CABLE MSOs

The cable industry has defined specifications to enable cable Multiple System Operators (MSOs) to deliver voice services in addition to their existing video and data services, over the same network infrastructure. Media servers are an integral part of the service platform for these services.

There are two industry organizations promoting and driving VoIP standards for the cable industry: for North America, CableLabs and their PacketCable project (www.cablelabs.org, www.packetcable.com); and for the rest of the world, IPCableCom, a project of the ITU-T (www.itu.int/itudoc/itu-t/com9/ipcable/).

The network reference model, shown above, includes a Call Management Server (CMS) for call and service control, a Media Terminal Adapter (MTA), various types of media gateways, and a media server. (The other components in the reference model do not interact directly with the media server.) The cable VoIP specifications use the terms "announcement server", "audio server", or "media player" for the media server.

The media server protocol specifications define the architecture and protocols that are required for the media server in Voice over IP (VoIP) cable networks. The functionality defined for the media server includes announcements, interactive voice response (IVR), and recording/playback. Future extensions will include conferencing, speech recognition, text-to-speech, and other capabilities.

The Call Management Server (CMS), which offers services such as Class 5 residential and voicemail service, controls the media server through the Network Call Signaling (NCS) protocol, which is similar to MGCP, or Megaco. Through this control interface the CMS instructs the media server to perform actions such as playing announcements and collecting digits, as required by the features running in the CMS.

The voice services delivered by the CMS make use of a media server for processing of audio streams. Here are some examples of how each of the media server's capabilities—also called building blocks—are used by the services:

• announcements: network announcements, service announcements for all services, branding
• IVR: feature programming, feature invocation, voicemail
• bridging: three-way calls
• play/record: call screening, voicemail
• speech recognition, text-to-speech: operator services, directory services, call center

Note that multiple CMSs and application servers, which are not shown in the diagram, can control the same media server through any mix of control protocols such as NCS and Megaco. Also, the media servers can be deployed at the edge of the network, in the core of the network, or in a combination of the two, depending on factors such as traffic volume and the cost of carrying traffic across the network.