Specifications

Configure a Synchronous Serial Interface

IC-74

Cisco IOS Interface Configuration Guide

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.

Note If the majority of your trafﬁc is already compressed ﬁles, do not use compression.

When you conﬁgure Stacker compression 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, as described here:

• If the router contains a compression service adapter (CSA), compression is performed in the CSA

hardware (hardware compression).

• If the CSA is not available, compression is performed in the software installed on the VIP2

(distributed compression).

• If the VIP2 is not available, compression is performed in the router’s main processor (software

compression).

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. You should 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.

For instructions on conﬁguring compression over PPP, refer to the “Conﬁguring Media-Independent

PPP and Multilink PPP” chapter in the Dial Solutions Conﬁguration Guide.

Conﬁgure Compression of HDLC Data

You can conﬁgure point-to-point software compression on serial interfaces that use HDLC

encapsulation. Compression reduces the size of a HDLC frame via lossless data compression. The

compression algorithm used is a Stacker (LZS) algorithm.

Compression is performed in software and might signiﬁcantly affect system performance. We

recommend that you disable compression if CPU load exceeds 65 percent. To display the CPU load,

use the show process cpu EXEC command.

If the majority of your trafﬁc is already compressed ﬁles, you should not use compression.

To conﬁgure compression over HDLC, use the following commands in interface conﬁguration

mode:

Step Command Purpose

1 encapsulation hdlc Enable encapsulation of a single protocol on the serial

line.

2 compress stac Enable compression.