Figure 4.5 Average queue delay versus simulation time (transmission rate = 100 kbps)
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The latency between two nodes can be calculated as follows:
Latency = Transmit Time + Link Propagation + Queue Delay
Transmit Time = Size/Bandwidth
Link Propagation = Distance/Speed of Light
Since the transmit time and link propagation is fixed for a given topology and the total amount of data being sent, latency is mainly affected by the queuing delay. For the CRAFT network, the queuing delay includes the delay at the local buffer and the delay in routers during the transfer through internet.
The delay in routers for the internet is highly dynamic, thus it is very difficult to predict accurately the delay. On the other hand, the delay of data in the local buffer is strictly the transfer rate of data from PC onto the link. Therefore, the local delay can be predicted quite accurately. The following shows a plot of average queue delay for different durations of simulation time at a data transmission rate of 100 kbps:
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Figure 4.5 Average queue delay versus simulation time (transmission rate = 100 kbps) |
From the figure above, for example, it can be seen that for data rates of 100 kbps for 6 hours, the average queue delay is calculated to be 1.3 hours. At the time of this writing, the actual and simulated latency is still being investigated to see how well the numbers correlate with each other.