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Table Of Contents
Express RTP and TCP Header Compression
Supported Standards, MIBs, and RFCs
Changing the Number of Header Compression Connections
Express RTP Header Compression with PPP Encapsulation
Express RTP Header Compression with Frame Relay Encapsulation
ip rtp compression-connections
ip tcp compression-connections
Express RTP and TCP Header Compression
This feature module describes the Express RTP and TCP Header Compression feature. It includes information on the benefits of the new feature, supported platforms, related documents, and so forth.
This document includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
Before Cisco IOS Release 12.0(7)T, if compression of TCP or Real-Time Transport Protocol (RTP) headers was enabled, 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 process to be switched. This procedure slowed down transmission of the packet, and therefore some users preferred to fast switch uncompressed TCP and RTP packets.
Now, if TCP or 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 TCP and RTP header compression connections was increased to 1000 connections each.
If neither fast switching nor CEF switching is enabled, then if TCP or RTP header compression is enabled, it will occur in the process-switched path as before.
Benefits
The Express RTP and TCP Header Compression feature has the following benefits:
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Restrictions
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Related Documents
The TCP header compression aspect of this feature is related to these documents:
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The RTP header compression aspect of this feature is related to these documents:
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The CEF and fast switching aspects of this feature are related to these documents:
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Supported Platforms
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Prerequisites
In order for this feature to work, the following must be in place:
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Supported Standards, MIBs, and RFCs
Standards
None
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
This feature supports the following RFCs:
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Configuration Tasks
Assuming the prerequisites are met, TCP and RTP header compression is performed in the CEF-switched path or fast-switched path automatically. No 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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Express RTP Header Compression with PPP Encapsulation
The following example configures a Cisco 7200 router 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 9.1.72.104 255.255.255.0no ip directed-broadcastno ip route-cache!interface Ethernet2/1ip address 15.1.1.1 255.255.255.0no ip directed-broadcastip route-cacheno shutdown!interface Serial4/0ip address 15.3.0.1 255.255.255.0no ip directed-broadcastencapsulation pppip rtp header-compression iphc-formatip tcp 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 9.1.72.1ip classlessip route 0.0.0.0 0.0.0.0 9.1.72.1!router igrp 1network 15.0.0.0!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 configures a Cisco 7200 router 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 9.1.72.104 255.255.255.0no ip directed-broadcastno ip route-cacheno ip mroute-cachentp broadcast client!interface Ethernet2/1ip address 15.1.1.1 255.255.255.0no ip directed-broadcastip route-cacheno ip mroute-cacheno shutdown!interface Serial4/0ip address 15.3.0.1 255.255.255.0encapsulation frame-relayframe-relay map ip 15.3.0.2 100 broadcast compressframe-relay ip rtp header-compressionframe-relay ip tcp 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 15.0.0.0!!ip default-gateway 9.1.72.1ip 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 following revised commands. All other commands used in this document can be found in the Cisco IOS 12.0 documentation set.
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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 interface configuration command. To restore the default value, use the no form of this command.
ip rtp compression-connections number
no ip rtp compression-connectionsSyntax 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 changes the number of RTP header compression connections supported to 150:
interface serial 0encapsulation pppip rtp header-compressionip rtp compression-connections 150Related Commands
ip tcp compression-connections
To specify the total number of TCP header compression connections that can exist on an interface, use the ip tcp compression-connections interface configuration command. To restore the default, use the no form of this command.
ip tcp compression-connections number
no ip tcp compression-connections numberSyntax Description
number
Number of TCP 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
Usage Guidelines
You should configure one connection for each TCP connection through the specified interface.
Each connection sets up a compression cache entry, so you are in effect specifying the maximum number of cache entries and the size of the cache. Too few cache entries for the specified interface can lead to degraded performance, while too many cache entries can lead to wasted memory.
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Examples
The following example sets the first serial interface for header compression with a maximum of ten cache entries:
interface serial 0ip tcp header-compressionip tcp compression-connections 10Related Commands
