Why Does RTP use UDP instead of TCP?

Question

I wanted to know why UDP is used in RTP rather than TCP ?. Major VoIP Tools used only UDP as i hacked some of the VoIP OSS.

Answer 1

UDP is used wherever data is send, that does not need to be exactly received on the target, or where no stable connection is needed.

TCP is used if data needs to be exactly received, bit for bit, no loss of bits.

For Video and Sound streaming, some bits that are lost on the way do not affect the result in a way, that is mentionable, some pixels failing in a picture of a stream, nothing that affects a user, on DVDs the lost bit rate is higher.