Stop-and-Wait-ARQ

Question 1

On a wireless link, the probability of packet error is 0.2. A stop-and-wait protocol is used to transfer data across the link. The channel condition is assumed to be independent from transmission to transmission. What is the average number of transmission attempts required to transfer 100 packets?

A
100
B
125
C
150
D
200
Computer-NetworksStop-and-Wait-ARQGATE 2006-IT
Question 1 Explanation: 
Total no. of re-transmissions for one frame, in general, is 1/(1-P) where P is probability of error.
So here it would be for one frame = 1/(1-0.2) = 1/0.8
So for 100 frames = 100/0.8 = 125
Question 2

A link has a transmission speed of 106 bits/sec. It uses data packets of size 1000 bytes each. Assume that the acknowledgement has negligible transmission delay, and that its propagation delay is the same as the data propagation delay. Also assume that the processing delays at the nodes are negligible. The efficiency of the stop-and-wait protocol in this setup is exactly 25%. The value of the one-way propagation delay (in milliseconds) is ___________.

A
12
B
13
C
14
D
15
Computer-NetworksStop-and-Wait-ARQGATE 2015 [Set-2]Video-Explanation
Question 2 Explanation: 
Given, B = 106bps
L = 1000
η = 25%
Tp = ?
In stop-and-wait, η = 1/1 + 2a
⇒1/4 = 1/1 + 2a ⇒ 1 + 2a = 4
2a = 3; a = 32
Tx = L/B = 8×103/106 = 8ms
Tp/Tx = 3/2; 2Tp = 3Tx
2Tp = 24ms
Tp = 12ms
There are 2 questions to complete.

Access quiz wise question and answers by becoming as a solutions adda PRO SUBSCRIBER with Ad-Free content

If you have registered and made your payment please contact solutionsadda.in@gmail.com to get access