It\'s a question from computer networking course (Topic: DNS). Can anyone provid

Question

It's a question from computer networking course (Topic: DNS).

Can anyone provide me with a full detialed answer?

10. [10 pts.] We wish to compare the response time to a DNS query in an institutional network that uses a local DNS server to that of an institutional network that doesn't. Assume that the local DNS server has a hit rate of 0.8. Also assume that the average round-trip delay within the institutional LAN is about TLAN 0.1 ms, and that the round-trip delay in the Internet is about Tint-1 s. a. What is the total DNS resolution delay, To, for the case of an institution that doesn't use a local DNS server? b. What is the total DNS resolution delay. Ti, for the case of an institution that uses a local DNS server? c. For what value of the ratio E1-TLAN/TInt does To and Ti come to within 10% of one another ie. the ratio €2 = T/T) = 0.9?

Explanation / Answer

10.

TLAN = 0.1ms = 0.1*10-3s = 10-4s

TINT = 1s

Hence, total DNS resolution delay, T0= TINT = 1s

Since hit rate = 0.8

Hence, total DNS resolution delay, T1= (0.8*TLAN) + (1-0.8) *TINT

Equation 2:         T1= (0.8*TLAN) + 0.2 *TINT

Doing Equation 2/Equation1

T1/ T0= (0.8*TLAN+ 0.2 *TINT)/ TINT

Hence, for 0.875, T0 and T1 come within 10% of one another.10.

TLAN = 0.1ms = 0.1*10-3s = 10-4s

TINT = 1s

Hence, total DNS resolution delay, T0= TINT = 1s

Since hit rate = 0.8

Hence, total DNS resolution delay, T1= (0.8*TLAN) + (1-0.8) *TINT

Equation 2:         T1= (0.8*TLAN) + 0.2 *TINT

Doing Equation 2/Equation1

T1/ T0= (0.8*TLAN+ 0.2 *TINT)/ TINT

Hence, for 0.875, T0 and T1 come within 10% of one another.

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