Flag for PRI.
- Change the parameter from True to False.
- Click Update.
Note: The Overlap Receiving Flag for PRI parameter indicates whether overlap receiving is enabled for all PRI interfaces that use the PRI backhaul mechanism. Valid values are True (overlap receiving is supported) or False (overlap receiving is not supported). Default value is True.
To resolve this problem, upgrade the Cisco CallManager to version 3.3(4) or 4.0(2a). Refer to Voice Software.
For more information, refer to these documents:
Problem Type
Call control software (CallManager, CallManager Express, ICS7750, SRST, SS7 call agents)
Call connection (Connection quality: One-way audio, no busy tone, dropped calls, etc.)
Call Control
CallManager
Call Connection
Busy tone
Reorder tone
CallManager Features
Bad operational behavior, status,information, performance, delay or other CCM failure
Call routing
Failure Type
Nothing transmitted: Not sent or received, notification, alert or delivery, etc.
Cannot connect to server, disconnect, register, synchronize, communicate, etc.
Bad operational behavior
Frequency and Scope of Symptom
Occurs only on some calls
When Problem Occurs
After last digit is dialed
Call Topology and Direction
PSTN/PBX/gateway > IP network
Signaling Protocol
MGCP
TDM Signaling Type
Digital
PRI
T1
MGCP Features
MGCP gateway
CallManager Versions
CallManager 4.1
CallManager 3.0
CallManager 3.1
CallManager 3.2
CallManager 3.3
CallManager 4.0