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4-13
T1/E1 Digital Voice Port Adapter Installation and Configuration
OL-3592-02
Chapter 4 Configuring the PA-VXA, PA-VXB, and PA-VXC
Configuring Voice over IP
Figure 4-1
RTP Header Compression
You should configure RTP header compression if the following conditions exist in your network:
•
Slow links
•
Need to save bandwidth
Note
Do not use RTP header compression on links greater than 2 Mbps.
Perform the following tasks to configure RTP header compression for VoIP. The first task is required;
the second task is optional.
•
Enable RTP Header Compression on a Serial Interface, page 4-13
•
Change the Number of Header Compression Connections, page 4-14
Enable RTP Header Compression on a Serial Interface
To use RTP header compression, you need to enable compression on both ends of a serial connection.
To enable RTP header compression, use the following command in interface configuration mode:
ip rtp header-compression [passive]
If you include the passive keyword, the software compresses outgoing RTP packets only if incoming
RTP packets on the same interface are compressed. If you use the command without the passive
keyword, the software compresses all RTP traffic.
Before RTP header compression:
20 bytes
8 bytes
20 to 160 bytes
12 bytes
IP
Header
UDP
RTP
Payload
After RTP header compression:
2 to 4 bytes
20 to 160 bytes
IP/UDP/RTP header
Payload
12076