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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:
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.
The Express RTP and TCP Header Compression feature has the following benefits:
One restriction affects Multilink PPP interfaces that have link fragment and interleave (LFI). In this case, if RTP header compression is configured, RTP packets originating on or destined to the router will be process switched. Transit traffic will be fast switched.
The TCP header compression aspect of this feature is related to these documents:
The RTP header compression aspect of this feature is related to these documents:
The CEF and fast switching aspects of this feature are related to these documents:
In order for this feature to work, the following must be in place:
None
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.
This feature supports the following RFCs:
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:
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:
| Command | Purpose |
|---|---|
Specifies the total number of TCP header compression connections supported on the interface. | |
Specifies the total number of RTP header compression connections supported on the interface. |
This section contains the following express RTP header compression examples:
The following example configures a Cisco 7200 router with express RTP header compression and PPP encapsulation:
version 12.0 no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname abc-1234 ! enable password lab ! ip subnet-zero no ip domain-lookup ip host xy-tftp 172.17.249.2 clock timezone GMT 1 clock summer-time GMT recurring ip routing ip cef ! ! controller E1 3/0 ! controller E1 3/1 ! ! interface Ethernet2/0 ip address 9.1.72.104 255.255.255.0 no ip directed-broadcast no ip route-cache ! interface Ethernet2/1 ip address 15.1.1.1 255.255.255.0 no ip directed-broadcast ip route-cache no shutdown ! interface Serial4/0 ip address 15.3.0.1 255.255.255.0 no ip directed-broadcast encapsulation ppp ip rtp header-compression iphc-format ip tcp header-compression iphc-format ip rtp compression-connections 1000 no ip mroute-cache clockrate 2015232 bandwidth 2000 ip route-cache no shutdown ! interface Serial4/1 no ip address no ip directed-broadcast no ip route-cache shutdown clockrate 2015232 ! ip default-gateway 9.1.72.1 ip classless ip route 0.0.0.0 0.0.0.0 9.1.72.1 ! router igrp 1 network 15.0.0.0 ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password lab login ! no scheduler max-task-time end
The following example configures a Cisco 7200 router with express RTP header compression and Frame Relay encapsulation:
version 12.0 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname ed1-72a ! enable password lab ! ip subnet-zero no ip domain-lookup ip host xy-tftp 172.17.249.2 clock timezone GMT 1 clock summer-time GMT recurring ip routing ip cef ! ! controller E1 3/0 ! controller E1 3/1 ! interface Ethernet2/0 ip address 9.1.72.104 255.255.255.0 no ip directed-broadcast no ip route-cache no ip mroute-cache ntp broadcast client ! interface Ethernet2/1 ip address 15.1.1.1 255.255.255.0 no ip directed-broadcast ip route-cache no ip mroute-cache no shutdown ! interface Serial4/0 ip address 15.3.0.1 255.255.255.0 encapsulation frame-relay frame-relay map ip 15.3.0.2 100 broadcast compress frame-relay ip rtp header-compression frame-relay ip tcp header-compression no ip mroute-cache ip route-cache bandwidth 2000 no keepalive no shutdown ! interface Serial4/1 no ip address no ip directed-broadcast no ip route-cache no ip mroute-cache shutdown no fair-queue ! router igrp 1 network 15.0.0.0 ! ! ip default-gateway 9.1.72.1 ip classless ! map-class frame-relay frag frame-relay cir 64000 frame-relay bc 1000 frame-relay be 0 frame-relay mincir 64000 frame-relay adaptive-shaping becn frame-relay fair-queue frame-relay fragment 70 ! dialer-list 1 protocol ip permit dialer-list 1 protocol ipx permit ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password lab login ! ! ntp clock-period 17179866 end
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.
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
number | Number of RTP header compression connections the cache supports, in the range from 3 to 1000. The default is 32 connections (16 calls). |
32 connections
Interface configuration
| Release | Modification |
|---|---|
11.3 | This command was introduced. |
12.0(7)T |
|
The following example changes the number of RTP header compression connections supported to 150:
interface serial 0 encapsulation ppp ip rtp header-compression ip rtp compression-connections 150
| Command | Description |
|---|---|
frame-relay ip rtp header-compression | Enables RTP header compression for all Frame Relay maps on a physical interface. |
frame-relay map ip rtp header-compression | Enables RTP header compression per DLCI. |
ip rtp header-compression | Enables RTP header compression. |
ip tcp header-compression | Enables TCP header compression. |
show ip rtp header-compression | Displays RTP header compression statistics. |
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
number | Number of TCP header compression connections the cache supports, in the range from 3 to 1000. The default is 32 connections (16 calls). |
32 connections
Interface configuration
| Release | Modification |
|---|---|
10.0 | This command was introduced. |
12.0(7)T | For Frame Relay, PPP, and High-Level Data Link Control (HDLC) encapsulation, the maximum number of compression connections increased to 256. For Frame Relay, the maximum value is fixed, not configurable. |
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.
The following example sets the first serial interface for header compression with a maximum of ten cache entries:
interface serial 0 ip tcp header-compression ip tcp compression-connections 10
| Command | Description |
|---|---|
ip rtp header-compression | Enables RTP header compression. |
ip tcp header-compression | Enables TCP header compression. |
show ip rtp header-compression | Displays RTP header compression statistics. |
Posted: Fri Dec 10 18:44:30 PST 1999
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