3.4 PPP Compression
3.4.1 Data compression
Cisco routers can also maximize performance by using data compression, which enables higher data throughput across the link.

Compression is a negotiated option. So, if the party you are calling is not configured for compression, no compression will take place.

The Cisco compression schemes are as follows:

  • Predictor-Determines whether the data is already compressed. If so, the data is just sent-no time is wasted trying to compress already compressed data.
  • Stacker-A Lempel-Ziv (LZ)-based compression algorithm looks at the data, and sends each data type only once with information about where the type occurs within the data stream. The receiving side uses this information to reassemble the data stream. (Stacker is the only supported algorithm in the Cisco 700 series.)
  • MPPC-This protocol (RFC 2118) allows Cisco routers to exchange compressed data with Microsoft clients. MPPC uses an LZ-based compression algorithm.
  • TCP header compression-This type of compression is used to compress the TCP headers.

The highest compression ratio is usually reached with highly compressible text files. Already compressed files such as JPEG graphics or MPEG files, or files that were compressed with software such as PKZIP or StuffIt, are only compressed 1:1, or even less.

If you frequently transfer already compressed data, such as graphics and video, you need to consider whether you want to globally set up compression. Trying to compress already compressed data can take longer than transferring the data without compression. Ideally, you can attain 2:1 or 3:1 compression for information that was not previously compressed. Expect an average of 1.6:1 compression for mixed compressed and uncompressed source data.

Compressing data can cause performance degradation because it is software, not hardware compression. Compression can be CPU or memory intensive.