# Troubleshooting Unified CM media resource allocation failures

Canonical: https://warmtransfer.net/knowledge/cucm-media-resource-failures

Last verified: 2026-09-30

Unified CM makes media resources available to calls by placing them in a media resource group list assigned to a device pool or to an individual device[^7]. When a needed resource cannot be allocated, the documented outcomes include a call that connects without supplementary services, a failed call, or fast-busy tone after the user answers[^40][^8][^53].

## How allocation works

By default, an individual device uses the media resources assigned to its device pool[^7]. When a device has a media resource group list on the device itself and another on its device pool, Unified CM searches the device-level list first and then the device pool list[^36].

A media resource group list is an ordered list of groups[^37]. Unified CM must exhaust all resources in one group before it tries a resource from the next group in the same list[^37]. All resources in one media resource group are treated as equal, and Unified CM load shares between resources of each type within the group[^34].

A media resource that is not assigned to any media resource group is automatically placed in the default group[^5]. The default media resource list is always searched as the last resort, either when no resource is available in the device list and the device pool list, or when no list is configured at any level[^6].

## Resource types and stated capacities

### Media termination points

When Unified CM determines that a call endpoint requires an MTP, it allocates the resource from the MTP that has the least active streams[^39]. Release 15 lists these reasons for Unified CM to insert an MTP in the media path[^38]:

- To act as a Trusted Relay Point[^38].
- To convert between IPv4 and IPv6 for RTP streams[^38].
- To deliver SIP Early Offer over SIP trunks[^38].
- To address DTMF transport mismatches[^38].
- To act as an RSVP agent[^38].

The Cisco IP Voice Media Streaming service must be running for the software MTP to be active[^52]. The Release 15 guide states that the Cisco Media Termination Point Software MTP type provides a default of 48 user-configurable MTP resources, depending on network speed and the network interface card[^51]. Sources disagree on software MTP capacity: the Release 12.5(1) troubleshooting guide states that one MTP software application supports 24 calls, which differs from the Release 15 figure[^50].

### Transcoders and Trusted Relay Points

During a call in which the endpoints use different voice codecs, Unified CM invokes a transcoder into the media path[^57]. In addition to codec conversion, a transcoder can provide the same functionality as a media termination point[^58]. A Trusted Relay Point is an MTP or transcoder that Unified CM can insert into the media stream as a control point, and it is enabled by the Trusted Relay Point check box on the MTP or transcoder configuration window[^54].

### Annunciator and conference bridges

The annunciator is activated on a cluster node by turning on the Cisco IP Voice Media Streaming service on that node[^3]. The software conference bridge is created automatically when a Unified CM server is created and cannot be deleted[^48]. Software conference devices support G.711 codecs by default[^49]. A Cisco IOS Enhanced conference bridge supports G.711 a-law/mu-law, G.729, G.729a, G.729b, G.729ab, GSM FR and GSM EFR participants[^13].

| Resource | Stated capacity |
|---|---|
| Annunciator | 48 simultaneous media streams by default[^2] |
| Software conference bridge | At most 256 callers, illustrated in the Release 15 guide as 64 sessions of 4 parties[^47] |
| Cisco IOS Enhanced conference bridge | Up to 8 parties in a single call[^13] |
| Cisco IP Voice Media Streaming software (1 installation) | 16 Unicast Available Conferences of 3 people each, per the Release 12.5(1) troubleshooting guide[^17] |

## What happens when allocation fails

If an MTP resource is not available when it is needed, the call connects without an MTP and that call has no supplementary services[^40]. In Release 15, whether Unified CM fails the call depends on Fail Call If Trusted Relay Point Allocation Fails and Fail Call If MTP Allocation Fails[^8]:

- When Fail Call If Trusted Relay Point Allocation Fails is True, the call is failed regardless of the MTP parameter[^8].
- When it is False and Fail Call If MTP Allocation Fails is True, the call is failed if the MTP is required for an H.323 endpoint, but not if it is required for a SIP endpoint[^8].
- When both are False, the call is not failed[^8].

A Trusted Relay Point is in most instances allocated after the call is answered, so a call that fails because the TRP cannot be allocated may give the user fast-busy tone after answering[^53]. The Release 12.5(1) troubleshooting guide gives the symptom text 'No Conference Bridge Available' and says it could indicate either a software or a hardware problem[^42].

## Codec selection and transcoding

To select an audio codec for a call, Unified CM takes the codecs matching on both sides of the call leg, filters out those exceeding the configured maximum audio bit rate for the region pair, and picks the preferred codec from what remains[^45]. The Release 12.5(1) troubleshooting guide attributes a reorder tone on going off hook to possible codec disagreement between regions[^46]. It directs verifying that both call ends support at least one common codec and using transcoders if they do not[^46].

## Music On Hold

The held party determines the media resource group list that Unified CM uses to allocate a Music On Hold resource[^24]. The Cisco IP Voice Media Streaming Application service must be activated in order to use Music On Hold[^26]. Unicast Music On Hold is the system default and functions without configuring an MOH audio source, MOH server or media resource group list[^33].

Multicast Music On Hold functions only if both media resource groups and media resource group lists are defined to include a multicast MOH server, and at least one audio source must be defined to allow multicasting[^31]. Multicast is enabled on a media resource group by checking the Use Multi-cast for MOH Audio check box[^35]. Multicast Music On Hold supports only IPv4, its audio streams are not encrypted and do not support SRTP, and CTI and MTP devices do not support it[^30]. When an MTP is invoked in a call leg at a multicast MoH site, the Release 15 guide's remedy is to configure unicast MoH or Tone on Hold instead of multicast MoH[^29].

On the Music On Hold server, Maximum Half Duplex Stream is the maximum number of devices that can be on unicast music on hold from that server at one time[^23]. Maximum Multi-cast Connections should be at least the number of devices that might be on multicast MOH at one time[^23]. When a Music On Hold server fails during an active Music On Hold session, the held party hears no music from that point[^32]. The Release 15 guide lists use of the G.729a codec for music as a cause of a user not hearing acceptable Music On Hold, because G.729a is designed for human speech[^22].

## Diagnosing it

Start by confirming that the resource is registered and that the service hosting it is running:[^42][^52]

- For conference failures, the Release 12.5(1) troubleshooting guide directs verifying that software or hardware conference bridge resources are registered with Unified CM[^42].
- When a hardware transcoder is installed but calls between incompatible codecs still fail, the Release 12.5(1) troubleshooting guide gives as a possible cause that no transcoder resources are registered with Unified CM[^10]. It directs checking the ResourceAvailable counter of the Cisco MTP Device object in the Real-Time Monitoring Tool[^10].
- For software MTP, annunciator and Music On Hold, check that the Cisco IP Voice Media Streaming service is running or activated on the relevant node[^52][^3][^26].

MTP devices unregister and disconnect after a hard or soft reset, and reregister with Unified CM after the reset completes[^41]. If the primary Unified CM node fails, a transcoder attempts to register with the next available node in its Unified Communications Manager Group[^56]. A transcoder that is assigned to a media resource group cannot be deleted[^55].

For Cisco IOS DSP farm resources, note that DSP farm services communicate with Unified CM using SCCP and that other protocols are not supported[^12]. In the IOS `associate profile` command, the device name given for registration must match the device name configured in Unified CM; otherwise the DSP farm profile is not registered to Unified CM[^15]. The IOS interoperability guide verifies DSP farm registration with `show sccp ccm group`, `show dspfarm profile`, `show sccp connections` and `show dspfarm all`[^16].

## See also

- [Unified CM device pools and device configuration model](https://warmtransfer.net/knowledge/cucm-device-pools)
- [Unified CM SIP trunks and security profiles](https://warmtransfer.net/knowledge/cucm-sip-trunks)
- [Unified CM service parameters that change transfer behaviour](https://warmtransfer.net/knowledge/cucm-service-parameters-for-transfer)
- [CUCM CallManager SDL trace files](https://warmtransfer.net/knowledge/cucm-sdl-trace-files)

## Applicability

Applies to: Cisco Unified Communications Manager and Cisco IOS voice gateway DSP farm. Deployments: on-premises. Sources checked 2026-09-30. MTP, transcoder, Trusted Relay Point, annunciator, conference bridge and Music On Hold configuration details come from the Release 15 and SUs guides[^38][^47][^24]. Symptom and troubleshooting guidance comes from the Release 12.5(1) troubleshooting guide[^42][^46]. DSP farm verification guidance comes from the IOS interoperability guide[^16].

## What remains uncertain

Sources disagree on software MTP capacity, with 24 calls per application in Release 12.5(1) and a default of 48 resources in Release 15, so verify the figure for your release[^50][^51]. The default values of Fail Call If MTP Allocation Fails and Fail Call If Trusted Relay Point Allocation Fails are not covered by the sources below. The Supported MOH Codecs service parameter and its default in Release 15 are not covered by the sources below. The full definition of the MediaResourceListExhausted alarm and its media resource type values are not covered by the sources below. Release 15 lists SIP Early Offer over SIP trunks and DTMF transport mismatches as reasons to insert an MTP[^38]. How much MTP demand those drivers create, and the MTP Required setting on SIP trunks, are not covered by the sources below. The documented Music On Hold failure case covers a server failing during an active session[^32]. What the held party hears when no Music On Hold resource can be allocated at all, including any Tone on Hold fallback, is not covered by the sources below. How a conference bridge is selected through the conference controller's media resource group list is not covered by the sources below. Allocation failures for conference bridge types other than the software and Cisco IOS Enhanced conference bridges, including SIP-based conference bridges, are not covered by the sources below. Field patterns for Cisco IOS media resource registration failures are not covered by the sources below.

## Sources

[^1]: The Release 12.5(1) Managed Services Guide lists MediaResourceListExhausted, MtpNoMoreResourcesAvailable, ConferenceNoMoreResourcesAvailable and MohNoMoreResourcesAvailable among its Warning-Level Alarms. Source: [Managed Services Guide for Cisco Unified Communications Manager and IM and Presence Service - Cisco Unified Serviceability Alarms and CiscoLog Messages](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/managed_services/12_5_1/cucm_b_managed-services-guide-1251/cucm_b_managed-services-guide-1251_chapter_0101.html), chapter 'Cisco Unified Serviceability Alarms and CiscoLog Messages', section 'Warning-Level Alarms' (table of contents entries). Checked 2026-09-30.
[^2]: By default an annunciator supports 48 simultaneous media streams. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Annunciator Scalability'. Checked 2026-09-30.
[^3]: The annunciator is activated on a cluster node by turning on the Cisco IP Voice Media Streaming service on that node. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Annunciator Overview'. Checked 2026-09-30.
[^4]: For the error ConferenceNoMoreResourcesAvailable (No more Conference Resources available), the technote directs checking under Media Resources > Conference Bridge that all hardware conference bridges are registered and that media resources are distributed appropriately through the device pool configuration. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Troubleshoot', first problem. Checked 2026-09-30.
[^5]: A media resource that is not assigned to any media resource group is automatically placed in the default group. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Media Resource Groups and Media Resource Group Lists'. Checked 2026-09-30.
[^6]: The default media resource list is always searched, as the last resort, when no resource is available in the device list and the device pool list or when no list is configured at any level. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Media Resource Groups and Media Resource Group Lists'. Checked 2026-09-30.
[^7]: In Release 15, media resources are made available to calls by putting them in a media resource group list assigned to a device pool or to an individual device, and an individual device by default uses the media resources assigned to its device pool. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'About Media Resources'. Checked 2026-09-30.
[^8]: In Release 15 the call is failed when Fail Call If Trusted Relay Point Allocation Fails is True regardless of the MTP parameter; when it is False and Fail Call If MTP Allocation Fails is True the call is failed if the MTP is required for an H.323 endpoint but not if it is required for a SIP endpoint; when both are False the call is not failed. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), table of Fail Call If TRP Allocation Fails / Fail Call If MTP Allocation Fails / Unified CM Fails Call? (returned under 'Transcoders with MTP Functionality'; may sit under the Trusted Relay Point sections). Checked 2026-09-30.
[^9]: For a fast busy when calling a remote location, the technote's remedy is to put software and hardware transcoder resources in separate media resource groups and place the hardware transcoder group first in the media resource group list. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Troubleshoot', second problem. Checked 2026-09-30.
[^10]: When a hardware transcoder is installed but calls between incompatible codecs still fail, the Release 12.5(1) troubleshooting guide gives as a possible cause that no transcoder resources are registered with Unified CM and directs checking the ResourceAvailable counter of the Cisco MTP Device object in the Real-Time Monitoring Tool. Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'Hardware Transcoder Not Working As Expected'. Checked 2026-09-30.
[^11]: An IOS DSP farm profile must be enabled with no shutdown, which allocates DSP farm resources and associates the application, and its maximum sessions value defaults to 0. Source: [Cisco Unified Communications Manager and Cisco IOS Interoperability Guide, Release 15.1 - Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers](https://www.cisco.com/c/en/us/td/docs/ios/voice/cminterop/configuration/guide/15_1/vc_15_1_book/vc_enh_confr_vgr.html), chapter 'Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers', DSP farm profile procedure, maximum sessions and no shutdown steps. Checked 2026-09-30.
[^12]: Cisco IOS DSP farm services communicate with Unified CM using SCCP; other protocols are not supported. Source: [Cisco Unified Communications Manager and Cisco IOS Interoperability Guide, Release 15.1 - Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers](https://www.cisco.com/c/en/us/td/docs/ios/voice/cminterop/configuration/guide/15_1/vc_15_1_book/vc_enh_confr_vgr.html), chapter 'Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers', prerequisites/restrictions. Checked 2026-09-30.
[^13]: A Cisco IOS Enhanced conference bridge allows up to eight parties in a single call and supports G.711 a-law/mu-law, G.729, G.729a, G.729b, G.729ab, GSM FR and GSM EFR participants. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Conference Bridges](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01100.html), section 'Conference Bridge Types', Cisco IOS Enhanced Conference Bridge. Checked 2026-09-30.
[^14]: In the IOS 15.1 interoperability guide, hardware MTPs support only G.711 a-law and G.711 u-law, and only one codec is supported for each MTP profile. Source: [Cisco Unified Communications Manager and Cisco IOS Interoperability Guide, Release 15.1 - Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers](https://www.cisco.com/c/en/us/td/docs/ios/voice/cminterop/configuration/guide/15_1/vc_15_1_book/vc_enh_confr_vgr.html), chapter 'Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers', MTP restrictions. Checked 2026-09-30.
[^15]: The device name given in the IOS associate profile ... register command must match the device name configured in Unified CM; otherwise the DSP farm profile is not registered to Unified CM. Source: [Cisco Unified Communications Manager and Cisco IOS Interoperability Guide, Release 15.1 - Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers](https://www.cisco.com/c/en/us/td/docs/ios/voice/cminterop/configuration/guide/15_1/vc_15_1_book/vc_enh_confr_vgr.html), chapter 'Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers', procedure for associating a DSP farm profile to a Cisco Unified Communications Manager group, associate profile step. Checked 2026-09-30.
[^16]: The IOS interoperability guide verifies DSP farm registration with show sccp ccm group, show dspfarm profile, show sccp connections and show dspfarm all. Source: [Cisco Unified Communications Manager and Cisco IOS Interoperability Guide, Release 15.1 - Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers](https://www.cisco.com/c/en/us/td/docs/ios/voice/cminterop/configuration/guide/15_1/vc_15_1_book/vc_enh_confr_vgr.html), chapter 'Configuring Enhanced Conferencing and Transcoding for Voice Gateway Routers', verification procedure. Checked 2026-09-30.
[^17]: The Release 12.5(1) troubleshooting guide states that one installation of the Cisco IP Voice Media Streaming software supports 16 Unicast Available Conferences of three people per conference. Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'No Available Conference Bridge'. Checked 2026-09-30.
[^18]: The multicast MoH through CUBE technote uses the CLI command show perf query class "Cisco MOH Device" to verify allocation and to see whether the MOHOutOfResources count increments. Source: [MMoH through CUBE Operation, Configuration, and Troubleshoot Guide](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/116392-technote-product-00.html), section 'Troubleshoot'. Checked 2026-09-30.
[^19]: The multicast MoH through CUBE technote treats hearing only a tone on hold instead of multicast MoH as a sign that Unified CM did not allocate multicast MoH. Source: [MMoH through CUBE Operation, Configuration, and Troubleshoot Guide](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/116392-technote-product-00.html), section 'Troubleshoot'. Checked 2026-09-30.
[^20]: In the Unified CM 8.x design guide, the codecs allowed for MoH streams are chosen in the Supported MoH Codecs clusterwide service parameter of the IP Voice Media Streaming application, and by default only G.711 mu-law is selected. Source: [Cisco Unified Communications System 8.x SRND - Music on Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/moh.html), chapter 'Music on Hold' (chapter 18), codec discussion; heading not returned. Checked 2026-09-30.
[^21]: The multicast MoH through CUBE technote recommends assigning the MoH server a dedicated region with the inter-region codec set to G.711, because the MoH codec depends on the relationship between the MoH server region and the trunk or gateway region. Source: [MMoH through CUBE Operation, Configuration, and Troubleshoot Guide](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/116392-technote-product-00.html), section 'Configure MMoH'. Checked 2026-09-30.
[^22]: The Release 15 guide lists use of the G.729a codec for music as a cause of a user not hearing acceptable Music On Hold, because G.729a is designed for human speech. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), sections 'Music On Hold Restrictions' (Unacceptable Audio Quality with G.729a codec) and 'Music On Hold Troubleshooting'. Checked 2026-09-30.
[^23]: On the Music On Hold server, Maximum Half Duplex Stream is the maximum number of devices that can be on unicast music on hold from that server at one time, and Maximum Multi-cast Connections should be at least the number of devices that might be on multicast MOH at one time. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Configure Music On Hold Server'. Checked 2026-09-30.
[^24]: The held party determines the media resource group list that Unified CM uses to allocate a Music On Hold resource. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Music On Hold Interactions', Media Resource Selection. Checked 2026-09-30.
[^25]: In the Unified CM 8.x design guide, the User Hold MoH Audio Source configured for the holder determines the audio file streamed, while the holdee's media resource group list determines the server the stream comes from. Source: [Cisco Unified Communications System 8.x SRND - Music on Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/moh.html), chapter 'Music on Hold' (chapter 18), MoH resource selection discussion; heading not returned. Checked 2026-09-30.
[^26]: The Cisco IP Voice Media Streaming Application service must be activated in order to use Music On Hold. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Activate Cisco IP Voice Media Streaming'. Checked 2026-09-30.
[^27]: With multicast MOH and an ISR 4431 gateway, external callers on hold hear silence because the gateway discards MOH RTP that does not match the media address in signalling; the documented fix is to set the Cisco CallManager clusterwide service parameter Duplex Streaming Enabled to True, with no service restart required. Source: [Troubleshoot Music On Hold Failure When Gateway is Integrated Service Router 4431](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/212640-troubleshoot-music-on-hold-failure-when.html), sections 'Problem' and 'Solution'. Checked 2026-09-30.
[^28]: The Release 15 Music On Hold chapter describes the outcome of an MTP being invoked in a call leg at a multicast MoH site in two different ways: under Restrictions, Unified CM falls back to unicast MOH; under Troubleshooting, the caller receives silence instead of Music On Hold (disputed). Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), sections 'Music On Hold Restrictions' and 'Music On Hold Troubleshooting' (Music On Hold Does Not Play on Phone). Checked 2026-09-30.
[^29]: For the case of an MTP invoked in a call leg at a multicast MoH site, the Release 15 guide's remedy is to configure unicast MoH or Tone on Hold instead of multicast MoH. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Music On Hold Troubleshooting', Music On Hold Does Not Play on Phone. Checked 2026-09-30.
[^30]: Multicast Music On Hold supports only IPv4, its audio streams are not encrypted and do not support SRTP, and CTI and MTP devices do not support it. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Music On Hold Restrictions'. Checked 2026-09-30.
[^31]: Multicast Music On Hold functions only if both media resource groups and media resource group lists are defined to include a multicast MOH server, and at least one audio source must be defined to allow multicasting. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Unicast and Multicast Audio Sources'. Checked 2026-09-30.
[^32]: When a Music On Hold server fails during an active Music On Hold session, the held party hears no music from that point. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Music On Hold Failover and Fallback'. Checked 2026-09-30.
[^33]: Unicast Music On Hold is the system default and functions without configuring an MOH audio source, MOH server or media resource group list. Source: [Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Music On Hold](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/cucm_b_feature-configuration-guide-for-15/cucm_mp_m7ca6519_00_music-on-hold-12-0.html), section 'Unicast and Multicast Audio Sources'. Checked 2026-09-30.
[^34]: All resources in one media resource group are treated as equal, and Unified CM load shares between resources of each type within the group. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Media Resource Groups and Media Resource Group Lists'. Checked 2026-09-30.
[^35]: Multicast Music On Hold audio is enabled on a media resource group by checking the Use Multi-cast for MOH Audio check box. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Resources Configuration Task Flow', media resource group procedure. Checked 2026-09-30.
[^36]: When a device has a media resource group list on the device itself and another on its device pool, Unified CM searches the device-level list first and then the device pool list. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Media Resource Groups and Media Resource Group Lists'. Checked 2026-09-30.
[^37]: A media resource group list is an ordered list of groups, and all resources in one group must be exhausted before Unified CM tries a resource from the next group in the same list. Source: [Configure Media Resource Groups and Group Lists](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/213261-understanding-media-resource-groups-and.html), section 'Media Resource Groups and Media Resource Group Lists'. Checked 2026-09-30.
[^38]: Release 15 lists these reasons for Unified CM to insert an MTP in the media path: to act as a Trusted Relay Point, to convert between IPv4 and IPv6 for RTP streams, to deliver SIP Early Offer over SIP trunks, to address DTMF transport mismatches, and to act as an RSVP agent. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Termination Points'. Checked 2026-09-30.
[^39]: When Unified CM determines that a call endpoint requires an MTP, it allocates the resource from the MTP that has the least active streams. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Termination Points'. Checked 2026-09-30.
[^40]: If an MTP resource is not available when it is needed, the call connects without an MTP and that call has no supplementary services. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Termination Points'. Checked 2026-09-30.
[^41]: MTP devices unregister and disconnect after a hard or soft reset, and reregister with Unified CM after the reset completes. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Termination Points Interactions and Restrictions'. Checked 2026-09-30.
[^42]: The Release 12.5(1) troubleshooting guide gives the symptom text 'No Conference Bridge Available', says it could indicate either a software or a hardware problem, and directs verifying that software or hardware conference bridge resources are registered with Unified CM. Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'No Available Conference Bridge'. Checked 2026-09-30.
[^43]: For 'No Conference Bridge Available' the Release 12.5(1) troubleshooting guide also directs checking the Unicast AvailableConferences counter in the Real-Time Monitoring Tool, the maximum number of users configured for ad hoc and meet-me conferences, and the Audio Bandwidth setting in the Location Configuration window. Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'No Available Conference Bridge', recommended action. Checked 2026-09-30.
[^44]: The Release 12.5(1) troubleshooting guide attributes an established call with no supplementary services on an H.323 device that does not support H.323v2 to a possible MTP resource problem, and directs verifying that MTP resources are registered and that Media Termination Point Required is checked in the gateway configuration. Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'No Supplementary Services Are Available on an Established Call'. Checked 2026-09-30.
[^45]: To select an audio codec for a call, Unified CM takes the codecs matching on both sides of the call leg, filters out those exceeding the configured maximum audio bit rate for the region pair, and picks the preferred codec from what remains. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Core Settings for Device Pools](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_0111.html), section 'Regions Overview'. Checked 2026-09-30.
[^46]: The Release 12.5(1) troubleshooting guide attributes a reorder tone on going off hook to possible codec disagreement between regions, and directs verifying that both call ends support at least one common codec and using transcoders if they do not. Source: [Troubleshooting Guide for Cisco Unified Communications Manager Release 12.5(1) — Device Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0100.html), section 'Codec and Region Mismatches'. Checked 2026-09-30.
[^47]: The software conference bridge supports at most 256 callers, which the Release 15 guide illustrates as 64 conference sessions of 4 parties each. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Conference Bridges](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01100.html), section 'Conference Bridge Types', software conference bridge. Checked 2026-09-30.
[^48]: The software conference bridge is created automatically when a Unified CM server is created and cannot be deleted. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Conference Bridges](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01100.html), section 'Conference Bridge Types', software conference bridge. Checked 2026-09-30.
[^49]: Software conference devices support G.711 codecs by default. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Conference Bridges](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01100.html), section 'Conference Bridge Types', software conference bridge. Checked 2026-09-30.
[^50]: The Release 12.5(1) troubleshooting guide states that one MTP software application supports 24 calls, which differs from the Release 15 configuration guide figure of a default of 48 software MTP resources (disputed). Source: [Troubleshooting Guide for Cisco Unified Communications Manager, Release 12.5(1) - Cisco Unified Communications Manager Services Issues](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0110.html), section 'No Supplementary Services Are Available on an Established Call'. Checked 2026-09-30.
[^51]: The Release 15 guide states that the Cisco Media Termination Point Software MTP type provides a default of 48 user-configurable MTP resources, depending on network speed and the network interface card. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), MTP types table, row 'Cisco Media Termination Point Software'. Checked 2026-09-30.
[^52]: The Cisco IP Voice Media Streaming service must be running for the software MTP to be active. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Media Termination Points'. Checked 2026-09-30.
[^53]: A Trusted Relay Point is in most instances allocated after the call is answered, so a call that fails because the TRP cannot be allocated may give the user fast-busy tone after answering. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Trusted Relay Points Interactions and Restrictions'. Checked 2026-09-30.
[^54]: A Trusted Relay Point is an MTP or transcoder that Unified CM can insert into the media stream as a control point, enabled by the Trusted Relay Point check box on the MTP or transcoder configuration window. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Trusted Relay Point Overview'. Checked 2026-09-30.
[^55]: A transcoder that is assigned to a media resource group cannot be deleted. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Transcoder Interactions and Restrictions'. Checked 2026-09-30.
[^56]: If the primary Unified CM node fails, a transcoder attempts to register with the next available node in its Unified Communications Manager Group. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Transcoder Interactions and Restrictions'. Checked 2026-09-30.
[^57]: During a call in which the endpoints use different voice codecs, Unified CM invokes a transcoder into the media path. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Transcoders'. Checked 2026-09-30.
[^58]: In addition to codec conversion, a transcoder can provide the same functionality as a media termination point. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Media Resources](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01011.html), section 'Transcoders with MTP Functionality'. Checked 2026-09-30.