Real-Time Transport Protocol (RTP) can help achieve interoperability among different implementations of network audio and video applications. However, in some cases, the header, which includes the IP, UDP, and RTP headers, can be too large (around 40 bytes) on networks using low-speed lines such as dial-up modems. Compressed Real-Time Transport Protocol (CRTP) can be configured to reduce network overhead on low-speed links. CRTP replaces the IP, UDP, and RTP headers with a 2-byte context ID (CID), reducing the header overhead considerably.
Figure 39 shows how CRTP compresses the RTP headers in a voice packet and reduces a 40-byte header to a 2-byte header.
Figure 39: CRTP
On Services Routers, you can configure CRTP with MLPPP or PPP logical interface encapsulation on link services interfaces. For more information about configuring MLPPP, see Configuring an MLPPP Bundle.
When you configure CRTP, link fragmentation and interleaving (LFI) is automatically enabled. Real-time and non-real-time data frames are carried together on lower-speed links without causing excessive delays to the real-time traffic. For more information about LFI, see Link Fragmentation and Interleaving Overview.