This document describes the configuration needed when call flow includes Integrated Service Router (ISR) 4431 as the gateway and the Music On Hold (MOH) fails with silence for the held party.
Cisco recommends that you have knowledge of:
Cisco Unified Communications Manager (CUCM)
The information in this document is based on these software versions:
CUCM versions 9.x and above
ISR4431 with IOS XE software
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure you understand the potential impact of any command.
Multicast MOH is configured on CUCM and ISR4431 is configured as H.323 gateway. When external callers are placed on hold, they do not hear music but instead hear silence.
Step 1. Enable the H.323 debugs on the gateway to be logged to the buffer as shown below.
config t no logging console no logging monitor no logging rate-limit no logging queue-limit logging buffered 2000000 debug exit debug voip ccapi inout debug h225 asn1 debug h245 asn1 debug isdn q931
Step 2. Run the command clear log to clear the log. Step 3. Run the command show log to confirm that the buffer is cleared. Step 4. Place a test call and when the call is placed on hold, check if the gateway receives H.245 OpenLogicalChannelAck message with IP set to “network '00000000'H”
CUCM sends OpenLogicalChannelAck with a fake IP address, either all zeros (as shown above) or <CUCM_ip_address> as a place-holder for MOH
This is the default behavior of sending media simplex streaming
If there is ISR 4431 in the call flow, whether or not it is one-way or two-way direction, CUCM needs to let the gateway know the MOH IP address and port to avoid a malicious attack
ISR Generation 2 (G2) platforms (e.g. 2900 and 3900) never check the source IP address and port for incoming Real-time Transport Protocol (RTP) packets. However ISR 4431 is a Generation 3 (G3) platform which checks incoming RTP packets against the media IP address/port determined in the signaling
If they do not match, ISR G3 drops the packets and this results in silence when call is placed on hold
Step 6. Thus to avoid failure with MOH, use the workaround below on CUCM to enable duplex streaming for the MOH
Log in to Cisco Unified CM Administration page
Select System > Service Parameters
Select Server dropdown and choose the Publisher node
Select Service dropdown and choose Cisco CallManager (Active)
Click on the Advanced button
Locate the Clusterwide Parameters (Service) section
Duplex Streaming Enabled: Default is False (change to True) and click Save
Note: There is no requirement to restart any service after above configuration change and has no business impact so can be done in production hours.