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Table Of Contents
Express RTP Header Compression
Supported Standards, MIBs, and RFCs
Configuring Express RTP Header Compression
Express RTP Header Compression with PPP Encapsulation
Express RTP Header Compression with Frame Relay Encapsulation
ip rtp compression-connections
Express RTP Header Compression
Feature History
12.0(7)T
This feature was introduced.
12.1(4)E
This feature was integrated into Cisco IOS Release 12.1(4)E
12.2(14)S
This feature was integrated into Cisco IOS Release 12.2(14)S.
This document describes the Express RTP Header Compression feature in Cisco IOS Release 12.0(7)T, 12.1(4)E, and 12.2(14)S and includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
Before the introduction of the Express RTP Header Compression feature, if compression of Real-Time Transport Protocol (RTP) headers was enabled, compression was performed in the process-switching path. That meant that packets traversing interfaces that had RTP header compression enabled were queued and passed up to the process to be switched. This procedure slowed down transmission of the packet, and therefore some users preferred to fast switch uncompressed RTP packets.
Now, if RTP header compression is enabled, it occurs by default in the fast-switched path or the Cisco Express Forwarding-switched (CEF-switched) path, depending on which switching method is enabled on the interface. Furthermore, the number of RTP header compression connections has been increased to 1000 connections each.
If neither fast switching nor CEF switching is enabled, then if RTP header compression is enabled, it will occur in the process-switched path as before.
Benefits
The Express RTP Header Compression feature has the following benefits:
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Restrictions
When RTP header compression is configured on Multilink PPP interfaces that have link fragment and interleave (LFI), RTP packets originating on or destined to the router will be process switched. Transit traffic will be fast switched.
Related Documents
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Supported Platforms
This feature is supported on the following platforms in Cisco IOS Release 12.0(7)T and 12.1(4)E:
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This feature is supported on the following platforms in Cisco IOS Release 12.2(14)S:
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Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported on specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
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.
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
http://tools.cisco.com/ITDIT/MIBS/servlet/index
If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of supported MIBs and download MIBs from the Cisco MIBs page at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
To access Cisco MIB Locator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
RFCs
This feature supports the following RFCs:
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Prerequisites
In order for this feature to work, the following features must be in place:
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Configuration Tasks
Assuming that the prerequisites are met, RTP header compression is performed in the CEF-switched path or fast-switched path automatically. No configuration tasks are required. The following task is required:
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Configuring Express RTP Header Compression
By default, for Frame Relay encapsulation, there can be 256 RTP header compression connections (128 calls for each type). The maximum value is fixed, not configurable.
The software 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 which has HDLC or PPP encapsulation configured.
To change the number of compression connections supported, use the following command in interface configuration mode:
Step 1
Router(config-if)# ip rtp compression-connections number
Specifies the total number of RTP header compression connections supported on the interface.
Configuration Examples
This section contains the following express RTP header compression examples:
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Express RTP Header Compression with PPP Encapsulation
The following example shows a Cisco 7200 router configured with express RTP header compression and PPP encapsulation:
version 12.0no service padservice timestamps debug uptimeservice timestamps log uptimeno service password-encryption!hostname abc-1234!enable password lab!ip subnet-zerono ip domain-lookupip host xy-tftp 172.17.249.2clock timezone GMT 1clock summer-time GMT recurringip routingip cef!!controller E1 3/0!controller E1 3/1!!interface Ethernet2/0ip address 10.0.0.0 255.255.255.0no ip directed-broadcastno ip route-cache!interface Ethernet2/1ip address 10.0.0.1 255.255.255.0no ip directed-broadcastip route-cacheno shutdown!interface Serial4/0ip address 10.0.0.2 255.255.255.0no ip directed-broadcastencapsulation pppip rtp header-compression iphc-formatip rtp compression-connections 1000no ip mroute-cacheclockrate 2015232bandwidth 2000ip route-cacheno shutdown!interface Serial4/1no ip addressno ip directed-broadcastno ip route-cacheshutdownclockrate 2015232!ip default-gateway 10.0.0.3ip classlessip route 0.0.0.0 0.0.0.0 9.1.72.1!router igrp 1network 10.0.0.4!line con 0exec-timeout 0 0transport input noneline aux 0line vty 0 4password lablogin!no scheduler max-task-timeendExpress RTP Header Compression with Frame Relay Encapsulation
The following example shows a Cisco 7200 router configured with express RTP header compression and Frame Relay encapsulation:
version 12.0service timestamps debug uptimeservice timestamps log uptimeno service password-encryption!hostname ed1-72a!enable password lab!ip subnet-zerono ip domain-lookupip host xy-tftp 172.17.249.2clock timezone GMT 1clock summer-time GMT recurringip routingip cef!!controller E1 3/0!controller E1 3/1!interface Ethernet2/0ip address 10.0.0.0 255.255.255.0no ip directed-broadcastno ip route-cacheno ip mroute-cachentp broadcast client!interface Ethernet2/1ip address 10.0.0.1 255.255.255.0no ip directed-broadcastip route-cacheno ip mroute-cacheno shutdown!interface Serial4/0ip address 10.0.0.2 255.255.255.0encapsulation frame-relayframe-relay map ip 10.0.0.3 100 broadcast compressframe-relay ip rtp header-compressionno ip mroute-cacheip route-cachebandwidth 2000no keepaliveno shutdown!interface Serial4/1no ip addressno ip directed-broadcastno ip route-cacheno ip mroute-cacheshutdownno fair-queue!router igrp 1network 10.0.0.4!!ip default-gateway 10.0.0.5ip classless!map-class frame-relay fragframe-relay cir 64000frame-relay bc 1000frame-relay be 0frame-relay mincir 64000frame-relay adaptive-shaping becnframe-relay fair-queueframe-relay fragment 70!dialer-list 1 protocol ip permitdialer-list 1 protocol ipx permit!line con 0exec-timeout 0 0transport input noneline aux 0line vty 0 4password lablogin!!ntp clock-period 17179866endCommand Reference
This section documents the modified ip rtp compression-connections command. All other commands used with this feature are documented in the Cisco IOS 12.2 documentation set.
ip rtp compression-connections
To specify the total number of Real-Time Transport Protocol (RTP) header compression connections that can exist on an interface, use the ip rtp compression-connections command in interface configuration mode. To restore the default value, use the no form of this command.
ip rtp compression-connections number
no ip rtp compression-connections
Syntax Description
number
Number of RTP header compression connections the cache supports, in the range from 3 to 1000. The default is 32 connections (16 calls).
Defaults
32 connections
Command Modes
Interface configuration
Command History
Examples
The following example shows how to change the number of RTP header compression connections supported to 150:
interface serial 0encapsulation pppip rtp header-compressionip rtp compression-connections 150Related Commands