McDewey

Quality of Service for Voice over IP IP RTP Header Compression 16 QoSVoIP.mif IP RTP Header Compression IP RTP header compression reduces the 40 byte IP+UDP+RTP header to 2 to 4 bytes, thereby reducing the bandwidth required per voice call on point-to-point links. The header is compressed at one end of the link and decompressed at the other end. Another standard name for this technique is cRTP, which stands for compressed RTP. Figure 4 shows the functionality of RTP header compression. Figure 4 RTP Header Compression To configure IP RTP header compression, you need to configure the ip rtp header-compression command under the serial interface, or the frame-relay ip rtp header-compression command under the Frame Relay subinterface. You can also configure the ip rtp compression-connections interface configuration command to set a maximum number of flows that will be compressed. Because cRTP can be processor intensive, you need to limit the number of compressed flows to prevent router performance degradation. Compressed RTP is recommended on low speed links where bandwidth is scarce and there are few VoIP calls. IP 20 UDP RTP IP Data 8 12 5 IP Data FTP SOL 1500 Byte -2.3% 256 Byte -13% VoIP Efficiencies 20 Byte -240% Payload Packet Size Reduction* *Also -5ms Reduction in Serialization Delay at 64 kbps RTP Compression Transmit Queue Output Hardware Configured Queuing (e.g. WFQ, CQ) Traffic Destined for Interface Identify RTP Traffic Compress RTP Traffic (Video, Audio, etc.) Classify Non-RTP Traffic 24174