# Unified CM media resources

Canonical: https://warmtransfer.net/knowledge/cucm-media-resources

Last verified: 2026-09-25

Unified CM 15 media resource types comprise annunciators, interactive voice response (IVR), media termination points (MTP), transcoders, trusted relay points (TRP), conference bridges, and music on hold/video on hold[^50]. Media resources are made available to calls by placing them in a media resource group list (MRGL), which is assigned to an individual device or to a device pool[^35].

## Resource allocation and grouping

A media resource group (MRG) can contain annunciators, IVRs, conference bridges, MTPs, music on hold (MOH) servers, and transcoders[^34]. All resources in an MRG are treated as equal, and Unified CM shares load across resources of each type within that group[^33]. An MRGL is a prioritized list of MRGs, and resources are selected from the groups according to the priority order configured in the list[^36]. Unified CM selects a resource from the next MRG in an MRGL only after every resource in the current MRG is exhausted[^32]. A media resource that is not assigned to any MRG automatically becomes part of the default MRGL[^7].

By default, an individual device uses the media resources assigned to its device pool[^8]. When a device has an MRGL assigned directly to the device and another assigned to its device pool, Unified CM searches the device-level MRGL first, followed by the device pool MRGL[^9]. When a call departs via a gateway and requires an MTP, the MTP is chosen from that gateway's MRGL[^38]. For a conference, the conference bridge is chosen from the MRGL of the conference controller that initiates the conference[^3].

In the Release 15 task flow, an administrator activates software media resources first via the Cisco IP Voice Media Streaming service[^56]. The workflow then configures MTPs, transcoders, IVR, and the annunciator, sets up MRGs, builds MRGLs, and assigns them to devices or device pools, with announcements treated as optional later steps[^56]. Activating the Cisco IP Voice Media Streaming service enables the annunciator, IVR, MTP, software conference bridge, and MOH resources on Unified CM[^12].

## Media termination points and transcoders

The Release 15 guide identifies 3 MTP implementations: software MTPs on IOS gateways, hardware MTPs on IOS gateways, and the software MTP hosted by the Cisco IP Voice Media Streaming service[^46]. By default, the Cisco Media Termination Point Software type provides 48 MTP resources, which can be modified[^55]. On a 10-Mb network interface or network, this software MTP provides approximately 24 MTP resources[^54]. When Unified CM allocates an MTP for an endpoint, it chooses the MTP with the fewest active streams[^40]. Neither system users nor the endpoint for which an MTP was inserted can see that an MTP is active on the call[^39].

Unified CM 15 lists several triggers for inserting an MTP:
- Resolving mismatches in DTMF transport between call legs[^41].
- Delivering SIP Early Offer over SIP trunks[^42].
- Converting RTP streams between IPv4 and IPv6[^44].
- Handling H.323 supplementary services for endpoints that support neither Empty Capability Set (ECS) nor FastStart[^43].

Cisco's MTP tech note also states that an MTP device can be allocated due to DTMF or RSVP requirements[^45].

A transcoder converts an incoming media stream in one codec to an outgoing stream in another codec, and Unified CM inserts one when endpoints on a call use different voice codecs[^57]. When a call requires both transcoding and MTP services, Unified CM assigns a transcoder because it can handle both functions simultaneously[^58]. A Trusted Relay Point (TRP) is an MTP or transcoder inserted into the media stream; a transcoder becomes a TRP when the Trusted Relay Point check box is enabled[^60].

## Gateways and DSP resources

DSPs on IOS XE gateways can act as media resources for transcoding or transrating, communicating with Unified CM over (Secure) SCCP[^10]. On CUBE, LTI-based transcoding accesses DSP resources through an internal API without requiring a TCP socket or registration, relying solely on a DSPFARM profile tied to application type CUBE[^17]. PVDM4 modules support Opus transcoding when using CUBE LTI-based transcoding[^49].

The ISR 4000 software MTP bridges media across 2 connections so Unified CM can relay calls routed through SIP or H.323 endpoints[^14]. It registers with Unified CM via SCCP, and its capacity is defined by the `maximum sessions software` command[^14]. For the ISR 4000 software MTP to operate, codec and packetization settings must match on the inbound and outbound call legs[^15]. Reported restrictions for the ISR 4000 software MTP include no hardware MTP for repacketization, no per-call debugging, no call threshold for standalone software MTP, and no RSVP agent[^13].

## Conference bridges, annunciators, and IVR

Release 15 conference bridge types include Cisco Conference Bridge Software, Cisco IOS Conference Bridge, Cisco IOS Enhanced Conference Bridge, IOS heterogeneous, homogeneous, and guaranteed audio video conference bridges, Cisco TelePresence MCU, Cisco TelePresence Conductor, Cisco Meeting Server, and legacy hardware options[^4]. Software conference bridge devices default to supporting G.711 codecs[^52]. A software conference bridge supports up to 256 callers, accommodating 64 4-party conference sessions at that limit[^51]. The software bridge combines audio using a simple summing algorithm, which can result in low volume and degraded audio quality when conferences have high participant counts[^53].

An annunciator is an SCCP software device used by Unified CM to stream prerecorded messages and tones, supporting 48 simultaneous media streams by default[^2][^1]. The IVR device plays prerecorded feature announcements and supports 48 simultaneous callers by default[^16].

## Music on Hold

Activating the Cisco IP Voice Media Streaming Application service is required to enable Music On Hold[^28]. MOH is invoked as user hold when a user triggers the Hold softkey or button, or as network hold automatically when activating Transfer, Conference, or Call Park[^23]. Unified CM selects an MOH resource based on the held party's MRGL, using the device-level MRGL or, if none is assigned, the device pool MRGL[^22].

| MOH delivery mode | Transport target | Protocol limitation |
| --- | --- | --- |
| Unicast | Directly to requesting endpoint[^31] | not covered by the sources below |
| Multicast | Multicast group IP address joined by endpoints[^31] | IPv4 only[^24] |

For multicast MOH, the MRG must include an MOH server configured for multicast and have the Use Multicast for MOH Audio check box selected[^25]. Unified CM MOH supports G.711 mu-law, G.711 a-law, G.729, and L16 256K wideband codecs[^19]. While the MOH server transcodes among G.711 mu-law, G.711 a-law, and L16 256K, it cannot transcode for G.729[^26]. Cisco warns that the G.729a codec may produce unacceptable music quality[^21].

If an MOH server goes offline during an active session, the held endpoint hears silence, but active call functions continue without disruption[^29]. For caller-specific MOH, if user and network MOH audio source identifiers are unprovisioned, the MOH information in the SIP header is ignored and the call reverts to tone on hold[^30]. When running the Cisco IP Voice Media Streaming Application on a dedicated server using the 7500 or 10K OVA, documented capacity is 1000 held callers, 500 MOH sources, and 300 to 700 annunciator callers using a single MOH codec[^20].

## See also

- See also [Unified CM call admission control](https://warmtransfer.net/knowledge/cucm-call-admission-control).
- See also [Unified CM device pools and device configuration model](https://warmtransfer.net/knowledge/cucm-device-pools).
- See also [Unified CM SIP trunks and security profiles](https://warmtransfer.net/knowledge/cucm-sip-trunks).
- See also [SIP 488 and codec negotiation failures](https://warmtransfer.net/knowledge/sip-488-codec-failures).

## Applicability

Applies to: Cisco Unified Communications Manager, Cisco 4000 Series ISR (IOS XE), and Cisco Unified Border Element (IOS XE). Deployments: on-premises. Sources checked 2026-09-25. Unified CM media resource behaviors and types are documented for Release 15 and SUs[^50]. General MRG and MRGL selection rules apply to 11.x and later[^7]. The Cisco 4000 Series ISR software MTP is documented on Cisco IOS XE[^14]. DSP media resources on IOS XE gateways communicate with Unified CM using (Secure) SCCP[^10]. CUBE LTI-based transcoding accesses DSP resources through an internal API[^17].

## What remains uncertain

SIP Profile Early Offer modes (Mandatory insert MTP if needed vs Best Effort no MTP) and the SIP trunk MTP Required check box are not covered by the sources below. Codec and packetization support of the Unified CM IPVMS software MTP is not covered by the sources below. The exact DTMF method pairs (RFC 2833 vs KPML vs out-of-band) that make Unified CM insert an MTP are not covered by the sources below. The order of precedence for MOH audio source selection across directory number, device, device pool, and service parameters is not covered by the sources below. Whether SCCP DSP farms registered to Unified CM are supported on current IOS XE (17.x) ISR and Catalyst devices is not covered by the sources below. Cisco Meeting Server configuration as a Unified CM conference bridge over a SIP trunk and its MRG placement are not covered by the sources below. PVDM4 session counts for transcoding and conferencing per codec complexity are not covered by the sources below. Intelligent Bridge Selection and preference mechanisms for video versus audio conference bridges are not covered by the sources below.

## Sources

[^1]: 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), Annunciator (overview). Checked 2026-09-25.
[^2]: The annunciator is an SCCP software device that lets Unified CM play prerecorded messages and tones to devices. 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), Annunciator (overview). Checked 2026-09-25.
[^3]: The conference bridge is chosen from the MRGL of the conference controller, the party that initiates the conference. 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), Which MRGL is used / Conference Bridges. Checked 2026-09-25.
[^4]: The Release 15 conference bridge types include Cisco Conference Bridge Software, Cisco IOS Conference Bridge, Cisco IOS Enhanced Conference Bridge, the IOS heterogeneous, homogeneous and guaranteed audio video conference bridges, Cisco TelePresence MCU, Cisco TelePresence Conductor, and Cisco Meeting Server, as well as legacy hardware types. 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), Conference Bridge Types. Checked 2026-09-25.
[^5]: The CUBE IOS XE 17.6+ transcoding chapter says SCCP-based transcoding is not supported with IOS XE releases and that CUBE uses LTI instead. This appears to conflict with the IOS XE 16.12 ISR guide, which says gateway DSP media resources communicate with Unified CM over SCCP (disputed). Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Transcoding Configuration](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_transcoding.html), Transcoding Configuration / restrictions and LTI overview. Checked 2026-09-25.
[^6]: The default MRGL is always searched, and it is the last resort when neither the device MRGL nor the device pool MRGL has an available resource, or when no MRGL is configured. 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), Background Information / Default MRGL. Checked 2026-09-25.
[^7]: A media resource that belongs to no media resource group is automatically part of the default MRGL. 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), Background Information / Default MRGL. Checked 2026-09-25.
[^8]: By default an individual device uses the media resources assigned to the device pool that it is in. 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), Media Resource Group Lists (overview). Checked 2026-09-25.
[^9]: When a device has an MRGL on the device and another on its device pool, Unified CM searches the device-level MRGL first and then the device pool MRGL. 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), Background Information / MRGL search order. Checked 2026-09-25.
[^10]: DSPs on IOS XE gateways can serve as media resources for transrating or transcoding, and each such media resource communicates with Unified CM using (Secure) SCCP. Source: [Cisco 4000 Series ISRs Software Configuration Guide, Cisco IOS XE Gibraltar 16.12.x - Configuring Voice Functionality](https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-12/isr4400swcfg-xe-16-12-book/configuring_voice_functionality.html), TLS 1.2 support on SCCP Gateways. Checked 2026-09-25.
[^11]: In Release 15, whether a call fails when no MTP or TRP can be allocated depends on the service parameters Fail Call If MTP Allocation Fails and Fail Call If Trusted Relay Point Allocation Fails. When these are not enabled, the call proceeds without the resource. 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), Media Termination Points / Trusted Relay Point (allocation failure behavior). Checked 2026-09-25.
[^12]: Activating the Cisco IP Voice Media Streaming service enables the annunciator, IVR, MTP, software conference bridge and music on hold resources on Unified CM. 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), Activate Software Media Resources. Checked 2026-09-25.
[^13]: The ISR 4000 software MTP restrictions include no hardware MTP for repacketization, no per-call debugging, no call threshold for standalone software MTP, and no RSVP agent. Source: [Cisco 4000 Series ISRs Software Configuration Guide, Cisco IOS XE Everest 16.6 - Support for Software Media Termination Point](https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-6/isr4400swcfg-xe-16-6-book/isr4400swcfg-xe-16-6-book_chapter_010110.html), Restrictions for Software Media Termination Point. Checked 2026-09-25.
[^14]: The ISR 4000 software MTP bridges media between two connections so Unified CM can relay calls routed through SIP or H.323 endpoints. It registers with Unified CM over SCCP, and its capacity is set with the maximum sessions software command. Source: [Cisco 4000 Series ISRs Software Configuration Guide, Cisco IOS XE Everest 16.6 - Support for Software Media Termination Point](https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-6/isr4400swcfg-xe-16-6-book/isr4400swcfg-xe-16-6-book_chapter_010110.html), Support for Software Media Termination Point / feature information and configuration. Checked 2026-09-25.
[^15]: For the ISR 4000 software MTP to work, the codec and packetization must be configured identically on the inbound and outbound call legs. Source: [Cisco 4000 Series ISRs Software Configuration Guide, Cisco IOS XE Everest 16.6 - Support for Software Media Termination Point](https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-6/isr4400swcfg-xe-16-6-book/isr4400swcfg-xe-16-6-book_chapter_010110.html), Support for Software Media Termination Point / Restrictions. Checked 2026-09-25.
[^16]: The IVR device lets Unified CM play prerecorded feature announcements, and by default an IVR supports 48 simultaneous callers. 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), Interactive Voice Response (overview). Checked 2026-09-25.
[^17]: LTI-based transcoding on CUBE reaches DSP resources through an internal API. It needs no TCP socket or registration, only a DSPFARM profile associated with application type CUBE. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Transcoding Configuration](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_transcoding.html), LTI-Based Transcoding. Checked 2026-09-25.
[^18]: Up to 501 MOH audio sources, numbered 1 to 501, can be configured. The fixed MOH device uses source 51. 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), Music On Hold audio sources / fixed MOH device. Checked 2026-09-25.
[^19]: Unified CM MOH supports the G.711 mu-law, G.711 a-law, G.729 and L16 256K wideband codecs. 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), Music On Hold / supported codecs. Checked 2026-09-25.
[^20]: When the Cisco IP Voice Media Streaming Application runs on a dedicated server on the 7500 or 10K OVA, the MOH guide states capacity of 1000 held callers, 500 MOH sources, and 300 to 700 annunciator callers, with one MOH codec. 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), Music On Hold / server capacity notes. Checked 2026-09-25.
[^21]: Cisco warns that the G.729a codec may not give acceptable audio quality for music. 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), Music On Hold Restrictions. Checked 2026-09-25.
[^22]: The held party's MRGL determines which MOH resource Unified CM allocates, using the device MRGL or, if the device has none, the device pool MRGL. 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), Music On Hold Overview / MOH resource selection. Checked 2026-09-25.
[^23]: User hold is invoked when a user presses the Hold button or softkey. Network hold is invoked automatically when a user activates Transfer, Conference or Call Park. 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), Music On Hold Overview / hold types. Checked 2026-09-25.
[^24]: Multicast MOH supports IPv4 only. 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), Music On Hold Restrictions. Checked 2026-09-25.
[^25]: For multicast MOH, the media resource group must include an MOH server set up for multicast, and the Use Multicast for MOH Audio check box must be checked on that group. 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), Multicast Music On Hold configuration / media resource groups. Checked 2026-09-25.
[^26]: An MOH server can transcode among the G.711 mu-law, G.711 a-law and L16 256K wideband MOH codecs, but it cannot transcode for G.729. 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), Music On Hold / codec and transcoding notes. Checked 2026-09-25.
[^27]: CTI devices and MTP devices do not support 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), Music On Hold Restrictions. Checked 2026-09-25.
[^28]: The Cisco IP Voice Media Streaming Application service must be activated to enable 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), Music On Hold Prerequisites / Configuration Task Flow. Checked 2026-09-25.
[^29]: If an MOH server fails during an active MOH session, the held party hears no music from then on, but normal call functions are not affected. 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), Music On Hold failover / restrictions. Checked 2026-09-25.
[^30]: For caller-specific MOH, if the user and network MOH audio source identifiers are not provisioned, the caller-specific MOH information in the SIP header is ignored and the call reverts to tone 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), Caller-Specific Music On Hold restrictions / Provisioning. Checked 2026-09-25.
[^31]: Unicast MOH streams go directly from the MOH server to the requesting endpoint. Multicast MOH streams go to a multicast group IP address, which endpoints join as needed. 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), Unicast and Multicast Music On Hold. Checked 2026-09-25.
[^32]: Unified CM uses a media resource from the next MRG in the same MRGL only after every resource in the current MRG is exhausted. 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), Background Information / MRGL behavior. Checked 2026-09-25.
[^33]: All resources in one MRG are treated as equal, and Unified CM shares load among the resources of each type in that MRG. 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), Background Information / MRG behavior. Checked 2026-09-25.
[^34]: A media resource group can contain annunciators, IVRs, conference bridges, MTPs, MOH servers and transcoders. 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), Media Resource Groups (overview). Checked 2026-09-25.
[^35]: Media resources become available to calls by being placed in a media resource group list (MRGL), which is then assigned to a device pool or to an individual device. 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), Media Resource Group Lists (overview). Checked 2026-09-25.
[^36]: An MRGL is a prioritized list of media resource groups, and resources are selected from the available groups in the priority order defined in the list. 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), Media Resource Group Lists (overview). Checked 2026-09-25.
[^37]: If an MTP is needed only for DTMF, Early Offer or IPv4/IPv6 conversion and both legs use the same codec and packetization, a software MTP (Unified CM IPVMS or ISR software MTP) is likely sufficient. If codecs differ, a DSP transcoder is likely needed (inferred). Source: [Cisco 4000 Series ISRs Software Configuration Guide, Cisco IOS XE Everest 16.6 - Support for Software Media Termination Point](https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-6/isr4400swcfg-xe-16-6-book/isr4400swcfg-xe-16-6-book_chapter_010110.html), Restrictions for Software Media Termination Point (combined with Release 15 Transcoders overview). Checked 2026-09-25.
[^38]: When a call leaves through a gateway and needs an MTP, the MTP is selected from the gateway's MRGL. 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), Which MRGL is used / MTP. Checked 2026-09-25.
[^39]: Neither the system's users nor the endpoint on whose behalf an MTP was inserted can see that the MTP is in use. 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), Media Termination Points (overview). Checked 2026-09-25.
[^40]: When Unified CM determines that a call endpoint requires an MTP, it allocates the resource from the MTP that has the fewest 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), Media Termination Points (overview). Checked 2026-09-25.
[^41]: One use that Unified CM 15 lists for an MTP is resolving mismatches in DTMF transport between call legs. 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), Media Termination Points (list of MTP uses). Checked 2026-09-25.
[^42]: One use that Unified CM 15 lists for an MTP is delivering SIP Early Offer over SIP trunks. 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), Media Termination Points (list of MTP uses). Checked 2026-09-25.
[^43]: For H.323 supplementary services, an MTP is required only for endpoints that support neither Empty Capability Set (ECS) nor FastStart. 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), Media Termination Points (list of MTP uses). Checked 2026-09-25.
[^44]: One use that Unified CM 15 lists for an MTP is converting RTP streams between IPv4 and IPv6. 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), Media Termination Points (list of MTP uses). Checked 2026-09-25.
[^45]: Cisco's MTP tech note says an MTP device may be allocated because of DTMF or RSVP requirements. Source: [Configure Media Termination Point](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/200613-Configure-Media-Termination-Point.html), Background Information. Checked 2026-09-25.
[^46]: The Release 15 guide names three MTP implementations: software MTPs in IOS gateways, hardware MTPs in IOS gateways, and the software MTP provided by the Cisco IP Voice Media Streaming service. 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), Media Termination Points (MTP types). Checked 2026-09-25.
[^47]: The Release 12.5(1) guide says that if no MTP resource is available when one is needed, the call connects without an MTP and has no supplementary services. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 12.5(1) - Configure Transcoders and Media Termination Points](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/12_5_1/systemConfig/cucm_b_system-configuration-guide-1251/cucm_b_system-configuration-guide-1251_chapter_01000010.html), Media Termination Points (overview). Checked 2026-09-25.
[^48]: Unified CM's own software media service probably cannot transcode, so codec conversion such as G.711 to G.729 likely needs a DSP-based transcoder in an IOS or IOS XE gateway (inferred). 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), Activate Software Media Resources; Transcoders (transcoder types). Checked 2026-09-25.
[^49]: PVDM4 modules support Opus transcoding for CUBE LTI-based transcoding. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Transcoding Configuration](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_transcoding.html), Transcoding Configuration / Opus. Checked 2026-09-25.
[^50]: The Unified CM 15 media resource types are annunciators, interactive voice response (IVR), media termination points (MTP), transcoders, trusted relay points, conference bridges, and music on hold/video on hold. 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), Media Resources Overview. Checked 2026-09-25.
[^51]: A software conference bridge supports up to 256 callers. At that setting it can host 64 four-party conference sessions. 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), Conference Bridge Types / Cisco Conference Bridge Software. Checked 2026-09-25.
[^52]: Software conference bridge 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), Conference Bridge Types / Cisco Conference Bridge Software. Checked 2026-09-25.
[^53]: The software conference bridge mixes audio with a simple summing algorithm, which can cause poor audio quality and low volume when a conference has many 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), Conference Bridge Types / Cisco Conference Bridge Software. Checked 2026-09-25.
[^54]: On a 10-Mb network or NIC, the Unified CM software MTP can provide approximately 24 MTP resources. 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), Media Termination Points (Cisco Media Termination Point Software). Checked 2026-09-25.
[^55]: The Cisco Media Termination Point Software type provides 48 MTP resources by default, and the number can be changed. 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), Media Termination Points (Cisco Media Termination Point Software). Checked 2026-09-25.
[^56]: The Release 15 media resources task flow activates software media resources (the Cisco IP Voice Media Streaming service) first. It then configures MTPs, transcoders, IVR and the annunciator, then media resource groups, then MRGLs, and then assigns them to a device or device pool. Announcements are optional later steps. 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), Media Resources Configuration Task Flow. Checked 2026-09-25.
[^57]: A transcoder converts an input stream in one codec into an output stream in a different codec. Unified CM inserts a transcoder when a call's endpoints use different voice codecs. 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), Transcoders (overview). Checked 2026-09-25.
[^58]: When a call needs both transcoding and MTP functions, Unified CM allocates a transcoder, because a transcoder can provide both functions at the same time. 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), Transcoders (overview). Checked 2026-09-25.
[^59]: The transcoder types listed in the Release 15 guide are Cisco Media Termination Point Hardware, Cisco IOS Media Termination Point (hardware), Cisco IOS Enhanced Media Termination Point (hardware) and Cisco Media Termination Point (WS-SVC-CMM). All are hardware types. 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), Transcoders (transcoder types). Checked 2026-09-25.
[^60]: A Trusted Relay Point (TRP) is an MTP or transcoder that Unified CM can insert into the media stream. A transcoder is made available as a TRP by checking the Trusted Relay Point 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), Trusted Relay Point (overview). Checked 2026-09-25.