SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 72 (160)
14. Header Compression
The header compression feature has been implemented into the STM SatLink system to reduce the
required bandwidth, especially for VoIP calls. But also other application benefits by 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 STM 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 if 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 transmit traffic as usual, without header
compression.
To check if the Header Compression is an available feature on the SatLink Hub, connect to the CLI
interface of the VSAT, and 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
Default CW Frequency : 0.000000 GHz
ATM mode : VC-Mux
Header Compression : RTP/UDP/IP/DSM-CC
Satellite (DVB) Transmitter Status
--------------------------------
State : On (TDMA)
Timeout : 0 min 0 sec
IDU Output Power : -15.2 dBm
Eb/No : 21.0 dB
Header Compression : RTP/UDP/IP/DSM-CC
Timing correction : 152 us (10623 us)
Frequency correction : -70 Hz
The text in bold shows the configured values and the status. 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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