/mcpInteraction Feature Cisco Unified Communications Manager supports MOH on a reverted call if MOH is configured for a normal held call. Hold Reversion Held parties determine the media resource group list that a Cisco Unified Communications Manager uses to allocate a Music On Hold resource. Media Resource Selection Cisco Unified Communications Manager enhances the Cisco IP Voice Media Streaming application service to support Secure Real-Time Protocol (SRTP). Hence, when you enable the Cisco Unified Communications Manager cluster or system for security, the MOH server registers with Cisco Unified Communications Manager as an SRTP capable device. If the receiving device is also SRTP-capable, the music media is encrypted before streaming to the receiving device. Make sure of the following: • Cluster security should be mixed mode—Run the utils ctl set-cluster mixed-mode CLI command • SIP trunks in the path support SRTP—The SRTP Allowed check box must be checked in the Trunk Configuration window for SRTP to work over the trunk. • Devices support SRTP—In the Phone Security Profile used by the endpoint, the Device Security Mode must be Encrypted. Secured Music On Hold with SRTP Music On Hold Restrictions Description Restriction Computer Telephony Integration (CTI) and media termination point (MTP) devices do not support the multicast Music On Hold feature. If you configure CTI or MTP devices with a multicast MoH device in the media resource group list of the CTI device, call control issues may result. CTI and MTP devices do not support multicast media streaming. Multicast Music On Hold Support Multicast Music On Hold supports only IPv4. The Cisco IP Voice Media Streaming Application, which is a component of Music On Hold, supports both IPv4 and IPv6 audio media connections for unicast Music On Hold. Multicast Music On Hold supports IPv4 only. Devices with an IP addressing mode of IPv6 only cannot support multicast. Internet Protocol Support Cisco Unified Communications Manager does not support distribution of fixed-device (hardware) audio sources across Music On Hold servers within a media resource group. Distribution of fixed-device audio sources Because the G.729a codec is designed for human speech, if you use it with Music On Hold for music, it may not provide acceptable audio quality. Unacceptable Audio Quality with G.729a codec Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs 630 Custom Features Music On Hold Restrictions