Challenge 1: Feedback
The aim of this presentation is to demonstrate one correct approach to
solving the challenge,
Presentation Structure:
Typical Answers
Collecting Data from the Question
Applying the Formulae
Answers Analysis
Fast and Furious
Author: L.Saliou. Chall 1 (1)
Challenge 1: Typical Answers
Challenge 1
45
40
35
30
Vote
25
20
15
10
5
0
A4 B1 C1 D6 E1 E3 E6 F1 F2 F3 F4
Location
Author: L.Saliou. Chall 1 (2)
Challenge 01: Collecting Data from the Question
• The Question was:
« A fault has occurred on a token ring network with a radius of 30m. It
uses fibre optic cables which propagate the pulses at one-third of the
speed of light. If it takes 1 µs (1E-6) for the pulse to be sent from
Node A, and be received back, estimate the sector that contains the
fault for the ring given in the Figure. Also estimate the total time that
the pulse will take to go round the ring »
• Key words:
– Radius of 30m
– 1/3 of the speed of light
– Time: 1µs (from Node A and back)
Author: L.Saliou. Chall 1 (3)
Challenge 01: Applying the Formulae
• Formulae given in the challenge are:
– d = s*(t/2)
– P=2*r*π
• The speed of light is assumed to be: 3E8 m/s hence here the speed
would be:
–
s = 1E8 m/s
• Hence:
– d = 1E8 * (1E-6) / 2 = 0.5 * E(8 + (-6)) = 0.5E2 = 50 meters
– P = 2 * 30 * 3.14 = 60 * 3.14 = 188.4 meters
Author: L.Saliou. Chall 1 (4)
Challenge 01: Applying the Formulae
• The best to work out the position is to determine the percent of the
perimeter covered by the pulse before reaching the break. Hence:
– As 188.4 meters represents 100% of the perimeter
– 50 meters represents: location = (50 / 188.4) * 100 = 26%
• Taking the axis (O-A) as the origin it gives us the result F3
• The time to go all around the circle is:
– T = d/s = 188.4 / 1E8 ≈ 2µs
Author: L.Saliou. Chall 1 (5)
Challenge 01: Applying the Formulae
Node A
6
5
4
20
B
0
3
2
1
A
B
C
D
E
F
Author: L.Saliou. Chall 1 (6)
Challenge01: Answers Analysis
Assuming that the perimeter is 188.4 meters
Wrong answers due to misreading
A4: misreading of the question, the full speed of light was assumed
B1, E1: wrong assumption of half the speed of light
C1: half the speed of light was assumed (speed assumed in the example)
D6, E6: the answer was not 5 meters; misleading power of ten
F1, F2: neither a third or an half of the speed of light was assumed
F4: wrong assumption of a third of the light speed
Author: L.Saliou. Chall 1 (7)
Challenge01: Fast & Furious
Assume the correct distance and π is 3
Then the perimeter becomes 180 meters which is close to 200
meters
Hence 50 div 200 = 25
In percent → 25%
The answer: F2 or F3
As 180 is smaller than 200 the pulse has covered more than 25%
The good answer is F3
Author: L.Saliou. Chall 1 (8)
Challenge 01: Fast & Furious
Assuming time for the pulse to go all around the circle being 2µs
Assuming a break (pulse going in and back) only 50% can be covered
As the half the time is given (1µs) hence the covering is half of 50%
Hence the pulse has covered 25% → F2 or F3
The results are consistent
Author: L.Saliou. Chall 1 (9)