Configuring The Compression Network Module For The Cisco 3600 Series Routers; Configuration Task - Cisco 2620 Configuration Manual

Chapter 3 Configuring with the Command-Line Interface
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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
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The no fair-queue command disables fair queuing, which is enabled by default. This optimizes
HSSI performance.
The no shutdown command enables the port.
Command
interface serial number
encapsulation ppp
compress stac
Software Configuration Guide for Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series Routers

Configuring the Compression Network Module for the Cisco 3600 Series Routers

Task
Specify a serial interface.
Enable encapsulation of a single protocol
on the serial line.
Enable compression on a specified WAN
interface.
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