Comtech EF Data turboIP v4.0 - Manual (Page 17)

turboIPv4.0 Revision 6
Overview MN/TURBOIP.IOM
1.5 D ATA AND H EADER C OMPRESSION
The turboIP supports header and payload compression of accelerated TCP traffic. Compression is
enabled or disabled by a global setting. If it is enabled, both header and data compression will be
attempted on all new accelerated sessions. Compression will be negotiated during the TCP
connection establishment. Therefore, even if the turboIP has compression enabled, and if the peer
turboIP does not also have compression enabled, then the session will not be compressed.
Data compression on accelerated TCP flows will be handled on a segment-by-segment basis. The
compressibility of each segment payload will be evaluated individually and only those segments
where the impacts would be beneficial will be compressed.
If a session is to be compressed, then the segments corresponding to that session will be
compressed only if:
1. the uncompressed payload length is greater than 90 octets;
and,
2. the compressed length is not larger than two octets smaller than the uncompressed
length.
1.5.1 M
INIMUM
C
OMPRESSION
R
ATIO
The compression ratio is defined as the ratio of the sum of the sizes of all TCP segments in an
uncompressed session to the sum of the sizes of the TCP segments if that same session were
compressed. Note that this is different from the definition used in the compression ratio statistic.
A minimum compression ratio of 1.91:1 shall be achieved with the Canterbury corpus and 1.63:1
with the Calgary corpus, when the data is transferred through the turboIP using FTP.
The turboIP shall never produce a compression ratio less than 1 with any data, that is, the size of
the compressed flows shall always be less than or equal to the size that the flow would have been
if compression were disabled for that flow.
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