Appendix H. Header And Payload Compression; Functional Overview - Comtec CDM-840 Installation And Operation Manual

H.1

Functional Overview

Header and Payload Compression are standard features provided in Comtech EF Data's
Advanced VSAT Series group of products, including the CDM-840 Remote Router.
The CDM-840 implements Payload Compression via the presence of a GZIP ASIC on the
CDM-840 main board. This integrated circuit provides the transmit compression and receive
decompression capabilities for maximum throughput and efficiency.
With Header Compression, the compression library that is incorporated into the CDM-840 for all
IP traffic can reduce 40-byte IP/UDP/RTP headers to as little as one (1) byte, or as little as three
(3) bytes for TCP/IP. For Voice-over-IP (VoIP), Header Compression provides bandwidth savings
greater than 64%.
For example, using an 8kbps G.729E voice codec requires 24 kbps of IP bandwidth once
encapsulated into an IP/UDP/RTP datagram. With Comtech EF Data's Header Compression
enabled, the same voice call requires only an approximate 8.5 kbps – a savings of almost 65%.
Additionally, bandwidth requirements for typical Web/HTTP traffic can be reduced by 10% or
more with TCP/IP Header Compression operation enabled.
With Payload Compression, the required satellite bandwidth can be reduced by as much as 40 to
50% based on Calgary Corpus files. The compression algorithm can be applied to all data, SLE,
and DVB-S2 header excluded. Compression statistics are fed back to the Quality of Service (QoS)
system in order to maximize WAN utilization while maintaining priority, latency, and jitter.
Appendix H. HEADER
PAYLOAD COMPRESSION
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