Cisco 2651XM Software Configuration Guide - Page 109
Configuring the Compression Network Module for the, Cisco 3600 Series Routers
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Chapter 3 Configuring with the Command-Line Interface Configuring the Compression Network Module for the Cisco 3600 Series Routers • The no fair-queue command disables fair queuing, which is enabled by default. This optimizes HSSI performance. • The no shutdown command enables the port. Configuring the Compression Network Module for the Cisco 3600 Series Routers Cisco 3640 and Cisco 3620 routers now support a compression port module that provides high-performance, hardware-based data compression using simultaneous Stacker compression algorithms. Independent full-duplex compression and decompression capabilities are used on point-to-point (PPP) encapsulated packets. A router's central processing unit is generally reserved for tasks such as creating and maintaining routing tables, not performing compression duties. When a hardware compression port module is used in a router, all compression activity is offloaded from the router's central processing unit. This kind of hardware configuration is needed for routers that require B-channel compression for multiple WAN connections, such as two ISDN PRI interfaces carrying 46 B channels. Signaling over the D channel is not compressed. One compression port module supports up to 128 WAN interfaces. WAN or serial connections have limited bandwidth and greatly benefit from compressed data. For example, a hardware compression card that achieves 2:1 compression can compress 500 bytes of data down to 250 bytes. Transmission time is reduced by 50 percent. A line that transmits at 56 kbps without compress transmits at 112 kbps with compression. An achieved compression ratio or rate is dependent on the type of file being compressed. Graphics files, sound files, and text files all have different compression requirements and results. A hardware card can compress and decompress outgoing and incoming data. For negotiated compression configured between two routers, the incoming compressed data sent by the remote router is decompressed by the receiving or local compression card. Configuration Task You can configure point-to-point compression on interfaces that use PPP encapsulation. Compression reduces the size of a PPP frame via lossless data compression. PPP encapsulations support Stacker and Predictor compression algorithms, but the compression port module installed in Cisco 3600 series routers support only Stacker compression over PPP encapsulations. If the majority of your traffic is already compressed files, do not use compression. A hardware compression card should be used if the router's main processor 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: Step 1 Step 2 Step 3 Command interface serial number encapsulation ppp compress stac Task Specify a serial interface. Enable encapsulation of a single protocol on the serial line. Enable compression on a specified WAN interface. OL-1957-04 Software Configuration Guide for Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series Routers 3-49