Media Resource Support

CUCM offers software-based media resources. Start the IP Voice Media Streaming application to activate the following:

■ Audio conferencing

■ Annunciator

The following media resources are available only in hardware:

■ Transcoding

■ Voice termination

Audio conferencing and MTP media resources can also be offered by hardware media resources. MoH is a special case. Because of the potential WAN bandwidth utilization of MoH, the multicast streams of the server are normally scoped at the headquarters. Survivable Remote Site Telephony (SRST) can stream one media resource at branch locations.

The signaling between hardware media resources and CUCM most often uses SCCP to set up and tear down calls. All audio streams from any endpoint are always terminated by the media resources involved in the call. There is no direct IP phone-to-IP phone audio stream with media resources involved in the call flow.

The voice-termination function is needed when an incoming or outgoing TDM call is terminated on a gateway. The TDM leg is terminated by the Cisco IOS router's DSP and has to perform decoding, coding, and packetization functions.

There are two different audio streams in Figure 15-1, one inside the public switched telephone network (PSTN), the other one a VoIP audio stream using RTP transport.

Signaling messages are exchanged between the gateway and CUCM and between the telephony device and CUCM. The PSTN signaling is not considered in Figure 15-1.

Figure 15-1 PSTN Voice Termination

Figure 15-1 PSTN Voice Termination

DSPs for Voice Termination

RTP bearer traffic streams are sent from the IP phones to the conference bridge resource mixing the audio. The conference resource mixes the audio streams and sends back a unique audio stream to the IP phones. The audio stream must subtract the audio stream of the person receiving the audio stream so that no echo is heard. Some conference devices, because of processing limitations, mix only the three loudest talkers.

Signaling messages (control traffic) are exchanged among the IP phones, CUCM, and the conferencing resource (if using a hardware resource or a version of Cisco Unified MeetingPlace). Cisco Unified MeetingPlace is not covered in this book.

NOTE The Cisco Press book Voice and Video Conferencing Fundamentals is an excellent resource for a more thorough understanding of audio conferencing and videoconferencing.

Most conference bridges that are under the control of CUCM use SCCP to communicate with CUCM. Session Initiation Protocol (SIP) support is increasingly being added to all the Unified Communications components.

CUCM does not distinguish between software- and hardware-based conference bridges when it processes a conference allocation request. Allocation of conferencing resources is covered in further detail later in this chapter. The number of individual conferences and maximum number of participants per conference varies based on the resource in use. Figure 15-2 illustrates that software conferencing is integrated into CUCM.

Figure 15-2 Software Conferencing

: - \ Integrated Conference Bridge

Conference Call

Figure 15-2 Software Conferencing

Conference Call

A transcoder converts an input audio stream using one audio codec into an output stream that uses a different audio codec. The transcoder in Figure 15-3 is implemented using DSP resources in the Cisco router. Transcoders are necessary when audio streams are using compressed audio codes (G.729 or iLBC), but the resource they are attempting to use accepts only G.711 calls. iLBC is the Internet Low Bandwidth Codec, which operates at 15.2 kbps. Most Cisco Unify voice-mail deployments use the G.711 audio codec for voice-mail storage to guarantee high quality.

Audio streams (RTP bearer channels) are set up between the telephony devices and the transcoder. Signaling messages are exchanged between the telephony devices and CUCM and between the transcoder resource and CUCM. DSP resources are required to perform transcoding. Those DSP resources are located in Cisco routers and switches.

Figure 15-3 Transcoding Media Resources

Figure 15-3 Transcoding Media Resources

Audio------Signaling

An MTP bridges two media streams and allows them to be set up and torn down independently.

An MTP can be used as an instance of translation between incompatible audio streams, to synchronize clocking, or to enable supplementary services for devices that do not support the empty capability set (ECS) option of the H.323 Version 2 protocol.

Audio streams exist between telephony devices and the MTP resource. Signaling messages are exchanged between the telephony devices and CUCM. Figure 15-4 illustrates a hardware-based MTP.

Figure 15-4 Hardware MTP

Figure 15-4 Hardware MTP

Audio------Signaling

An annunciator is a function of the Cisco IP Voice Media Streaming application service that provides the ability to stream spoken messages or various call-progress tones from the CUCM system to a user.

The annunciator can send multiple one-way RTP streams to devices such as Cisco IP Phones or gateways, using SCCP messages to set up the RTP stream. Tones and announcements are predefined by the system. The announcements support localization and may also be customized by replacing the appropriate WAV file. The annunciator can support G.711 a-law, G.711 mu-law, G.729, and Cisco wideband audio codecs without transcoding resources.

Signaling messages are exchanged between telephony devices and CUCM. The audio stream is one way, from the annunciator to the telephony device. The annunciator is a software component of CUCM, as shown in Figure 15-5.

The MoH feature is part of the Cisco IP Voice Media Streaming (IPVMS) service running on CUCM. This feature provides music to callers when their call is placed on hold or a supplementary service is initiated. Supplementary services are not limited to, but include the following: transfer, park, and conference. When a supplementary service is initiated, the call is temporarily put on hold before the function is completed. Implementing MoH is relatively simple but requires a basic understanding of IP unicast and multicast traffic, MoH call flows, configuration options, server behavior, and requirements.

Figure 15-5 Annunciator Services

Figure 15-5 Annunciator Services

Audio------Signaling

Audio streams are created between telephony devices and the MoH server. Signaling messages are exchanged between telephony devices and CUCM. Figure 15-6 illustrates the MoH component of CUCM.

Figure 15-6 Music on Hold

Integrated

Figure 15-6 Music on Hold

Integrated

Put Call Hold Cucm Cube Call Flow
Audio------Signaling

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