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Configuring IP Networks for Real-Time Voice Traffic

Release 12.0(7)XK

Change the Number of Header Compression Connections

By default, the software supports a total of 32 RTP header compression connections on an interface.

To specify a different number of RTP header compression connections, use the following command

in interface conﬁguration mode:

RTP Header Compression Conﬁguration Example

The following example enables RTP header compression for a serial interface:

interface 0

ip rtp header-compression

encapsulation ppp

ip rtp compression-connections 25

For more information about RTP header compression, see the “Conﬁguring IP Multicast Routing”

chapter of the Network Protocols Conﬁguration Guide, Part 1.

Conﬁguring IP RTP Priority

IP RTP Priority provides a strict priority queueing scheme for delay-sensitive data such as voice.

Voice trafﬁccan be identiﬁed by its Real-TimeTransportProtocol (RTP) port numbers and classiﬁed

into a priority queue conﬁgured by the ip rtp priority command. The result is that voice is serviced

as strict priority in preference to other nonvoice trafﬁc.

This feature allows you to specify a range of User Datagram Protocol (UDP)/RTP ports whose voice

trafﬁc is guaranteed strict priority service over any other queues or classes using the same output

interface. Strict priority means that if packets exist in the priority queue, they are dequeued and sent

ﬁrst—that is, before packets in other queues are dequeued.

TheIP RTP Priorityfeaturedoes not require that you knowthe portofa voicecall. Rather,the feature

gives you the ability to identify arangeofportswhose trafﬁcisputintothe priority queue. Moreover,

you can specify the entire voiceport range—16384 to 32767—to ensure that all voice trafﬁcis given

strict priority service. IP RTP Priority is especially useful on slow-speed links whose speed is less

than 1.544 Mbps.

This feature can be used in conjunction with Weighted Fair Queueing (WFQ) on the same outgoing

interface.Trafﬁc matching the range of ports speciﬁed for the priority queue is guaranteed strict

priority over other WFQ ﬂows; voice packets in the priority queue are always serviced ﬁrst.

When used in conjunction with WFQ, the ip rtp priority command provides strict priority to voice,

and WFQ scheduling is applied to the remaining queues.

Because voice packets are small in size and the interface also can have large packets going out, the

Link Fragmentation and Interleaving (LFI) feature should also be conﬁgured on lower speed

interfaces. When you enable LFI, the large data packets are brokenup so that the small voicepackets

can be interleaved between the data fragments that make up a large data packet. LFI prevents a voice

packet from needing to wait until a large packet is sent. Instead, the voice packet can be sent in a

shorter amount of time.

For more information about the IP RTP Priority feature, see the IP RTP Priority Cisco IOS Release

12.0(5)T online document.

Command Purpose

router(config-if)# ip rtp compression connections

number

Specify the total number of RTP header compression

connections supported on an interface.

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 77 78

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