ND SatCom SKYWAN IDU 7000, Manual

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50 Network Design and Engineering Guide 2010-10-26
General Carrier Design
Network Traffic Estimation
timate data requirements in transmit direction separately. This argument holds as long as the
transmission of data is evenly distributed among the stations, which is typically the case for a
meshed network. It may not be valid however, if the transmission is concentrated on few or only
one station, like in the case of a single hub star network.
Let us consider the following example : A single hub star network consisting of the hub station
and 10 remote terminals. For the sake of simplicity we assume that only non real-time traffic
should be supported with a committed data rate (in receive direction) of 500 kbps for the hub
station and 100 kbps for each remote terminal. Putting the hub station on carrier 1 and the ter-
minals on carrier 2 we have the following data rate requirements for the carriers:
Carrier 1: 500 kbps
Carrier 2: 1000 kbps
Let’s now assume that the network should be extended by another 10 remote terminals. As-
suming the same data rate requirements for the additional terminals, the new summary require-
ment for the second carrier would be:
Carrier 2: 2000 kbps
If the hub station could not support the additional bandwidth due to power limitations, one might
be tempted to increase the network capacity by adding an additional carrier instead, i.e. having
a carrier configuration like:
Carrier 2: 1000 kbps
Carrier 3: 1000 kbps
If the additional 10 stations are assigned to the new carrier 3, such a solution would formally
fulfill the capacity requirements of the enlarged network according to the carrier configuration
worksheet of the capacity calculation tool. This could only lead to problems if all stations have
to be served with a datarate of 100 kbps at the same time. In reality however the throughput
from the hub to all remote terminal stations would still be limited to 1000 kbps only. The reason
is that the hub station cannot simultaneously transmit on both carrier 2 and 3. To increase the
throughput from hub to remote terminals there are only two possible solutions:
-
Increase the maximum power level on the hub station to allow larger bandwidths.
- Migrate to a double-hub star network: In this case one hub station may transmit on carrier
2 when simultaneously the second hub transmits on carrier 3. This allows the full utilization
of the available bandwidth of both carriers. Additional benefit would be an improved redun-
dancy in the network: If one hub fails traffic to the remotes could still be forwarded via the
second hub.