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Chapter 6
Configuring VoIP
Multilink PPP Configuration Example
Configure Real-Time Transport Protocol Header Compression
OL-2031-02
The following example defines a virtual interface template that enables multilink
PPP with interleaving and a maximum real-time traffic delay of 20 milliseconds,
and then applies that virtual template to the multilink PPP bundle:
c4224(config)# interface virtual-template 1
c4224(config-if)# ppp multilink
c4224(config-if)# encapsulated ppp
c4224(config-if)# ppp multilink interleave
c4224(config-if)# ppp multilink fragment-delay 20
c4224(config-if)# ip rtp reserve 16384 100 64
c4224(config)# multilink virtual-template 1
Real-Time Transport Protocol (RTP) is used for carrying audio traffic in packets
over an IP network. RTP header compression compresses the RTP/UDP/IP header
in an RTP data packet from 40 bytes to approximately 2 to 4 bytes, in most cases,
as shown in
Figure
6-1.
This compression feature is beneficial if you are running VoIP over slow links.
Enabling compression on both ends of a low-bandwidth serial link can greatly
reduce the network overhead if there is a lot of RTP traffic on that slow link.
Typically, an RTP packet has a payload of approximately 20 to 160 bytes for audio
applications that use compressed payloads. RTP header compression is especially
beneficial when the RTP payload size is small (for example, compressed audio
payloads between 20 and 50 bytes).
Catalyst 4224 Access Gateway Switch Software Configuration Guide
Configure IP Networks for Real-Time Voice Traffic
6-9
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Troubleshooting
