Cisco Systems 3825 manual Passive Keyword, Iphc-format Keyword, Ietf-format Keyword

Appendix A Cisco 3825 Mobile Wireless Edge Router RAN-O Command Reference

ip rtp header-compression

The passive Keyword

By default, the ip rtp header-compressioncommand compresses outgoing RTP traffic. If you specify the passive keyword, outgoing RTP traffic is compressed only if incoming RTP traffic on the same interface is compressed. If you do not specify the passive keyword, all outgoing RTP traffic is compressed.

The passive keyword is ignored on PPP interfaces. PPP interfaces negotiate the use of header-compression, regardless of whether the passive keyword is specified. Therefore, on PPP interfaces, the passive keyword is replaced by the IPHC format, the default format for PPP interfaces.

The iphc-format Keyword

The iphc-formatkeyword indicates that the IPHC format of header compression that will be used. For

PPPand HDLC interfaces, when the iphc-formatkeyword is specified, TCP header compression is also enabled. For this reason, the ip tcp header-compressioncommand appears in the output of the show running-configcommand. Since both RTP header compression and TCP header compression are enabled, both UDP packets and TCP packets are compressed.

The iphc-formatkeyword includes checking whether the destination port number is even and is in the ranges of 16,385 to 32,767 (for Cisco audio) or 49,152 to 65,535 (for Cisco video). Valid RTP packets that meet the criteria (that is, the port number is even and is within the specified range) are compressed using the compressed RTP packet format. Otherwise, packets are compressed using the less-efficient compressed non-TCP packet format.

The iphc-formatkeyword is not available for interfaces that use Frame Relay encapsulation.

Note The header compression format (in this case, IPHC) must be the same at both ends of the network. That is, if you specify the iphc-formatkeyword on the local router, you must also specify the iphc-formatkeyword on the remote router.

The ietf-format Keyword

The ietf-formatkeyword indicates that the IETF format of header compression will be used. For HDLC interfaces, the ietf-formatkeyword compresses only UDP packets. For PPP interfaces, when the ietf-formatkeyword is specified, TCP header compression is also enabled. For this reason, the ip tcp header-compressioncommand appears in the output of the show running-configcommand. Since both RTP header compression and TCP header compression are enabled, both UDP packets and TCP packets are compressed.

With the ietf-formatkeyword, any even destination port number higher than 1024 can be used. Valid RTP packets that meet the criteria (that is, the port number is even and is higher than 1024) are compressed using the compressed RTP packet format. Otherwise, packets are compressed using the less-efficient compressed non-TCP packet format.

The ietf-formatkeyword is not available for interfaces that use Frame Relay encapsulation.

Note The header compression format (in this case, IETF) must be the same at both ends of the network. That is, if you specify the ietf-formatkeyword on the local router, you must also specify the ietf-formatkeyword on the remote router.

Support for Serial Lines

RTP header compression is supported on serial lines using Frame Relay, HDLC, or PPP encapsulation. You must enable compression on both ends of a serial connection.

	Cisco 3825 Mobile Wireless Edge Router Software Configuration Guide
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