Media Termination Point Resources

Media Termination Points (MTPs) are used to extend supplementary services to H.323 endpoints that do not support the H.323 Version 2 (H.323v2) OpenLogicalChannel and CloseLogicalChannel request features with the EmptyCapabilitiesSet feature. Supplementary services are features such as:

• Call Hold
• Call Transfer
• Call Park
• Conferencing

An MTP is an entity that accepts two full-duplex G.711 streams. It bridges the media streams together and allows them to be set up and torn down independently. Simply put, the MTP allows a call to be held (maintained) when a user places it on hold due to one of the services mentioned previously. The streaming data received from the input stream on one connection is passed to the output stream on the other connection, and vice versa. In addition, the MTP transcodes G.711 a-law to G.711 mu-law, and vice versa, and adjusts packet sizes as required by the two connections.

When needed, an MTP is allocated and connected into a call on behalf of an H.323 endpoint. After being inserted, the media streams are connected between the MTP and the H.323 device, and these connections are present for the duration of the call. The media streams connected to the other side of the MTP can be connected and disconnected as needed to implement features such as hold, transfer, and so forth.

Cisco CallManager requires an RFC 2833 dual-tone multifrequency (DTMF)-compliant MTP device to make Session Initiation Protocol (SIP) calls. The current standard for SIP uses in-band payload types to indicate DTMF tones. Cisco components such as Skinny-based IP Phones support only out-of-band payload types. Thus, an RFC 2833-compliant MTP device monitors for payload type and acts as a translator between in-band and out-of-band payload types. With the MTP device, any service that requires a media change (such as call hold) happens transparently.

Table 15-3 provides additional detail about MTP resources.

MTP Configuration

By default, any Cisco CallManager software-based MTP resources are automatically added to the cluster when you have activated the Voice Media Streaming Application on a server. If you do not want a CallManager server to participate in MTP processing (which saves resources), delete the server from under the MTP Configuration window. Hardware-based MTP resources (known as Cisco IOS Enhanced Software Media Termination Points) must manually be added to the cluster.

To configure or add an MTP, choose Service > Media Resource > Media Termination Point from the Cisco CallManager Administration console and click Add a New Media Termination Point. The Media Termination Point Configuration window shown in Figure 15-2 appears.

Figure 15-2. Media Termination Point Configuration Window

From here, you can choose to add a software- or hardware-based conference bridge to the CallManager cluster configuration. Table 15-4 describes the configuration options available from this window.