RTP header compression is a mechanism that routers use to reduce 40 bytes of protocol overhead to approximately 2 to 4 bytes. Cisco routers uses this RTP header compression. The RTP header compression can drastically reduce the IP telephony bandwidth consumption on a WAN link when using 20 ms G.729 audio. When the combined 40 byte header is reduced to 4 bytes, the total IP packet size is reduced by 60% (from 60 bytes to 24 bytes). This equates to reducing the total IP telephony WAN bandwidth consumption by roughly half, and it applies to all 20 ms G.729 audio packets, regardless of the vendor.