Avaya X330WAN manual RTP Header Compression cRTP

RTP Header Compression (cRTP)

RTP Header Compression (cRTP)

Real Time Protocol (RTP) is the basis of common VoIP traffic. RTP runs over UDP, and incurs a 12-byte header on top of other (IP, UDP) headers. Running on PPP or Frame-Relay, this protocol can be compressed.

The X330WAN RTP Header Compression process is based on the following facts:

•The packet order on a PPP and Frame Relay link is preserved.

•After transmitting full headers usually only the “deltas” from the full packet’s header need to be sent, and not the full header itself. This is due to the IP, UDP, and RTP header structure.

•Since the “deltas” are often constant, the second order “delta” is then 0 and does not need to be transmitted.

You can configure how often the full header is transmitted, either as a function of time or transmitted compressed packets.

RTP Header Compression can reduce the size of all three headers (IP+UDP+RTP~40 bytes) to 2-4 bytes.

X330WAN can compress only RTP packets. Any UDP packet with an even destination port within a user-configurable range of ports, is considered an RTP packet.

X330WAN can decompress any type of compressed packets. Decompression is enabled whenever the RTP compression is enabled. By default, X330WAN decompresses up to 16 compressed TCP connections. You can modify this number (within the range of 3-256) using the ip tcp decompression-connectionscommand.

Note: When the device on the other end is a non-Avaya device:

-Configure the port range of the Avaya device to 49152 - 65535 using the ip rtp port-rangecommand. Ensure that your voice application (i.e., the Avaya DEFINITY Communication Server) is using the same port range.

-Configure the maximum number of connections to 255 using the ip rtp compression-connectionscommand.

-Verify that you are working in the non-ietfworking mode. This mode is the default cRTP operational mode of X330WAN. You can change this mode using the ip rtp non-tcp mode command.

Avaya X330WAN User’s Guide 53