WorksheetsComputer Networks-Model Exam-I_Part-B
Total questions: 10
Worksheet time: 20mins
Name
Class
Date
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
2.
Compute the fraction of the bandwidth that is wasted on overhead (headers and retransmissions) for a protocol on a heavily loaded 50 Kbps satellite channel with data frames consisting of 40 bits header and 3960 data bits. Assume that the signal propagation time from the earth to the satellite is 270 msec. ACK frames never occur. NAK frames are 40 bits. The error rate for data frames is 1% and the error rate for NAK frames is negligible.
a)
0.0121
b)
0.0212
c)
0.0199
d)
0.0171
3.
Consider 1 Mbps error free line. The maximum frame size is 1000 bits. New packets are generated about 1 sec apart. The time out interval is 10 msec. If the ack timer is eliminated. How many times the average message be transmitted?
a)
only once
b)
twice
c)
thrice<br />
d)
cant say
4.
What is the effect on line utilization if we increase the number of frames for a constant message size?
a)
Lower line efficiency
b)
Higher line efficiency
c)
No change in line efficiency
d)
No relation between line efficiency and frame size
5.
In what protocols is it possible for the sender to receive an acknowledgement for a packet that falls outside its current window?
a)
Stop and Wait
b)
Selective Repeat
c)
Go back N
d)
All of the above
6.
A device has two or more IP Addresses, the device is called
a)
Workstation
b)
Router
c)
Gateway
d)
All of these
7.
Consider the effect of using slow start on a line with a 10 msec RTT and no congestion. The receiver window is 24 KB and the maximum segment size is 2 KB. How long does it take before the first full window can be sent?
a)
110msec
b)
90msec
c)
85msec
d)
95msec
8.
Consider an instance of TCP’s Additive Increase Multiplicative Decrease (AIMD) algorithm where the window size at the start of slow start phase is 2 MSS and the threshold at the start of first transmission is 8 MSS. Assume that a time out occurs during the fifth transmission. Find the congestion window size at the end of tenth transmission
a)
8 MSS
b)
14 MSS
c)
7 MSS
d)
12 MSS
9.
The intermediate routers between source and destination need the following information in IP header-
a)
Version
b)
Protocol
c)
Identification Number
d)
Source IP Address
e)
all of the mentioned
10.
Fragmentation of a datagram is needed in-
a)
Datagram circuit only
b)
Virtual circuit only
c)
Both (A) and (B)
d)
None
100 %
