Quantum and Evolution Series Installation and Operating Handbook
8-51
The 40 bytes of IP, UDP and RTP headers are typically compressed to between 1 to 3
bytes. Currently the headers of TCP packets will
not
be compressed.
Ethernet header compression is also supported. The 14 bytes of Ethernet frame (the
Ethernet CRC is not sent over satellite even when compression is off) are typically
reduced to 1 byte.
Example: G.729 packet with 20ms (20 bytes) of payload:
• Original size = 40 byte header (IP+UDP+RTP) + 14 bytes Et 20 bytes
p 5 bytes HDLC
= 79 bytes
• Following compression = 1 byte header (IP+UDP+RTP) + 1 byte Et
20 bytes p 5 bytes HDLC
= 27 bytes (best case)
This represents more than a 60% bandwidth reduction.
There is support for ‘per route’ configuration control, where you can specify up to 32
source or destination IP addresses – only packets with one of these addresses get
directed through the compressor.
Header compression runs up to 29000 packets per second one-way, 22000 packets per
second two-way on the IP Traffic card.
8.12.13 VLAN
Operation
A VLAN allows virtual networks to be created as opposed to being limited to purely
physical segments. Benefits include creating a restricted broadcast domain so not
everyone sees all traffic, plus added security.
Three VLAN modes are supported:
•
Transparent VLAN operation in bridging mode
The modem supports IEEE 802.1q VLAN tags. If data is received with these tags
then the data, complete with tags, is transported transparently over satellite.
