/mcpDescription Restriction • If you provide only one MOH audio source identifier in the SIP header, including if a comma appears before or after the MOH audio source identifier value, the same MOH ID is used for both user and network MOH. The SIP trunk populates both the user and the network MOH audio source identifiers in the SIP header so that Call Control always receive both values. • If there are more than two MOH audio source identifier values separated by a comma in the header, then the first two values are used. Subsequent values are ignored. MOH Audio Source Identifier Administrators are responsible to maintain consistent caller-specific MOH configurations when multiple Cisco Unified Communications Manager clusters are involved. Administrators for Consistent Caller-specific MOH Configurations The original incoming caller to the call center cannot change during the course of the entire call. Original Incoming Caller The Music On Hold information is shared only across SIP trunks. MOH Information Music On Hold Troubleshooting Music On Hold Does Not Play on Phone Phone user cannot hear Music On Hold. • G.729a codec is used with MOH for music, which may not provide acceptable audio quality. • An MTP resource is invoked in a call leg at a site that is using multicast MoH. • When an MTP resource gets invoked in a call leg at a site that is using multicast MoH, the caller receives silence instead of Music On Hold. To avoid this scenario, configure unicast MoH or Tone on Hold instead of multicast MoH. Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs 632 Custom Features Music On Hold Troubleshooting