Table Of Contents
SA-Comp/1 and SA-Comp/4 Data Compression Service Adapters
SA-Comp/1 and SA-Comp/4 Data Compression Service Adapters
Description
The SA-Comp/1 and SA-Comp/4 data compression service adapters (CSAs) are available on Cisco 7200 series routers, on second-generation Versatile Interface Processors (VIP2s) in Cisco 7500 series routers, and on Cisco 7000 series routers with the 7000 Series Route Switch Processor (RSP7000) and 7000 Series Chassis Interface (RSP7000CI). (CSAs require VIP2 model VIP2-40.)
These service adapters provide high-performance, hardware-based data compression capabilities via simultaneous Stacker compression data compression algorithms with independent full-duplex compression and decompression capabilities on point-to-point (PPP) encapsulated packets.
The SA-Comp/1 supports up to 64 compression contexts and the SA-Comp/4 supports up to 256 compression contexts. There is one compression context per PPP link.
The CSA supports the compression and decompression of data passing through synchronous serial interfaces that are configured for a peak line rate of 16 Mbps or lower. You can use the CSA to compress and decompress data passing through any synchronous serial interface; however, the serial interface must be configured to send and receive data at a rate no greater than 16 Mbps. For example, the CSA supports high-speed serial interfaces (such as HSSI interfaces) if the interfaces are configured for a peak line rate of 16 Mbps or lower.
On the Cisco 7200 series routers you can optionally specify which CSA the interface uses to perform hardware compression.
Platforms
This feature is supported on these platforms:
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Cisco 7200 series
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Configuration Task
You can configure point-to-point compression on serial interfaces that use PPP encapsulation. Compression reduces the size of a PPP frame via lossless data compression. PPP encapsulations support both predictor and Stacker compression algorithms.
If the majority of your traffic is already compressed files, do not use compression.
When you configure Stacker compression on Cisco 7000 series routers with RSP7000, on Cisco 7200 series routers, and on Cisco 7500 series routers, there are three methods of compression: hardware compression, distributed compression, and software compression. Specifying the compress stac command with no options causes the router to use the fastest available compression method:
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Using hardware compression in the CSA frees the router's main processor for other tasks. You can also configure the router to use the VIP2 to perform compression by using the distributed option, or to use the router's main processor by using the software option. If the VIP2 is not available, compression is performed in the router's main processor.
When compression is performed in software installed in the router's main processor, it might significantly affect system performance. We recommend that you disable compression in the router's main processor if the router CPU load exceeds 40 percent. To display the CPU load, use the show process cpu EXEC command.
To configure compression over PPP, perform the following tasks in interface configuration mode:
Configuration Example
The following example enables hardware compression and PPP encapsulation on serial interface 3/1/0:
router(config)# interface serial 3/1/0router(config-if)# encapsulate ppprouter(config-if)# compress stacrouter(config-if)# exitrouter(config)#Command Reference
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.2 command references.
compress
To configure compression for Link Access Procedure, Balanced (LAPB), Point-to-Point Protocol (PPP), and High-Level Data Link Control (HDLC) encapsulations, use the compress interface configuration command. On Cisco 7000 series routers with RSP7000, Cisco 7200 series routers, and Cisco 7500 series routers, hardware compression on the compression service adapter (CSA) is supported for PPP links. To disable compression, use the no form of this command.
compress {predictor | stac}
no compress {predictor | stac}compress {predictor | stac [distributed | software]} (Cisco 7500 series and Cisco 7000 series
with RSP7000)
compress {predictor | stac [csa slot | software]} (Cisco 7200 series)Syntax Description
Default
Compression is disabled.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 10.0 (as compress predictor). The command compress {predictor | stac} first appeared in Cisco IOS Release 10.3.
This command was modified in Cisco IOS Release 11.2 P and 11.1 CA to include the distributed, software, and csa keywords.
Using CSA hardware compression on Cisco 7000 series routers with RSP7000, Cisco 7200 series routers, and Cisco 7500 series routers removes the compression and decompression responsibilities from the VIP2 or the main processor installed in the router. By using the compress stac command, the router determines the fastest compression method available on the router.
When using hardware compression on Cisco 7200 series routers with multiple CSAs, you can optionally specify which CSA is used by the interface to perform compression. If no CSA is specified, the router determines which CSA is used. On Cisco 7000 series routers with RSP700 and on Cisco 7500 series routers, the router uses the CSA on the same VIP2 as the interface.
You can configure point-to-point software compression for all LAPB, PPP, and HDLC encapsulations. Compression reduces the size of frames via lossless data compression. HDLC encapsulations supports the Stacker compression algorithm. PPP and LAPB encapsulations support both predictor and Stacker compression algorithms.
When compression is performed in software installed in the router's main processor, it might significantly affect system performance. We recommend that you disable compression if the CPU load exceeds 40 percent. To display the CPU load, use the show process cpu EXEC command.
Compression requires that both ends of the serial link be configured to use compression.
If the majority of your traffic is already compressed files, we recommend that you not use compression. If the files are already compressed, the additional processing time spent in attempting unsuccessfully to compress them again will slow system performance.
provides general guidelines for deciding which compression type to select.
Software compression makes heavy demands on the router's processor. The maximum compressed serial line rate depends on the type of Cisco router you are using and which compression algorithm you specify. shows a summary of the compressed serial line rates for software compression. The maximums shown in apply to the "combined" serial compressed load on the router. For example, a Cisco 4000 series router could handle four 64-kbps lines using Stacker or one 256-kbps line. These maximums also assume there is very little processor load on the router aside from compression. Lower these numbers when the router is required to do other processor-intensive tasks.
We recommend that you do not adjust the maximum transmission unit (MTU) for the serial interface and the LAPB maximum bits per frame (N1) parameter.
Note
Examples
The following example enables hardware compression and PPP encapsulation on serial interface 3/1/0:
interface serial 3/1/0encapsulate pppcompress stacThe following example enables predictor compression on serial interface 0 for a LAPB link:
interface serial 0encapsulation lapbcompress predictorRelated Commands
encapsulation lapb
encapsulation ppp
encapsulation x25
ppp compress
show compress
show processesshow compress
To display compression statistics, use the show compress EXEC command.
show compress
Syntax Description
This command has no arguments or keywords.
Command Mode
EXEC
Usage Guidelines
This command first appeared in Cisco IOS Release 10.0.
This information was modified in Cisco IOS Release 11.2 P and 11.1 CA to include sample output for hardware compression (implemented in the CSA hardware).
Sample Displays
The following is sample output from the show compress command when software compression is used on the router:
Router# show compressSerial0uncompressed bytes xmt/rcv 10710562/113768351 min avg ratio xmt/rcv 2.773/2.4745 min avg ratio xmt/rcv 4.084/3.79310 min avg ratio xmt/rcv 4.125/3.873no bufs xmt 0 no bufs rcv 0resets 0describes the fields shown in the display.
The following is sample output from the show compress command when hardware compression is enabled (that is, compression is implemented in the CSA hardware):
Router# show compressSerial6/1Hardware compression enabledCompressed bytes sent: 402 bytes 0 Kbits/sec ratio: 4.092Compressed bytes recv: 390 bytes 0 Kbits/sec ratio: 3.476restarts:1last clearing of counters: 1278 secondsdescribes the fields shown in the display. The information displayed by the show compress command is the same for hardware and distributed compression. For Cisco 7200 series routers with multiple CSAs, an additional line is displayed indicating the CSA in use.
Related Command
Supported MIB
The compression service adapters can be monitored with the Cisco Compression Service Adapter (CSA) MIB (CISCO-COMPRESSION-SERVICE-ADAPTER-MIB.my). For information on accessing Cisco MIB files, refer to the Cisco MIB User Quick Reference.
What to Do Next
For more information on the CSA service adapters, refer to the SA-Comp/1 and SA-Comp/4 Data Compression Service Adapter Installation and Configuration publication.
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