Table Of Contents

Transcoders

Understanding Transcoders

Managing Transcoders with the Media Resource Manager

Transcoder Capacity

Using Transcoders as MTPs

Transcoder Failover and Failback

Active Cisco CallManager Becomes Inactive

Resetting Registered Transcoder Devices

Dependency Records

Transcoder Configuration Checklist

Where to Find More Information

Transcoders

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The Media Resource Manager (MRM) provides resource registration and resource reservation of transcoders within a Cisco CallManager cluster. Cisco CallManager supports simultaneous registration of both the MTP and transcoder and concurrent MTP and transcoder functionality within a single call.

This section covers the following topics:

•Understanding Transcoders

•Managing Transcoders with the Media Resource Manager

•Transcoder Capacity

•Using Transcoders as MTPs

•Transcoder Failover and Failback

•Dependency Records

•Transcoder Configuration Checklist

•Where to Find More Information

Understanding Transcoders

A transcoder takes the output stream of one codec and transcodes (converts) it from one compression type to another compression type. For example, it could take an output stream from a G.711 codec and transcode (convert) it in real time to a G.729 input stream. In addition, a transcoder provides MTP capabilities and may be used to enable supplementary services for H.323 endpoints when required.

The Cisco CallManager invokes a transcoder on behalf of endpoint devices when the two devices use different codecs and would normally not be able to communicate. When inserted into a call, the transcoder converts the data streams between the two incompatible codecs to enable communications between them.

A transcoder requires specific hardware to run. The same hardware also supports conference bridges, transcoders, or public rate interface/channel associated signaling (PRI/CAS) interfaces.

A transcoder provides a designated number of streaming mechanisms, each of which can transcode data streams between different codecs and enable supplementary services, if required, for calls to H.323 endpoints.

Managing Transcoders with the Media Resource Manager

All Cisco CallManagers within a cluster can access transcoders through the Media Resource Manager (MRM). The MRM manages access to transcoders.

The MRM makes use of Cisco CallManager media resource groups and media resource group lists. The media resource group list allows transcoders to communicate with other devices in the assigned media resource group, which in turn, provides management of resources within a cluster.

A transcoder control process gets created for each transcoder device that is defined in the database. Each transcoder registers with the MRM when it initializes. The MRM keeps track of the transcoder resources and advertises their availability throughout the cluster.

Transcoder Capacity

The maximum transcoding sessions per port specifies 24. The following list provides the supported transcoding capacity and sessions per port:

•G711-G711 MTP: 24 (no DSP is involved)

•G729-G729 MTP: 24 (no DSP is involved)

•G711-G723 transcoding: 24

•G711-G729 transcoding: 24

•G711-GSM Full Rate (FR) transcoding: 24

•G711-GSM Enhanced Full Rate (EFR) transcoding: 24

For example, consider that transcoder 1 is configured for 24 transcoder resources, and transcoder 2 is also configured for 24 transcoder resources. If both transcoders register with the same Cisco CallManager, that Cisco CallManager maintains both sets of resources for a total of 48 registered transcoder resources.

The basis for the capacity of 24 transcoders represents a packet size of 1 packet per 20 msec. The smaller packet size of 10 msec does not increase audio quality. Rather, it reduces the total capacity of transcoder resources.

When the Cisco CallManager determines that the two endpoints of a call are using different codecs and cannot communicate directly, it inserts a transcoder into the call to transcode the datastreams between them. The transcoder remains invisible to either the user or the endpoints that are involved in a call.

Using Transcoders as MTPs

The CAT6000 WS-X6608-T1/E1 transcoder port resources also support MTP functionality to enable supplementary services for H.323 endpoints if no software MTP is available within the Cisco CallManager cluster. In this capacity, when the Cisco CallManager determines that an endpoint in a call requires an MTP, it allocates a transcoder resource and inserts it into the call, where it acts like an MTP transcoder.

Cisco CallManager supports MTP and transcoding functionality simultaneously. For example, if a call originates from a Cisco IP Phone (located in the G723 region) to NetMeeting (located in the G711 region), one transcoder resource supports MTP and transcoding functionality simultaneously.

If a software MTP/transcoder resource is not available when it is needed, the call connects without using a transcoder resource, and that call does not have supplementary services. If hardware transcoder functionality is required (to convert one codec to another) and a transcoder is not available, the call will fail.

Transcoder Failover and Failback

This section describes how transcoder devices failover and failback when the Cisco CallManager to which they are registered becomes unreachable. The section also explains conditions that can affect calls that are associated with a transcoder device, such as transcoder 1 reset or restart.

Related Topics

•Active Cisco CallManager Becomes Inactive

•Resetting Registered Transcoder Devices

Active Cisco CallManager Becomes Inactive

The following items describe the MTP device recovery methods when the MTP is registered to a Cisco CallManager that goes inactive:

•If the primary Cisco CallManager fails, the transcoder attempts to register with the next available Cisco CallManager in the Cisco CallManager Group that is specified for the device pool to which the transcoder belongs.

•The transcoder device reregisters with the primary Cisco CallManager as soon as it becomes available after a failure and is currently not in use.

•A transcoder device unregisters with a Cisco CallManager that becomes unreachable. The calls or conferences that were on that Cisco CallManager will register with the next Cisco CallManager in the list.

•If a transcoder attempts to register with a new Cisco CallManager and the register acknowledgment is never received, the transcoder registers with the next Cisco CallManager.

Resetting Registered Transcoder Devices

The transcoder devices will unregister and then disconnect after a hard or soft reset. After the reset completes, the devices reregister with the primary Cisco CallManager.

Dependency Records

To find out which media resources are associated with a transcoder, click the Dependency Records link that is provided on the Cisco CallManager Administration Transcoder Configuration window. The Dependency Records Summary window displays information about media resource groups that are using the transcoder. To find out more information about the media resource group, click the media resource group and the Dependency Records Details window displays.

For more information about Dependency Records, refer to Accessing Dependency Records in the Cisco CallManager Administration Guide.

Transcoder Configuration Checklist

Table 18-1 provides a checklist to configure transcoders.

Table 18-1 Transcoder Configuration Checklist 

Configuration Steps		Procedures and Related Topics
Step 1	Determine the number of transcoder resources that are needed and the number of transcoder devices that are needed to provide these resources.	Transcoder Configuration, Cisco CallManager Administration Guide
Step 2	Add and configure the transcoders.	Transcoder Configuration, Cisco CallManager Administration Guide
Step 3	Add the new transcoders to the appropriate media resource groups.	Media Resource Management, page 16-1 Media Resource Group Configuration Settings, Cisco CallManager Administration Guide
Step 4	Restart the transcoder device.	Resetting a Transcoder, Cisco CallManager Administration Guide

Where to Find More Information

Related Topics

•Cisco IP Voice Media Streaming Application

•Media Resource Management, page 16-1

•Media Termination Points, page 20-1

•Media Resource Group Configuration, Cisco CallManager Administration Guide

•Media Resource Group Configuration Settings, Cisco CallManager Administration Guide

Additional Cisco Documentation

•Cisco IP Telephony Network Design Guide