Q-Lite Satellite Modem Installation and Operating Handbook
6-51
routing populates the routing table based on information forwarded by
other routers in the network. The modem operates as a two-port router in
this mode (with separate terrestrial and satellite IP addresses).
Trunking
mode
Trunking mode implements a Layer 2 bridge in hardware. This results in a
much higher packet handling capability (up to 500,000 packets per
second as opposed to a maximum of 150,000 packets per second when
in other modes). Because the processor is bypassed in this mode, jitter is
also minimised and typically registers as zero when measured with
Ethernet test equipment. ACM (and AUPC) can be used in Trunking mode
but other IP features such as TCP acceleration cannot be used because
they require the packets to be passed through the processor.
Table 6-47 IP Mode
Control of Remote Modem in Bridge Mode
When the M&C and IP traffic ports are on the same subnet then the
ports can be bridged together (sharing a single address) and all
M&C requests will then automatically find their way to the remote
modem.
When the M&C and IP traffic ports are on separate subnets then
the following technique can be used. IP should be selected as the
mode for the ESC channel along with IP as the interface for the
main channel. If you then bridge the M&C to the traffic port, the
main channel runs as a separate bridge connected to the IP traffic
port but, at the same time, the ESC channel runs as a separate
bridge between the M&C ports of the two modems. The traffic for
each is completely separated. Separate subnets can be used for
M&C and IP traffic ports, since they retain individual addresses in
the specific case where both the ESC and main channel are both
set to IP mode.
If the M&C port were to be removed from the bridge then the IP
traffic port is still bridged over the main channel but the M&C
traffic will now pass no further than the local modem (unless
addressed to specific TCP ports, which can cause packets to be
forwarded over the ESC). This explicit control over what passes
through the ESC channel avoids bandwidth being potentially
wasted on broadcast M&C traffic.
The ESC channel is not available in DVB-S2 and DVB-S2X modes.
For this reason support for an M&C VLAN has been added that
causes all M&C traffic (on its own separate subnet) to pass over
satellite in its own VLAN, allowing easy M&C connectivity even
when using DVB-S2/S2X. Please see
Section 6.2.2.18
for further
details.