Hi Kiran,
BigBlueButton can access a webcam that is made available to on the host OS to applications.
For example, any webcam that registers itself as a DirectShow device is available for Windows Movie Maker, Skype, BigBlueButton, and etc.
If your webcam is only accessible via an IP address, then it's not visible to the operating system (and therefore not visible to apps running on the operating system).
Are you a developer? You could look at the RSP protocol and try using a tool such as ffmpeg to connect to your IP camera and, in turn, use ffmpeg to stream the video to red5 (via rtmp). There would be some learning involved as there is no out-of-the-box solution.
Another approach would be to see if your webcam provider has a software driver that would setup the remote IP webcam as another webcam for the host OS.
Regards,... Fred