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QMultiFlex-400™ Installation and Operating Handbook
they are on the same subnet. A layer 2 bridge uses ethernet addresses to pass ethernet
frames, so IP addresses are not necessary. If multiple VLANs are being used (typical) then
it is absolutely necessary not to set an IP address (i.e. 0.0.0.0).
Teledyne Paradise Datacom has produced further application notes dealing with Star
topology and Mesh routing. Contact customer support for any documents listed in
14 Further
Reading.
8.7.2.1 Gateways
There is a single gateway address for the modem which can be used either for traffic or M&C
communications.
8.7.3
Throughput Performance
Actual throughput performance depends on a number of factors including one way/two-way
TCP or UDP 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 (This can be derated when
internal optimisation features are enabled). 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 up to 100Mbps with up to 4,400 concurrent accelerated TCP
connections and also supports at least 40,000 unaccelerated TCP connections.
8.7.4
Jumbo Ethernet Frame Support
The modem supports Ethernet frames up to 10k bytes in length.
8.7.5
IP Interoperability
The QMultiFlex-400™ interoperates with QFlex-400™, Q-Flex™ and Q-Lite™ remote
modems. In the case of a mesh system, all sites are required to have QMultiFlex-400™. All
QMultiFlex-400™ IP features have been adapted to work point-to-multipoint.
8.7.6
IP Connectivity Modes
The modem software supports unidirectional and bidirectional point-to-multipoint IP operation.
8.7.7
TCP Acceleration
TCP traffic, as opposed to UDP, requires acknowledgements to be returned to the sender
as part of the protocol flow control process. TCP was never intended for systems with long
delays (such as satellite). With no acceleration, TCP traffic over satellite would limit itself to
a few hundred kbit/s (depending on the PC TCP window size), regardless of the actual traffic
bandwidth available over satellite. Because the satellite delay is taken as evidence of link
congestion, TCP throttles back the amount of data it sends. Acceleration allows approx. 90%
utilisation of the available traffic bandwidth over satellite. Acceleration can be used in point-
to-multipoint bridging modes, as well as in routing mode.
8-37
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