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Using BlockSim for System
Capability Analysis
In highly available systems,
additional metrics of system capabilities are often needed for
system evaluation. In this article, we will explore an example
where
BlockSim's
throughput analysis capability is used in order to perform such
analysis.
Example of System Capability
via Throughput Analysis
Assume a signal is distributed
through a network to multiple antenna elements. The signal
originates at a single node. It is then distributed to 10
transmitters, each connected to 100 elements. This continues as
the signal is split out through various components until the
components directly connected to the 1,000 antenna elements are
reached. As node components fail, only a portion of the total
signal power delivered to the antenna elements is lost. However,
if the first node fails, all 1,000 elements are lost and there
is no signal. In order to quantify the capabilities of the
system in terms of its ability to deliver full signal strength,
reliability and availability metrics are not enough. Such a
highly redundant system is rarely unavailable. However, it often
operates at a lower capability. In order to be able to quantify
the signal strength, throughput analysis will be utilized.
Assume that a simplified
reliability block diagram (RBD) of the system is constructed as
shown below.
To represent this system in
BlockSim, a multiple block is utilized to represent 10
antenna elements in parallel. Each antenna element has a
throughput of 1 per unit time, while the nodes immediately
before and after the antenna elements have a throughput of 100,
as they "feed" 10 units to each of these 10 multiple blocks. The
starting and ending blocks in the main network have a throughput
of 1,000, as they feed 100 units to each of the 10 subsystems.
The properties of the antenna
elements are shown next (units are in hours).
The properties
of the nodes that feed the antenna elements are as follows:
When all components in the system are available, the
throughput is 1,000 units per hour. This is the equivalent
to full signal strength. If a node is down, it will make the
signal output of a set of 100 antenna elements unavailable.
Predictions for 1 year (8,760
hours) are of interest, with results broken down daily. The
simulation settings used are shown next.
A plot of the results
for the interval throughput is shown, where an interval is a
24-hour period.
Note that in a 24-hour period,
the system can process 24,000 units (24*1,000). Converting
the throughput to signal strength entails dividing the
interval throughput by 24,000. While the availability
remains at 100%, the signal strength goes down to 90% after
one year.
As can be seen, although the
availability of the system is high, the signal strength is
not at full capacity. Throughput analysis provides a better
understanding of the capability of the system in cases like
this.
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