Cisco Systems 3600 manual Configure RTP Header Compression, Multilink PPP Configuration Example

Configure IP Networks for Real-Time Voice Traffic

For more information about Multilink PPP, refer to the “Configuring Media-Independent PPP and Multilink PPP” chapter in the Dial Solutions Configuration Guide.

Multilink PPP Configuration Example

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:

interface virtual-template 1

pppmultilink encapsulated ppp

ppp multilink interleave

ppp multilink fragment-delay 20 ip rtp reserve 16384 100 64

multilink virtual-template 1

Configure RTP Header Compression

Real-Time Transport Protocol (RTP) is used for carrying packetized audio traffic over an IP network. RTP header compression compresses the IP/UDP/RTP header in an RTP data packet from 40 bytes to approximately 2 to 4 bytes (most of the time), as shown in Figure 4.

This compression feature is beneficial if you are running Voice over IP 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).

Figure 4 RTP Header Compression

VC-20Voice, Video, and Home Applications Configuration Guide