Comtech EF Data CDM-IP 300L - Manual (Page 42)

CDM-IP 300L IP-Centric Satellite Modem Rev. 1
CD/CDMIP300L.IOM
14
1.4.3 IP H
EADER
C
OMPRESSION
Header Compression is also an optional feature of the CDM-IP modem. The CDM-IP
supports Header Compression for the following Ethernet and Layer 3 & 4 Headers:
Supported Ethernet Headers
Ethernet 2.0
Ethernet 2.0 + VLAN-tag
Ethernet 2.0 + MPLS
802.3-raw
802.3-raw + VLAN-tag
802.3 + 802.2
802.3 + 802.2 + VLAN-tag
802.3 + 802.2 + SNAP
802.3 + 802.2 + SNAP + VLAN-tag
802.3 + 802.2 + SNAP + MPLS
Supported Layer 3&4 Headers
IP
TCP
UDP
RTP (Codec Independent)
Header Compression reduces the required VoIP bandwidth by 60%. 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 CDM-IP modem. 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. Some 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.
Header Compression Statistics - These statistics will display the total bytes of the pre-
compressed and post-compressed traffic and effective compression ratio.