COMNET III

Statistics
At the bottom of the monitor table are counter tables for message destination counters, link
counters, node counters, other transmission counters, buffer packet counters and other
counters.
1.2 Access Link Monitors
The simulation can monitor statistics for each access link’s entry and exit utilization, and
the statistics for the buffer size at the exit end. The buffer size is the number of framelevel
bytes (including frame overhead) that reside in the buffer for both the frames waiting
for transmission on the exit link and the frames currently transmitting on the exit link. The
link utilization is the ratio of the number of circuits busy transmitting frames divided by
the total number of circuits available. Generally there will be just a single circuit, and so
the basic utilization will have either the value of zero or one.
The event statistics are labeled as Exit Buffer Size, Entry Link Utilization, and Exit Link
Utilization. Observations of these events may be saved for plotting or post-run analysis.
However, there is an observation collected for each frame entering and leaving an access
link and, thus, there will generally be a very large number of observations to record.
Averaged statistics for the buffer size and link utilization are also available and they are
labeled as Mean Exit Buffer Size, Mean Entry Link Utilization, and Mean Exit Link Utilization.
These monitors will sample the averaged value at each sampling interval instead of each
event, and, thus, there will be fewer observations to plot. However, the averaging interval
can no longer be varied as part of the post-run analysis.
The average statistics may also be selected for real-time plots that will update at each update
interval during the simulation. These real-time monitors are labeled R-T Mean Exit Buffer
Size, R-T Mean Entry Utilization, and R-T Mean Exit Utilization, where R-T is an abbreviation
for real-time.
Note: The term “real-time” refers to the plots that are available and updating while the
simulation progresses. It does not refer to whether the simulation itself is running in real-time.
1.3 Virtual Circuit Monitors
For virtual circuits, the simulation can measure the frame delay and the leaky-bucket burst
size.
The frame delay is the time the frame takes to traverse the cloud from the moment it is created
at the input to the entry link to the time it is delivered at the output of the exit link. This frame
delay counts only the frames that successfully go through the cloud, and, thus, it does not
count frames that are dropped within the cloud. The frame delay monitor labeled Frame
Delay collects statistics for the delay for each frame that is delivered. The Mean Frame Delay
monitors the averaged frame delay over the mean-statistics interval, and the Real-Time Mean
Frame Delay provides a real-time plot of the averaged delay for this virtual circuit.
The Burst Size is the current size of the leaky-bucket burst at the time a frame is accepted
by the virtual circuit and, thus, the frame size is added to the burst. The Burst Size contains
only the data bytes for the encapsulated packets and, thus, it does not include the frame
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