Real-Time Transport Protocol (RTP) can help achieve interoperability among different implementations of network audio and video applications. However, the header can be too large a payload for networks using low-speed lines such as dial-up modems. Compressed Real-Time Transport Protocol (CRTP) can reduce network overhead on a low-speed link. On a J-series device, CRTP can operate on a T1 or E1 interface with PPP encapsulation.