These notes were typed in live during the lecture
Q2 CE321 2019
A network operator provides 25 data circuits, each with a capacity of
100 Mb/s as an on-demand service to customers at a business
park. These data circuits are designed to provide extra capacity on a
first-come-first-served basis to customers that need them; they are in
addition to permanent network connections that the customers
use. Customers are billed per-hour of usage for these on-demand
circuits as an incentive to only use them as needed. Only one customer
at a time can use a single data circuit.
(a) If customers demand the data-circuits with a mean holding time of
2 hours and mean arrival rate of 6.5 per hour, calculate the traffic
volume in Erlang. Furthermore, using the graph in Figure 1, estimate
the blocking probability that customers will observe. Explain how you
have achieved your answer and what assumptions are required.
A=hL
A is the traffic in Erlang
h is the holding time
L is the arrival rate
What is the traffic volume?
A = h * L = 2 * 6.5 = 13 what are the units of this in SI units?
Units of A are hours * hours^-1 = hours/hours !!!! No units
With 25 circuits, what is the blocking probability?
We look at the E=13, and the T=25 lines, where they intersect gives
us the blocking probability.
Answer is 1e-03 = 1 X 10^-3 = 0.001 = 0.1%
Assumptions: all the customers are acting independently.