Comtech EF Data CDM-570A - Manual (Page 475)

CDM-570L/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix D Revision 2
D–17
• Header Compression Statistics will display the total bytes of the pre-compressed and post-
compressed traffic and effective compression ratio.
D.1.2.7.2.2 Payload Compression
The Packet Processor features industry-leading payload compression for IP traffic. Implemented
in the hardware for maximum throughput and efficiency, payload compression can reduce the
required satellite bandwidth by as much as 40–50%. Traffic optimization through Payload
Compression is an optional feature of the Packet Processor. Note the following:
• Available as a FAST feature
• Uses AHA chip
• Compression algorithm applied to all data (HDLC header excluded)
• Compression statistics are fed back to QoS in order to maximize WAN utilization while
maintaining priority, jitter and latency
• 1024 simultaneous compression sessions to maximize compression across multiple distinct
traffic flows
• Compression algorithm not applied to RTP streams because this traffic is already
compressed and would only INCREASE the sat bandwidth if compressed again
• Additional statistics have been added to the compression statistics menu in order to provide
feedback on the compression efficiency that has been achieved
• Payload Compression is selectable on a per route basis
D.1.2.7.2.3 ALDC vs. LZS Compression Comparison
Algorithm Payload
size
File Set Ratio Algorithm
Payload
size
File Set Ratio
ALDC
1472
Calgary
1.76
LZS
1472
Calgary
1.66
1000 1.76 1000 1.66
500 1.77 500 1.68
100 2.09 100 1.97
1472
Canterbury
1.71 1472
Canterbury
1.61
1000 1.72 1000 1.62
500 1.74 500 1.63
100 2.04 100 1.91
The numbers in this table were compiled using a test program created in-house by Comtech EF
Data. This program takes the target benchmark files and splits the files into payload-sized
chunks, then compresses each chunk in a separate invocation of the compression algorithm.
This is important to note because most compression algorithms are applied to the entire file
data set as a single invocation of the compression algorithm, which is easier for other types of