The message compression compresses WinCC OA messages. Data compression
means encoding information using fewer bits than an unencoded
representation would use through use of specific encoding schemes.
Compression is useful because it reduces the consumption
of expensive resources, such as transmission bandwidth.
Use the config entry ”messageCompression”
to specify the compression scheme. The config entry may contain
the following schemes:
"none"
(no compression), (default value is "" meaning "none") "zlib"
(compression using zlib (gzip, zip)), see http://www.zlib.org
"bzip2"
(compression by using the bzip2 algorithm (bzip2 is
a freely available, high-quality data compressor, see http://www.bzip.org).
"bzip2 compresses better than zlib at the cost of higher
CPU utilization.
or "zlib-bzip2" (compresses
short messages using zlib and bigger messages like Identification
using bzip2)
You can use the config entry in all config file
sections.
You can specify several schemes, for example, messageCompression = "zlib-bzip2,zlib".
The client and the server agree on the first common scheme. Therefore,
if you configure "zlib" on
the client and "bzip,zlib"
on the server, the "zlib"
scheme is used. The default value is
"none" and we recommend to use "zlib-bzip2".
The message compression compresses WinCC OA messages only as
of a specific minimum size to avoid unnecessary CPU load. Specify
the size in bytes using the config entry ”messageCompressionThreshold”
(Default 0). You can use the config entry in all config file sections.
The message compression provides a considerable advantage by reducing
the consumption of transmission bandwidth noticeable, even in
case of small messages. The default value 0 compresses all messages
as long as the compression provides an advantage (sometimes compressed
data might be bigger than uncompressed). The compression only
compresses messages of external connections. It does not compress
messages of local (computer) connections.
Use the -report dispatch
option to query the compression rate. 20 % means that the message
compression compressed a message to 1/5 of the original size.
The rate results from the size of the transmitted reference data
divided by the size of the not compressed data. |
