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configure Multicast MOH from the Branch Router Flash.Multicast MOH from the branch router flash is a feature for multisite deployments thatuse centralized call processing.

The feature works only with multicast MOH and is based on MOH capabilities of Cisco

Unified SRST. The Cisco IOS SRST gateway is configured for multicast MOH andcontinuously sends a MOH stream, regardless of its SRST mode (standby or fallbackmode).

Neither CUCM nor the remote IP Phones are aware that the SRST gateway is involved.To them it appears as though a multicast MOH stream has been generated by theCUCM MOH server and received by the remote IP Phones.

Therefore, the remote Cisco IP Phones are configured to use the centralized CUCMMOH server as their MOH source. The CUCM MOH server is configured for multicast

MOH (mandatory), and the max-hops value in the MOH server configuration is set to 1for the affected audio sources. The max-hops parameter specifies the Time to Live(TTL) value that is used in the IP header of the RTP packets. The CUCM MOH serverand the Cisco IOS SRST gateway located at the remote site have to use the samemulticast address and port number for their streams. This way, MOH packets generatedby the CUCM MOH server at the central site are dropped by the central-site routerbecause the TTL has been exceeded. As a consequence, the MOH packets do not cross

the IP WAN. The SRST gateway permanently generates a multicast MOH stream withan identical multicast IP address and port number so that the Cisco IP Phones simplylisten to this stream as it appears to be coming from the CUCM MOH server.Instead of setting the max-hops parameter for MOH packets to 1, you can use oneof thefollowing methods:

* Configure an access control list (ACL) on the WAN interface at the central site: Thisprevents packets that are destined for the multicast group address or addressesfrom

being sent out the interface.* Disable multicast routing on the WAN interface: Do not configure multicast routingon the WAN interface to ensure that multicast streams are not forwarded into theWAN.

When using multicast MOH from branch router flash, G.711 has to be enabled betweenthe CUCM MOH server and the remote Cisco IP Phones. This is necessary because thebranch SRST MOH feature supports only G.711. Therefore, the stream that is set up byCUCM in the signaling messages also has to be G.711. Because the packets are not

sentacross the WAN, configuring the high-bandwidth G.711 codec is no problem as longas

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it is enabled only for MOH. All other audio streams (such as calls between phones) thatare sent over the WAN should use the low-bandwidth G.729 codec.

A Cisco Unified SRST license is required regardless of whether the SRST functionalitywill actually be used. The license is required because the configuration for str

eamingmulticast MOH from branch router flash is done in SRST configuration mode. Also,even if SRST functionality will not be used, at least one max-ephones for everyCiscoIP Phone supported and at least one max-dn for every directory number (dn) on allphones must be configured.

I hope this information helps clarify how this works and as explained before toget thisconfiguredIt will be necessary to open a new case with our gateway team (multi services).

Really this needs to be setup across the WAN or on a network topologywhere the multicast stream from the CallManager cannot possibly reachthe router.

The router's configuration is missing:1. ip multicast-routing

2. ip pim statements under the interfaces, I typically used "ip pimsparse-dense" but what you select ultimately depends on your network and

multicast configuration.

3. A loopback interface. This is required in order for multicast mohaudio to be heard on the gateway during regular operation. For example:

interface loopback 0no shutdownip address 1.1.1.1 255.255.255.0