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Collaboration, Voice & AV · Advanced

Compressed Real-time Transport Protocol (cRTP)

Header compression that reduces the 40-byte IP/UDP/RTP header to 2 to 4 bytes on slow point-to-point WAN links.

Definition

cRTP (RFC 2508) works hop by hop by sending only changes to header fields that stay mostly constant within a flow. It dramatically lowers bandwidth for compressed codecs such as G.729, where headers are larger than the payload, but it consumes router CPU and is only practical on slow serial links. It is configured per interface and must be enabled on both ends of the link.

Example

ip rtp header-compression on a 256 kbps serial link reduces a G.729 call from about 24 kbps to about 12 kbps.

Exam tip

cRTP helps most with small payloads on slow links; it is hop by hop, not end to end.

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