Q-Flex Satellite Modem Installation and Operating Handbook
7-20
7.8.2 IP Addressing
The two ports on the IP card are bridged together, acting as a two-port switch. This is true
regardless of what bridging or routing mode is selected. In bridging mode, IP addresses are
not used so there is no restriction on what subnets are off the two traffic card ports. In
routing mode, since the IP traffic card has a single address covering both ports, there can
only ever be one direct subnet off the two ports.
•
With an IP card fitted and the base modem M&C port out of the bridge then the base
modem IP traffic port is not addressable.
•
With an IP card fitted and the two base modem ports bridged then base modem
access can be used for M&C only – no base modem data will be passed over satellite.
•
If no IP traffic card is fitted and the M&C port is out of the bridge (i.e. the traffic port has
its own IP address) then the IP traffic port and M&C port
must
be on different subnets
because otherwise the modem does not know which of the two ports to respond out of.
7.8.2.1 Gateways
There is a single gateway address for the modem.
7.8.3 Throughput Performance
Actual throughput performance depends on a number of factors including one way/two way
traffic, packet size, data rates and the mixture of IP features switched on. There are
endless combinations and therefore it is strongly recommended that empirical testing is
undertaken prior to deployment to ensure that the required level of service can be provided.
The modem can process up to 150,000 packets per second. (In Trunking mode this
increases to 500,000 packets to second.) It is good practice to put a switch (or router)
between the modem and local network in order to minimize the number of packets the
modem has to process, as incidental network traffic (not intended for satellite) has the
potential to push the modem over it packet processing limit.
TCP acceleration works to the maximum data rate of the modem.
Header compression on the IP Traffic card works to 58,000 packets per second one way,
29,000 two way.
7.8.4 Jumbo Ethernet Frame Support
The modem supports Ethernet frames up to 10k bytes in length. For optical Ethernet, this is
increased to 16k bytes.
7.8.5 IP Over ESC
The Engineering Service Channel (ESC) is a low rate independent data channel from the
main data channel that exists within some framed satellite services such as IBS and
Closed Network plus ESC. It was originally intended for inter-earth station communications
and is often used for M&C control of remote equipment.
