SIP Based Multimedia Conferencing

I am looking for a complete Video Conferencing solution based on **SIP (Session Initiation Protocol)** and developed purely in **.Net** (preferably in VB.Net). There are already a few products of multimedia conferencing based on H.32x standard. But SIP, which is a more feasible protocol, is put on the agenda of being the call signaling protocol for conferencing. The goal of the project is to implement a Video Conferencing service using SIP protocol that not only guarantees better real time service, but also gives better performance with respect to the playback of the streamed media data. Once the implementation of video conferencing part is complete, enough information will be available regarding the type of conferencing that a user does and with which user does he/she interacts most of the time. So, mining structures is to be added to the project using SQL Server 2008. A mining structure will give detailed information about the user, what kind of conferencing he/she does and with which user he/she interacts most of the time. So next time whenever a particular user logins, database should be searched and a popup should come asking if the user wants to do a voice chat or video chat and with which user etc etc.. I came across a solution named **'1VideoConference'**. People interested in this project can google it and see the features. Its features are exactly the same that I am looking for. But I doubt if it works on SIP. My system should not use the H.263 protocol at any cost. Instead it should work purely on SIP protocol. Please revert back as soon as possible.