Specifications

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Cisco 1751 Router Software Configuration Guide
OL-1070-01
Enable RTP Header Compression on a Serial Interface
You need to enable compression on both ends of a serial connection. To enable RTP header
compression, use the following interface configuration command:
Router(config-if)# ip rtp header-compression [passive]
If you include the passive keyword, the software compresses outgoing RTP packets only if incoming
RTP packets on the same interface are compressed. If you use the command without the passive
keyword, the software compresses all RTP traffic.
Change the Number of Header Compression Connections
By default, the software supports a total of 16 RTP header compression connections on an interface. To
specify a different number of RTP header compression connections, use the following interface
configuration command:
Router(config-if)# ip rtp compression connections number
RTP Header Compression Configuration Example
The following example enables RTP header compression for a serial interface:
Router(config)# interface serial0
Router(config-if)# ip rtp header-compression
Router(config-if)# encapsulation ppp
Router(config-if)# 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 for Cisco IOS Release 12.1T.
Configure Custom Queuing
Some QoS features, such as IP RTP reserve and custom queuing, are based on the transport protocol
and the associated port number. Real-time voice traffic is carried on UDP ports ranging from 16384 to
16624. This number is derived from the following formula:
16384 + (4 x number of voice ports in the router)
Custom Queuing and other methods for identifying high priority streams should be configured for these
port ranges. For more information about custom queuing, refer to the “Managing System Performance”
chapter in the Configuration Fundamentals Configuration Guide for Cisco IOS Release 12.1T.
Configure Weighted Fair Queuing
Weighted fair queuing ensures that queues do not starve for bandwidth and that traffic gets predictable
service. Low-volume traffic streams receive preferential service; high-volume traffic streams share the
remaining capacity, obtaining equal or proportional bandwidth.
In general, weighted fair queuing is used in conjunction with multilink PPP with interleaving and RSVP
or IP precedence to ensure voice packet delivery. Use weighted fair queuing with multilink PPP to
define how data is managed; use RSVP or IP precedence to give priority to voice packets. For more
information about weighted fair queuing, refer to the “Managing System Performance” chapter in the
Configuration Fundamentals Configuration Guide for Cisco IOS Release 12.1T.