 # Computer Networking Management

Autor:   •  March 8, 2011  •  Essay  •  8,083 Words (33 Pages)  •  2,852 Views

Page 1 of 33

a) For each segment, making any necessary assumptions, calculate the following and plot the data on a graph:

• An appropriate timeout interval for use when transmitting the next TCP segment.

Estimated RTT =

(1-a)3*Sample RTT(4)+a*(1-a)2*Sample RTT(3)+a8(1-a)*Sample RTT(2)+a*Sample RTT(1)

We can calculate Estimated RTT by using the above calculation Formula

If α = 0.1 in this problem

We can derive exponentially weighted moving average (EWMA) of RTT

For First 10 segments:

1) (0.9)9 x 127 + (0.1) x (0.9)) 8 x 134 + (0.1) x (0.9)) 7 x 121+ (0.1) x (0.9)) 6x 139+ (0.1) x (0.9)) 5 x 139+ (0.1) x (0.9)) 4 x 131 + (0.1) x (0.9)) 3 x 124 + (0.1) x (0.9)) 2x 122 + (0.1) x (0.9)) 1x 128

+ (0.1) x130

For Second 10 segments:

(0.9)9 x 139 + (0.1) x (0.9)) 8 x 134 + (0.1) x (0.9)) 7 x 123+ (0.1) x (0.9)) 6x 291+ (0.1) x (0.9)) 5 x 137+ (0.1) x (0.9)) 4 x 141 + (0.1) x (0.9)) 3 x 134 + (0.1) x (0.9)) 2x 126 + (0.1) x (0.9)) 1x 139

+ (0.1) 267

Figure: Segment vs. EWMA

For Third 10 segments:

(0.9)9 x 127 + (0.1) x (0.9)) 8 x 134 + (0.1) x (0.9)) 7 x 121+ (0.1) x (0.9)) 6x 139+ (0.1) x (0.9)) 5 x 139+ (0.1) x (0.9)) 4 x 131 + (0.1) x (0.9)) 3 x 124 + (0.1) x (0.9)) 2x 122 + (0.1) x (0.9)) 1x 128

+ (0.1) x130

For reference, alpha = .1

• The variability of RTT (sometimes referred to as Dev RTT).

Estimated RTT =54.96

Sample RTT =127

Difference = Sample RTT – Estimated RTT

=>127-54.96

=> 54.96

As per Jacobson/Karels Algorithm,

Deviation = Deviation + d ( |Difference| - Deviation)), where d is a fraction between 0 and 1

If, Deviation = 5, d= 0.01

 5 + 0.01 ( 54.96 - 5))

 5.4996

 Deviation =5.4996

• An appropriate timeout interval for use when transmitting the next TCP segment.

First need to Measure Sample RTT for each segment/ACK

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