Test Results; Design Guidelines - HP 200 Series Services And Applications

Using these test files, HP routers were set up in various configurations and
file transfers were done across HP point-to-point links to determine accept-
able performance and throughput. Tests were conducted using both IP and
IPX protocols. The following section gives the results of this testing, and
compares them with results reported on other popular compression algo-
rithms. The test results lead to some guidelines for employing compression
on WAN links in routed networks. Those guidelines are detailed in the
"Design Guidelines" section following the test results.

Test Results

Using the Calgary Corpus files, observed compression ratios averaged 1.5:1.
Beware of vendors who claim very high compression ratios, as ratios are
entirely dependent on the content of the data being transferred. Basically,
any vendor can "customize" compressible text and claim ratios based on
those numbers. The reality is that with random LAN traffic, using packet-by-
packet compression techniques over non-reliable wide area links, 1.5:1 is a
reasonable number.

Design Guidelines

As a result of testing, the following guidelines should be observed when im-
plementing compression on HP Point-to-Point links.
1. HP Router 650 (card cage model holding up to 4 interface cards
or 16 ports):
Compression should not be run on WAN links with speeds
greater than 256 Kbit/s.
Since the HP PPC algorithm is implemented in software, it does
require CPU bandwidth to run. If compression is run on higher-
speed links, the throughput will likely not increase beyond that of a
256 Kbit/s link due to the required CPU bandwidth to compress and
decompress the data. This fact is true with any software-based
compression algorithm. The only way to achieve adequate
compression ratios on higher-speed links is to use a more expensive,
hardware-based compression algorithm. As a general rule of thumb,
the aggregate throughput numbers given below can help you
determine how many and what speeds of links will run successfully
on the Router 650.
Data Compression for WAN Links
Test Results
2-137