RTP and Reliability Real time media transfer requires high network throughput. Large delays need to be avoided, so eliminating data loss is less important than maintaining a constant data stream. The overhead of guaranteeing reliable transmission would slow the overall transmission rate. For this reason, the unreliable underlying protocol UDP is used, rather than reliable TCP, and RTP does not offer any reliability of flow and congestion control. There is no guarantee that the packets will be received in order, or without packet loss. When application appropriate, application-level framing can add a degree of reliability or flow and congestion control.