How to develop real-time communication program through RTP

[AntonlioX]

Recently I have read some materials on RTP ,But I still could not know how to realize it ? Can anybody tell me some advice . I have known the RTP/RTCP packet structure ,but I don't know how to fill the structure ,for I wonder how to get the original data used to fill in the stucture ,which I guessed is realized by myself not the RTP protocol. AntonlioX