Avaya X330WAN - Manual (Page 75)

RTP Header Compression (cRTP)
Avaya X330WAN User’s Guide 53
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-connections
command.
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-range command. 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-connections command.
- Verify that you are working in the non-ietf working mode. This mode is the
default cRTP operational mode of X330WAN. You can change this mode using
the
ip rtp non-tcp mode command.