14. Header Compression
The header compression feature has been implemented into the SatLink system to reduce the required
bandwidth, especially for VoIP calls. But there are also other application benefits with the Header
Compression feature. Header compression greatly reduces the amount of overhead associated with each
encapsulated IP packet. It is accomplished by removing (or reducing) redundant information in the packet
headers at one or more layers.
There are two options when using header compression on the SatLink system. One is to enable header
compression only for the DSM-CC header. The other option is to enable it for both DSM-CC and
RT/IP/UDP header.
14.1 Enabling Header Compression
The VSAT will detect whether the GW has the Header Compression enabled and only use the feature if it
is available on the SatLink Hub. If the Header compression is enabled on the VSAT but not on the
SatLink Hub, it does not take effect. The VSAT will then continue to transmit traffic as usual without
header compression.
To check if header compression is an available feature on the SatLink Hub, connect to the CLI interface
of the VSAT, enable DSM-CC and UDP Header Compression, and check the transmit status as shown in
the example below.
# dvb hdrcomp +dsmcc
# dvb hdrcomp +udp
# dvb tx show
Satellite (DVB) TX Configuration
Auto start : Enabled
IDU output power : -15 dBm
IDU max output power : 0.0 dBm
EIRP : 46.0 dBW
Default CW Frequency : 0.000000 GHz
ATM mode : VC-Mux
Header Compression : RTP/UDP/IP/DSM-CC
Satellite (DVB) Transmitter Status
State : On (TDMA)
IDU Output Power : -15.2 dBm
ODU Output Power : 32.7 dBm
EIRP : 42.4 dBW
Es/No : 21.0 dB
Header Compression : UDP/IP/DSM-CC
Timing correction : 152 us (10623 us)
Frequency correction : -70 Hz
In this example, header compression is enabled on both the VSAT and the SatLink Hub. Always
remember to save the new configuration with the command save config.
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