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Q1
2 Points
Indicate whether this statement is true or false:
Packet switching provides more predictable performance than does
circuit switching because packet switching is more efficient than
circuit switching.
Q2
2 Points
Indicate whether this statement is true or false:
All connection-oriented transport layer protocols reserve network
resources along the path from source to destination before
establishing a connection.
Q3
2 Points
Indicate whether this statement is true or false:
HTTP cookies can be used to track the browsing patterns of a
particular user on a particular website.
true
false
true
false
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Q4
4 Points
In Q4.1 - Q4.4, indicate all types of delay which are affected by the
transmission speed of a router:
Q4.1
1 Point
transmission delay in that router
Q4.2
1 Point
propagation delay in inbound links to that router
Q4.3
1 Point
propagation delay in outbound links from that router
true
false
yes
no
yes
no
yes
no
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Q4.4
1 Point
queuing delay in that router
Q5
2 Points
Consider a video streaming application that uses HTTP and that uses
buffering in the client side of the application.
Indicate whether this statement is true or false:
A drawback of this technique is that when the client side buffer of the
application is full, newly arriving packets will be dropped and some
parts of video frames will be lost.
Q6
2 Points
Indicate whether this statement is true or false:
The POP3 protocol is used by some email servers to maintain a
central email repository that can be accessed from multiple
machines.
yes
no
true
false
true
false
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Q7
4 Points
In Q7.1 - Q7.4, indicate all protocols below which are stateless
application layer protocols:
Q7.1
1 Point
UDP
Q7.2
1 Point
FTP
Q7.3
1 Point
HTTP
Q7.4
1 Point
POP3
yes
no
yes
no
yes
no
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Q8
2 Points
A source host S communicates with a destination host D through an
intermediate router R.
One packet is sent from S to D.
How many times does the packet has to visit the network layer and
the data link layer during the transmission from S to D?
Q9
2 Points
When a host receives a TCP packet, what field in the packet is not
used to determine the socket to handle this packet?
yes
no
The packet visits the network layer 4 times and visits the data link
layer 4 times.

The packet visits the network layer 4 times and visits the data link
layer 3 times.

The packet visits the network layer 3 times and visits the data link
layer 4 times.

The packet visits the network layer 3 times and visits the data link
layer 3 times.

The packet visits the network layer 2 times and visits the data link
layer 4 times.

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Q10
6 Points
In Q10.1 - Q10.6, indicate whether the blocking probability of calls in
a circuit-switched networks depends upon each quantity below:
Q10.1
1 Point
the maximum permissible loss rate of packets
Q10.2
1 Point
the call arrival rate
Q10.3
1 Point
the bandwidth of the trunks along the route
Destination MAC address
Source IP Port
Destination IP Address
Destination Port
true
false
yes
no
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Q10.4
1 Point
the burstiness of the voice stream
Q10.5
1 Point
the average duration of a call
Q10.6
1 Point
the average delay through each switch
Q11
24 Points
A source host S communicates with a destination host D through an
intermediate router R.
yes
no
yes
no
yes
no
yes
no
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S and R are connected by a 200 km link with a transmission rate of
40 Mbps.
R and D are connected by a 400 km link with a transmission rate of
80 Mbps.
The propagation speed on both links is m/s.
The source host S transmits two files to the destination host D. Each
file is 10 KB. The source host S uses neither flow control nor
congestion control.
The router R does NOT use cut-through forwarding. There is no
traffic passing through R other than the two files.
Q11.1
6 Points
What is the transmission delay of one file at the source host S?
q11.jpeg Download
2 ∗ 108

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Q11.2
6 Points
What is the propagation delay between S and R?
q11.jpeg Download
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Q11.3
6 Points
At what time does the destination host D completely receive the 2nd
file?
q11.jpeg Download
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Q11.4
6 Points
Assume now that the transmission rate of the link between R and D
is 20 Mbps. At what time does the destination host D completely
receive the 2nd file?
q11.jpeg Download
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Q12
24 Points
A source host S communicates with a destination host D through an
intermediate router R1 and another intermediate router R2. The
source host transmits a sequence of packets.
The probability of packet loss at the router R1 is , the probability of
packet loss at router R2 is , and packet losses at router R1 are
independent of packet losses at router R2.
p
p
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Q12.1
8 Points
If a packet is transmitted by source S, what is the average number of
hops until the packet is either dropped at a router or received at
destination D?
q12.jpeg Download
Q12.2
8 Points

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If a packet is dropped at either router R1 or router R2, then after a
timeout the source S will retransmit the packet.
What is the average number of transmissions by source S before a
packet is successfully received at destination D?
q12.jpeg Download
Q12.3
8 Points

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What is the average number of hops from the first transmission of a
packet at source S until it is successfully received at destination D?
q12.jpeg Download
Q13
24 Points
This problem will compare circuit switching and packet switching.
Consider a single link with capacity 10 Mbps. There are 15 users
that occasionally transmit traffic through this link.

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Each user is active for 6 sessions per hour, with each session lasting
3 minutes. During each session, each user transmits bursty traffic in
packets of 10 kb, with a peak rate of 200 packets/second and an
average rate of 100 packets/second.
When there is blocking, the formula for blocking probability is
, where = the average number of active sessions
and = the capacity of the link expressed as a multiple of the
bandwidth required for each session.
When there is queuing, the formula for queuing delay is ,
where = the average arrival rate at the link (in packets per second)
and where = the capacity of the link (in packets per second).
Q13.1
4 Points
For parts 13.1-13.3, assume the link uses circuit switching. What is
the traffic load on the link?
No files uploaded
Q13.2
4 Points
Give an expression for the blocking probability.
No files uploaded
Q13.3
4 Points
What is the queuing delay entering the link?
No files uploaded
Q13.4
4 Points
1+y+y /2!+...+y /N !2 N
y /N !N y
N
– d−c
1
d
1
c
d



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For parts 13.4-13.6, assume the link uses packet switching. What is
the traffic load on the link?
No files uploaded
Q13.5
4 Points
Give an expression for the blocking probability.
No files uploaded
Q13.6
4 Points
What is the queuing delay entering the link?
No files uploaded



GRADEDMidterm
STUDENT
Hongshan Chen
TOTAL POINTS
44 / 100 pts
QUESTION 1
(no title) 0 / 2 pts
QUESTION 2
(no title) 2 / 2 pts
QUESTION 3
(no title) 2 / 2 pts

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QUESTION 4
(no title) 3 / 4 pts
4.1 (no title) 1 / 1 pt
4.2 (no title) 0 / 1 pt
4.3 (no title) 1 / 1 pt
4.4 (no title) 1 / 1 pt
QUESTION 5
(no title) 0 / 2 pts
QUESTION 6
(no title) 2 / 2 pts
QUESTION 7
(no title) 3 / 4 pts
7.1 (no title) 1 / 1 pt
7.2 (no title) 1 / 1 pt
7.3 (no title) 1 / 1 pt
7.4 (no title) 0 / 1 pt
QUESTION 8
(no title) 0 / 2 pts
QUESTION 9
(no title) 2 / 2 pts
QUESTION 10
(no title) 4 / 6 pts
10.1 (no title) 0 / 1 pt
10.2 (no title) 0 / 1 pt
10.3 (no title) 1 / 1 pt
10.4 (no title) 1 / 1 pt
10.5 (no title) 1 / 1 pt
10.6 (no title) 1 / 1 pt
QUESTION 11
(no title) 19 / 24 pts
11.1 (no title) 6 / 6 pts
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11.2 (no title) 6 / 6 pts
11.3 (no title) 6 / 6 pts
11.4 (no title) 1 / 6 pts
QUESTION 12
(no title) 7 / 24 pts
12.1 (no title) 0 / 8 pts
12.2 (no title) 7 / 8 pts
12.3 (no title) 0 / 8 pts
QUESTION 13
(no title) 0 / 24 pts
13.1 (no title) 0 / 4 pts
13.2 (no title) 0 / 4 pts
13.3 (no title) 0 / 4 pts
13.4 (no title) 0 / 4 pts
13.5 (no title) 0 / 4 pts
13.6 (no title) 0 / 4 pts

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