How do companies choose Hold Music


This document describes the configuration required when the call flow includes the Integrated Service Router (ISR) 4431 as a gateway and the music on hold (MOH) for the party on hold is silent.



Cisco recommends that you have knowledge of the following areas:

  • Cisco Unified Communications Manager (CUCM)
  • H.323 signaling

Components used

The information in this document is based on the following software versions:

  • CUCM versions 9.x and higher
  • ISR4431 with IOS XE software

The information in this document was produced by the devices in a specific laboratory environment. All devices used in this document started with an empty (standard) configuration. With your network up and running, make sure you understand the potential implications of a command.


Multicast music on hold is configured on the CUCM and the ISR4431 is configured as an H.323 gateway. When outside callers are put on hold, they will not hear music and instead hear silence.


Step 1: Enable the H.323 debugging feature 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
debug voip ccapi inout
debug h225 asn1
debug h245 asn1
debug isdn q931

Step 2: run the command clear logto clear the log.
Step 3: run the command show log outto ensure that the buffer is cleared.
Step 4: Make a test call and if the call is on hold verify that the gateway supports the H.245 OpenLogicalChannelAck-Received message that IP is set to "network '0000000'H".

Jan 26 03: 12: 07.558: H245 MSC INCOMING PDU :: =
value MultimediaSystemControlMessage :: = response: openLogicalChannelAck:
forwardLogicalChannelNumber 4
forwardMultiplexAckParameters h2250LogicalChannelAckParameters:
mediaControlChannel unicastAddress: iPAddress:
network '00000000'H
tsapIdentifier 1

Step 5: The excerpt above shows the following:

  • CUCM sends OpenLogicalChannelAck with a fake IP address, either all zeros (as shown above) or as a placeholder for music on hold.
  • This is the default behavior for sending multimedia simplex streaming.
  • If the ISR 4431 is in the call flow, regardless of whether it is a unidirectional or bidirectional direction, the CUCM must inform the gateway of the MOH IP address and port in order to prevent a malicious attack.
  • ISR Generation 2 (G2) platforms (e.g. 2900 and 3900) never check the source IP address and port for incoming RTP packets (Real-Time Transport Protocol). However, the ISR 4431 is a G3 platform (generation 3), which compares incoming RTP packets with the IP address / port of the medium specified in the signaling.
  • If the packets do not match, the ISR G3 discards the packets. This creates a pause when the call is put on hold.

Step 6: Therefore, use the workaround for CUCM shown below to enable duplex streaming for the hold music to avoid a failure of the hold music.

  • Sign in to the Cisco Unified CM administration page.
  • Choose system > Service parameters.
  • Select the serverDrop-down menu and select the publisher node.
  • Choose service and select Cisco CallManager (Active).
  • Click the button Extended.
  • Find the section Cluster-wide parameters (service).
  • Duplex streaming enabled: Default is False (change to True) and click To save.

Note: It is not necessary to restart a service after the above configuration change. This has no business impact and can therefore be done during production hours.