ACE test_series

Question

Is this question and solution both are wrong?

Comments

Both question and its solution is correct. Although, they haven't explained the solution clearly enough. Anyways, correct answer is C. What did you get?

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my doubt was if they have given delay for B, D, E are 6,3,5 respectively.

Then why in diagram they mentioned delays as 2, 3 ,1 ?

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Delays can change over time and they must be checked before each iteration of routing algorithm. For example, B directly to A has also changed from 4 in the diagram to 15(as given in B's distance vector).

Answer 1

here answer is C....bro how i solve is  CB,CD,CE.....now vet at c will be min of (CB+B-TO-NEXT-PATH,CD+D-TO-NEXT-PATH,CE+E-TO-NEXT-PATH);

and you can find it....

Comments

thank you

Answer 2

Question is fine and the answer is C.

C's present routing table is like - (∞,6,0,3,5,∞) [Assuming its second iteration]

On receiving B as -(15,0,18,12,16) & D as- (16,12,6,0,9,10) & E as- (17,16,13,19,0,14)

C will attempt to minimize its delays to A-

Using B For A, delay of C-B=6 & B-A=15, total=6+15=21, Since ∞>21, Update C's table as  (21,6,0,3,5,∞)

Using D For A, delay of C-D=3 & D-A=16, total=3+16=19, Since 21>19, Update C's table as  (19,6,0,3,5,∞)

Using E For A, delay of C-E=5 & E-A=17, total=5+17=22, Since 19<22, No Update in C's table (19,6,0,3,5,∞)

Similarly minimize delays to F-

Using B For F, delay of C-B=6 & B-F=16, total=6+16=22, Since ∞>22, Update C's table as  (19,6,0,3,5,22)

Using D For F, delay of C-D=3 & D-F=10, total=3+10=13, Since 22>13, Update C's table as  (19,6,0,3,5,13)

Using E For F, delay of C-E=5 & E-F=14, total=5+14=19, Since 13<19, No Update in C's table (19,6,0,3,5,13)

Final table- (19,6,0,3,5,13)

P.S- I have skipped checking for B,D,E as they are already minimum, but they should be checked in each iteration.

Comments

Thanks for such detailed answer , my doubt was if they have given delay for B, D, E are 6,3,5 respectively.

Then why in diagram they mentioned delays as 2, 3 ,1 ?

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See, before updating the routing table, you would have to check whether they are talking about delays or link distance. As you can very clearly see from tables of either B, D or E that their immediate neighbours have values more than the actual link distance(from the graph) in their respective routing table.

eg- Link distance for B-A=4 but in its routing table it's 15(check for others).This is the clue.Moreover, why would they give information about delays to B, D and E?

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thank you for help

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well as long as exam is concern there is no need to solve the whole question , a,b,d are definetly wrong as they say cost from c to c is not zero