Multiple Streams And Traffic Shaping - Teledyne QMultiFlex-400 Installation And Operating Handbook

QMultiFlex-400™ Installation and Operating Handbook

7.6 Multiple Streams and Traffic Shaping

Single stream mode allows a single MODCOD to be applied to the shared outbound carrier,
whereas with multiple streams, potentially different MODCODs can be applied to the
individual streams when they are transmitted over satellite in the shared outbound carrier (a
feature known as Variable Coding and Modulation (VCM)). VCM typically increases overall
throughput since it takes advantage of the fact that different remote sites will be at different
positions in the satellite footprint and will be capable of receiving different signal levels (hence
some will be able to use more bandwidth-efficient modulations and FEC rates than others).
There is no change to the overall symbol rate or power of the outbound carrier when VCM is
active - the configured bandwidth is simply shared between several different MODCODs in
accordance with the configured traffic shaping rules.
When the shared outbound is represented by a single stream (i.e. single MODCOD) then
the QoS classification methods are VLAN IDs, IP addresses, Diffserv and IEEE 802.1p
priority tags. When multiple streams are configured, the primary QoS method is VLAN ID
or IP address.
One thing to note with VCM is that the modem will not show the possible throughput for
each stream and this will typically need to be calculated from the set symbol rate and the
CIR rates set in the QoS.
For example:
Multiple Streams
Stream 1: 16APSK Rate ¾ Normal Frames (Pilots off)
Stream 2: 8PSK Rate ¾ Normal Frames (Pilots off)
Stream 3: QPSK Rate ½ Normal Frames (Pilots off)
Tx Symbol rate is set to 5Msym.
QoS
Stream 1: 33%CIR & 99%BIR Priority 1
Stream 2: 33%CIR & 99%BIR Priority 2
Stream 3: 33%CIR & 99%BIR Priority 3
So we can see the streams will all equally get 33% of the 5Msps symbol rate.
For each stream: 5Msps: 33% x 5Msps = 1.65Msps each.
To calculate the maximum throughput, it is necessary to use a rate calculator. Please
contact customer support for the bandwidth calculator (Excel spreadsheet).
Using the MODCOD for each stream and 1.65Msys as the symbol rate, the following bit
rates are calculated from the from the bandwidth calculator:
Stream 1: 4,895,101 bps
Stream 2: 3,676,404 bps
Stream 3: 1,631,616 bps
Traffic shaping configuration is covered in detail in the QoS description of this handbook
(see Sections 6.2.5
Adaptive Coding and Modulation (ACM) can optionally be used to maximize the efficiency of
the shared outbound. It does this by dynamically varying each VCM MODCOD (one per
& 8.7.8)
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