Product specifications

CDD-562L/564 Demodulator with IP Module Revision 1
IP Module Ethernet Interface Overview MN/CDD564L.IOM
6–4
Header Compression reduces the required VoIP bandwidth by 60 percent. Example: A G.729a
voice codec, operating at 8 kbps, will occupy 32 kbps once encapsulated into IP framing on a
LAN. Using IP/UDP/RTP Header Compression, the same traffic only needs 10.8 kbps total WAN
satellite bandwidth to cross the link. A total maximum of 64 simultaneous VoIP calls can be
compressed. Normal Web/HTTP traffic can be reduced an additional 10% via IP/TCP header
compression.
Header Compression Configuration – Header Compression is completely independent from
QoS, and there is no configuration required except enabling the Header Compression feature on
both the sending and receiving Comtech EF Data IP modem/demod. Packets with a Header
Compression supported header will automatically be identified for compression. The only
configuration consideration is the Header Compression Refresh Rate. This is how many
compressed header packets will be sent before a single full header packet is sent. Sometimes
compressed header traffic could be lost during deteriorated satellite link conditions. Sending a full
header packet will allow the return of the traffic stream. The Refresh Rate can be increased for
poor satellite link conditions or decreased to further reduce overhead.
6.3.3 Payload Compression
Traffic optimization through Payload Compression is another optional feature of the demodulator.
• FAST feature to upgrade
• 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 satellite 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.
6.3.3.1 ADLC vs LZS Compression Comparison
These numbers have been generated using an internally created test program. This program
takes the target benchmark files and splits the files into payload size chunks and 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 compression
algorithms (LZS, GZIP in specific). This, of course, does not apply to streamed packet data
across an IP network (e.g., FTP transfer).