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.