RTP session in SIP

Hello, I'm developing a project that transmit audio/video over the internet. We choose the JAIN-SIP and NIST stack, and we have nice SIP sessions, but how we establish the RTP Session (Media Session, you can suggest another protocol )????. I've seen that the JMF offers a way to transmit video with RTP but I can't figure out the way to integrate it with the SIP session.

Thanks,

Marcelo