Planning Media Resources for Your VoIP Environment

Author: Bernie Gardiner

Abstract

Media Resource design is an important component of overall IP Telephony implementations. Media resources are software- or hardware-based components that perform processing on two or more connected media streams. Care must be taken to ensure that resources are available at the right locations for maximum link efficiency. With proper planning and configuration, devices will rely on local resources without placing an unnecessary load on WAN links.

Introduction

Media resources are software- or hardware-based components that perform processing on two or more connected media streams. The following functions can be performed by media resources in your environment.

• Voice Termination - The ability to connect an IP call leg to a non-IP call leg such as a TDM connection. A voice gateway with a connection to the PSTN or PBX provides voice termination capabilities.
• Conferencing - The ability to connect multiple IP call legs, mix the participant streams, and create a composite stream to send back to each participant. Cisco Unified Communications Manager (CUCM), a voice gateway, or any conference bridge can provide conferencing capabilities.
• Transcoding - The ability to translate a stream encoded by one codec into a stream encoded by a different codec. A voice gateway can provide transcoding capabilities.
• Media Termination Point (MTP) - A component that bridges two streams with different characteristics and controls each stream independent of the other. MTP functions may include bridging two streams that use different packetization periods, support for different supplementary service capabilities, or bridging different DTMF Relay capabilities. A voice gateway or CUCM can provide MTP capabilities.
• Music on Hold (MoH) - A feature that provides music to callers when they are placed on hold, transferred, parked, or added into an ad-hoc conference. A voice gateway or CUCM can provide MoH capabilities. Music sources, either from a file or a live feed, must also be configured in CUCM.
• Annunciator - A feature that provides spoken messages or progress tones from the CUCM system to the end user. This is the only feature that is provided solely by CUCM and cannot be provisioned on an external gateway.

Software-based resources are enabled on CUCM by activating the IP Voice Media Streaming Application on one or more CUCM servers in a cluster. Enabling this application automatically provides software-based support for MoH, software-based Conference Bridge, MTP, and Annunciator services. The Annunciator service is the only service that must be provisioned through the CUCM IP Voice Media Streaming Application. Conference Bridging and MTP can be provisioned either through the CUCM IP Voice Media Streaming Application as software-based resources or through external servers or gateways as hardware-based resources. Transcoding is done using DSPs (digital signal processors), and MoH can be provided by CUCM or a router with a local music source file and appropriate configuration.

Hardware-based resources are provided by DSP that typically reside in voice gateways or voice capable modules.

In some chassis, DSPs are associated with voice network modules and by default are provisioned to support voice termination for those voice-capable interfaces. If not, all interfaces will be used for voice termination. These DSPs can be reconfigured to provide support for other media resource requirements, such as Conferencing, MTP, and Transcoding. DSP farms and profiles are configured, and these resources are registered with a CUCM cluster.

In other chassis, DSP resources are resident on the motherboard instead of residing on voice network modules. These DSP resources can be configured to support voice termination as well as Conferencing, MTP, and Transcoding. Voice termination and transcoding (beyond alaw to ulaw conversion) can only be done on a hardware resource.

The media resource challenge in any Voice over IP (VoIP) environment is to determine what resources are needed to support calling requirements and to control which resources should be accessible to which devices. The planning strategy must include calculating the following.

• Number of concurrent calls for voice termination requirements
• Number of conferences and participants
• Types of conferences: single mode or mixed mode
• Number of transcoding sessions required
• Types of transcoding: alaw-ulaw or G.711-G.729, etc.
• Number of MoH servers
• Types of MoH: unicast or multicast
• Number of MTP sessions required
• Number of Annunciator sessions required
• Number of DSPs to support calling requirements

The resulting configurations will include the following.

• Activation of IP Voice Media Streaming Application on CUCM(s)
• Configuration of DSP farms and DSP Profiles on voice gateways
• Configuration for support of SCCP on voice gateway
• Configuration of Media Resource Services on CUCM
• Configuration of Media Resource Groups and Media Resource Group Lists on CUCM
• Assignment of Media Resource Group Lists to endpoints on CUCM

Each of these topics and associated configurations will be explored in further detail in this document.

Related Courses

CIPT1 - Cisco IP Telephony Part 1 v4.1
CIPT2 - Cisco IP Telephony Part 2 v4.1
CVOICE - Cisco Voice over IP v6.0