The Pulver people asked me to participate in the VON.x Spring 2008 panel, Redefining Hosted Media, which prompted me to think about some of the considerations a service provider needs to make when planning how a new service deployment will be implemented. One of the big benefits of new service architectures and software-only implementations is how a service network’s core can be either repurposed or extended at a very low cost compared with the initial buildout.

      What I intend to discuss on the panel is how a vendor may offer a network architecture that will do a fine job of implementing the current service, voice messaging, for example, but be unable to be extended to support voice-fax unified messaging if the original voice media server does not support fax…and most don’t.

     The central point of my presentation is that the service network should have third-party call control (3PCC) from the perspective of the gateway and the media servers, enabling the call to be moved from one media server to another as the caller’s responses and the application logic require. In a SIP service network, 3PCC requires a back-to-back user agent (B2BUA). A B2BUA, essentially a switch, mediates a call by maintaining call state for each of the two call legs, in this case the media-gateway and the media-server call legs. Since the B2BUA can, therefore, exert its will over both call legs, it’s free to move the call’s media stream from, for example, the voice-messaging media server to the fax media server when the application requires.

     But you can implement a voice-messaging system quite nicely without a 3PCC entity by routing all calls directly to the voice media server (where else?). The voice media server might include a VXML voice browser that accesses VXML scripts from a Web server. OK so far, but suppose the service provider wants to later add fax to his UM system and the voice media server does not support fax. You then have the need for the call’s media stream to be moved from the voice to the fax media server. Although the voice media server may be able to move the RTP stream through itself to the fax media server, what happens when the fax media server wants to REINVITE the gateway over to T.38? Ooops! Voice media servers don’t do this.

     Since the voice media server isn’t going to do it. You need…third-party call control!

     The point? Even though a service-network architecture may support today’s application, it might not support tomorrow’s. The IMS architecture is specifically designed to support service networks that have multiple application servers and multiple media servers. So, even if you don’t intend to acquire a full-up IMS network, consider using the basic IMS network architecture and you’ll enjoy many of the benefits. You can then layer in additional components as follow-on projects.

Thanks for your time, Mike Coffee CEO, Commetrex