For more information about RTP, check out these websites.

rfc.sunsite.dk/rfc/rfc1889.html
www.cs.columbia.edu/~hgs/rtp/faq.html
www-sop.inria.fr/rodeo/personnel/bolot/interop/rtp.html
searchnetworking.techtarget.com/sDefinition/0,,sid7_gci812019,00.html
icapeople.epfl.ch/thiran/CoursED/RTP.pdf