Q-Lite Satellite Modem Installation and Operating Handbook
7-43
7.13 Point-to-multipoint Interoperation with Q-MultiFlex
The Q-Flex can receive a shared outbound from a Q-MultiFlex unit and generate an
inbound carrier that is received by one of the sixteen demodulators in the Q-MultiFlex.
This section explains the different modes that can be used. Bridging, VLAN tagging and
routing are all supported. Remote M&C traffic can be passed in its own special VLAN
(which creates convenient separation from user traffic) regardless of whether VLANs are
or aren’t being used more generally. Traffic and M&C ports can be on separate subnets if
required.
When using DVB-S2/S2X, the shared outbound carrier from the Q-MultiFlex can be
composed of a single modcod (i.e. modulation and FEC rate) or of a unique modcod for
each remote modem (up to 16 modcods are supported). (This form of multistreaming is
sometimes referred to as VCM.) There is no limit to the number of remote modems that
can share a single outbound since multiple Q-MultiFlex units can be cascaded together to
share the same outbound. The Q-Flex is capable of filtering on a single stream (modcod)
in the shared outbound. The modcod will be chosen depending on the signal strength
received at the remote modem. For example, one site may be able to receive only QPSK
9/10 while another may be able to receive 8PSK ¾ and another 16APSK 8/9. The
spectral efficiencies of each of these vary considerably and therefore throughput can be
maximised for each remote site at the same time.
In addition, point-to-multipoint DVB-S2/S2X ACM is supported. In this scenario, each
remote modem reports back its current Es/No and the Q-MultiFlex will change each of the
modcods independently in the shared outbound in order to maximise the throughput for
the current conditions being experienced at each remote.
In all cases when interoperating with a Q-MultiFlex, the Q-Flex must have the point-to-
multipoint setting set to
Point-to-multipoint
or
Point-to-multipoint-multistreaming
as
described in Section
6.3.2.8
, which also describes how the Q-Flex can filter on a single
stream (modcod) from the shared outbound. VLAN tags can be attached/removed
internally by the Q-MultiFlex and Q-Flex or can be handled outside of the modems (by
Ethernet switches for example). A VLAN can optionally be associated with each modcod
in the shared outbound. Filtering at the Q-Flex in this case is by
Stream Identifier
and by
the VLAN ID. VLAN filtering can also be used in the case where the shared outbound
consists of only a single modcod. In all cases, traffic shaping can be used to allocate
bandwidth to VLANs and/or modcod streams.
When point-to-multipoint ACM is being used on the Q-Flex, the setup is the same as for
Point-to-multipoint-multistreaming
mentioned above with the addition that the ACM
feature is switched on in the Q-Flex (specifically being set to
Monitor
mode). It is
important that the ‘nominal’ modcod set for the Q-Flex represents the highest modcod
that ACM should use when selecting a modcod for the remote modem as part of the
shared outbound carrier. For example, the RF constraints of one remote site may mean
that the highest modcod that can be used is 8PSK ¾ whereas another site may be able to
use 16APSK 9/10. In all cases, the symbol rate for the received carrier should be set to
the overall symbol rate of the shared outbound, which does not vary regardless of the set
of modcods being generated by the Q-MultiFlex.
