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New Member

MoH from CM to PSTN via Voice gateway

We are running CM 6.1.4 and enabled the network for MoH on multicast. The internal IP to IP phone is working on multicast MoH as shown by RTMT, however PSTN calls continue to show a Unicast MoH from RTMT.

We did verify network multicast functionality upto Voice gateway by enabling loopback interface with "ip igmp join <mcast address>" and ensuring show ip mroute displays incoming interface correctly as well as outgoing interface as loopback 0 interface.

The music is being played for PSTN receiver but RTMT still shows a unicast MoH resource active.

What is the reason for this? What configuration change, if at all, is needed to make MoH sent as multicast to PSTN on ISDN (on Voice gateway)

Thanks, Surya

New Member

Re: MoH from CM to PSTN via Voice gateway

have you checked that the gateway has the correct MRGL assigned - ie. the MRGL with the MRG that has the MoH resource in it??  If the gateway doens't have any MRGL it will use what ever MoH resource is not assigned to any MRG

hope that helps,


Re: MoH from CM to PSTN via Voice gateway

Make sure to reset the MRGL as well for all changes to propagate, I have run into issues were the config on the webpages si not reflected on real life operation because the MRGL was not reset after the last change.

Cisco Employee

Re: MoH from CM to PSTN via Voice gateway

By any chance is the call using MTP???

Note The following restriction exists  for multicast music on hold (MOH) when a media termination point (MTP)  is invoked. When an MTP resource gets invoked in a call leg at a site  that is using multicast MOH, the caller hears silence instead o music on  hold. To avoid this scenario, configure unicast MOH or Tone on Hold  instead of multicast MOH



If this helps, please rate



if this helps, please rate
New Member

Re: MoH from CM to PSTN via Voice gateway

Sorry for the delay and thank you all for your responses. They were helpful to look at configs once again for any errors.

The problem is resolved now after troubleshooting for over a week with the help of several techies including TAC.

The behaviour was due to the voice gateway router becoming the DR on the LAN segment instead of Layer-3 switch connecting the WAN router and the voice gateway router. Call manager is located remotely and the muticast traffic needs to be received from the WAN through the Layer-3 switch to the voice gateway router and then played on the ISDN PRI PSTN call.

The solution has been to make the Layer-3 Switch vlan inteface to become the DR for multicast on the LAN segment. This was accomplished by

Layer-3-Switch# (config) int vlan300

                                      ip pim dr-priority 110

On the backup L-3 switch

Layer-3-backup-Switch# (config) int vlan300

                                      ip pim dr-priority 100

This made the L-3 switch as the DR and the (S,G) tree showed correct source which is the call manager.

Also, we needed to disable pim on loopback interface of the voice gateway routers by  "no ip pim sparse-mode".

All looks good now !!!