Table Of Contents
Distributed Compressed Real-Time Transport Protocol
Supported Standards, MIBs, and RFCs
Changing the Number of Header Compression Connections
Distributed Compressed RTP Header Compression
Express TCP Header Compression Example
show ip rtp header-compression
show ip tcp header-compression
Distributed Compressed Real-Time Transport Protocol
This feature module describes the distributed Compressed Real-Time Transport Protocol (dCRTP) feature.
This document includes the following sections:
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Supported Standards, MIBs, and RFCs
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Feature Overview
The dCRTP feature compresses the combined 40-byte IP/UDP/RTP packet headers to between two and four bytes on packets traveling on a Cisco 7500 series router with a Versatile Interface Processor (VIP) in distributed fast-switching and distributed Cisco Express Forwarding (dCEF) environments. This compression reduces the packet size, improves the speed of packet transmission, and reduces packet latency.
Before Cisco IOS Release 12.1(5)T, if compression of TCP or Real-Time Transport Protocol (RTP) headers was enabled on a Cisco 7500 series router with a VIP, the compression was performed in the process-switching path. That meant that packets traversing interfaces that had TCP or RTP header compression enabled were queued and passed up to the Route Switch Processor (RSP) to be switched. This procedure slowed down transmission of the packet, and therefore some users preferred to fast-switch uncompressed TCP and RTP packets rather than enable TCP and RTP compression.
If the dCRTP feature is enabled, the header compression of the combined IP/UDP/RTP header occurs by default in the distributed fast-switched path or the distributed Cisco Express Forwarding-switched (dCEF-switched) path, depending on which switching method is enabled on the interface.
If distributed fast-switching or distributed Cisco Express Forward switching are disabled, TCP or RTP header compression will occur in the process-switched path as before.
Benefits
Additional Functionality Capabilities for the RSP
The dCRTP feature offloads the IP/UDP/RTP header compression from the Route Switch Processor (RSP), scaling it for other functionality.
Enhanced 7500 Series Router Scalability for Enterprise and Service Provider Networks
The dCRTP feature helps support cRTP for large Enterprise and Service Provider networks on a single Cisco 7500 series router acting as an aggregation point.
Additional Support for Voice over IP Streams
The dCRTP feature allows for more Voice over IP (VoIP) streams to be supported without any major performance degradation on the RSP.
Accelerates Speed of Packet Transmission
The dCRTP feature reduces the size of the packet, which allows for a higher packet transmission speed.
Improved Latency
The dCRTP feature reduces the size of the packet. The smaller packet leaves less latency on a transmission ring, allowing for higher data quality.
Restrictions
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Related Documents
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Supported Platforms
This feature is supported on Cisco 7500 series routers with a Versatile Interface Processor
Supported Standards, MIBs, and RFCs
Standards
No new or modified Standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
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Prerequisites
In order for this feature to work, the following prerequisites must be met:
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Configuration Tasks
This document assumes that TCP or RTP header compression (or both) is already enabled. For information on configuring RTP header compression, see the Configuring Compressed Real-Time Protocol document on CCO and the Documentation CD-ROM. For information on configuring TCP header compression, see the "Compress TCP Packet Headers" section of the Configuring IP Services document on CCO and the Documentation CD-ROM.
If TCP or RTP header compression is enabled, the header compression is performed in the distributed CEF-switched or distributed fast-switched path automatically. No additional configuration tasks are required.
The following task is optional:
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Changing the Number of Header Compression Connections
By default, for Frame Relay encapsulation, there can be 256 TCP header compression connections and 256 RTP header compression connections (128 calls for each type). The maximum value is fixed, not configurable.
By default, for PPP or HDLC encapsulation, the software allows 32 TCP header compression connections (16 calls). This default can be increased to a maximum of 256 TCP header compression connections. The software also allows 32 RTP header compression connections (16 calls). This default can be increased to a maximum of 1000 RTP header compression connections on an interface.
To change the number of compression connections supported, use the appropriate command in interface configuration mode:
Configuration Examples
This section contains the following express RTP header compression examples:
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Distributed Compressed RTP Header Compression
The following example shows the output of the show ip rtp header command when a Cisco 7500 with a VIP has the dCRTP feature enabled. When the dCRTP feature is disabled, the distributed fast switched line of the output, which is in italics for emphasis, does not appear.
Router# show ip rtp headerRTP/UDP/IP header compression statistics:Interface Serial4/1/1:Distributed fast switched:8 seconds since line card sent last stats updateRcvd: 0 total, 0 compressed, 0 errors0 dropped, 0 buffer copies, 0 buffer failuresSent: 0 total, 0 compressed,0 bytes saved, 0 bytes sentConnect:16 rx slots, 16 tx slots,0 long searches, 0 misses 0 collisionsExpress TCP Header Compression Example
The following example shows the output of the show ip tcp header command when a Cisco 7500 with a VIP has the dCRTP feature enabled. When the dCRTP feature is disabled, the distributed fast switched line of output, which is in italics for emphasis, does not appear.
Router# show ip tcp headerTCP header compression statistics:Interface Serial4/1/1:Distributed fast switched: 8 seconds since line card sent last stats updateRcvd: 0 total, 0 compressed, 0 errors0 dropped, 0 buffer copies, 0 buffer failuresSent: 0 total, 0 compressed,0 bytes saved, 0 bytes sentConnect:16 rx slots, 16 tx slots,0 long searches, 0 misses 0 collisions
Command Reference
This section documents the following revised commands. All other commands used in this document can be found in the Cisco IOS 12.1 documentation set.
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show ip rtp header-compression
To show RTP header compression statistics, use the show ip rtp header-compression EXEC command.
show ip rtp header-compression [type number] [detail]
Syntax Description
type
(Optional) Specifies the interface type.
number
(Optional) Specifies the interface number.
detail
(Optional) Displays details of each connection.
Defaults
No default behavior or values.
Command Modes
EXEC
Command History
Usage Guidelines
The detail option is not available with the show ip rtp header-compression command on the RSP. However, the detail option is available with the show ip rtp header-compression commands on the VIP. Enter the show ip rtp header-compression interface detail command on the VIP to retrieve detailed information regarding RTP header compression on a specific interface.
Examples
The following example shows the output of the show ip rtp header-compression command when a Cisco 7500 with a VIP has the dCRTP feature enabled. When the dCRTP feature is disabled, the distributed fast switched line on output, which is italicized for emphasis, does not appear.
Router# show ip rtp header-compressionRTP/UDP/IP header compression statistics:Interface Serial4/1/1:Distributed fast switched:8 seconds since line card sent last stats updateRcvd: 0 total, 0 compressed, 0 errors0 dropped, 0 buffer copies, 0 buffer failuresSent: 0 total, 0 compressed,0 bytes saved, 0 bytes sentConnect:16 rx slots, 16 tx slots,0 long searches, 0 misses 0 collisionsRelated Commands
show ip tcp header-compression
To show TCP header compression statistics, use the show ip tcp header-compression EXEC command.
show ip tcp header-compression [type number] [detail]
Syntax Description
type
(Optional) Specifies the interface type.
number
(Optional) Specifies the interface number.
detail
(Optional) Displays details of each connection.
Defaults
No default behavior or values.
Command Modes
EXEC
Command History
Usage Guidelines
The detail option is not available with the show ip rtp header-compression and show ip tcp header-compression commands when distributed fast-switching is enabled. Users who need the detailed information for either of these commands can retrieve this information by disabling distributed fast-switching and then entering the show ip rtp header-compression detail or show ip tcp header-compression detail commands.
Examples
The following example shows the output of the show ip tcp header command when a Cisco 7500 with a VIP has the dCRTP feature enabled. When the dCRTP feature is disabled, the distributed fast switched line of output, which is italicized for emphasis, does not appear.
Router# show ip tcp header-compressionTCP header compression statistics:Interface Serial4/1/1:Distributed fast switched:8 seconds since line card sent last stats updateRcvd: 0 total, 0 compressed, 0 errors0 dropped, 0 buffer copies, 0 buffer failuresSent: 0 total, 0 compressed,0 bytes saved, 0 bytes sentConnect:16 rx slots, 16 tx slots,0 long searches, 0 misses 0 collisionsRelated Commands
Guest