Faculty of Information and
Engineering Technology
Dr. Tallal Elshabrawy
Bar Code
Internet (NETW 503)
Winter 2015
Midterm Examination
Oct. 22nd 2015
Please read carefully before proceeding.
1. The duration of this exam is 2 hours
2. Only calculators are permitted for this exam
3. This exam booklet contains 13 pages including this one.
4. Two extra sheets of scratch papers are attached
5. Two Pages of Formula Sheet are attached at end (Do Not Remove)
6.
Good Luck!
Marks:
Problem
Number
Possible Marks
Final Marks
1
2
3
4
5
Total
10
10
15
15
20
70
Problem 1:
a) Suppose a router is used to interconnect three different networks: Network 1,
Network 2, Network 3
(6 Marks)
i. List the layers that would be supported by the router
ii. How many MAC addresses does the router have?
iii. How many IP addresses does the router have?
iv. Suppose a computer is moved from Network 1 to Network 2. Does its MAC
address need to change?
v. Suppose a computer is moved from Network 1 to Network 3. Does its IP
address need to change?
b) Which transport layer protocol does the following application layer protocols
use
(4 Marks)
i. SMTP (Simple Mail Transfer Protocol)
ii. RTP (Real-Time Protocol)
iii. HTTP (Hypertext Transfer Protocol)
iv. DNS (Domain Name Service)
2
Problem 2:
The text below shows the reply sent from the server in response to the HTTP GET
message in the question above. Answer the following questions, indicating where
in the message below you find the answer.
(10 Marks)
i. Was the server able to successfully find the document or not? What time
was the document reply provided?
ii. When was the document last modified?
iii. How many bytes are there in the document being returned?
iv. What are the first 5 bytes of the document being returned? Did the server
agree to a persistent connection?\
3
Problem 3:
You have clicked on http://www.nytimes.com. The figure below shows 8 captured
packets that are either transmitted or received by your PC since you have clicked
on the web link.
(15 Marks)
i. What is the IP address of the HTTP Client.
ii. What is the IP address of the DNS Server.
iii. What is the IP address of the HTTP Server.
iv. What is the port number for the TCP connection.
4
v. Fill in the table below
Packet
No
Indicate whether this
packet is transmitted or
received by your PC
Explain what does this packet represent
1
2
3
4
5
6
7
8
vi. Fill in the following details for the ninth packet to follow the eight packets
shown in the figure.
Source
Destination
Protocol
5
Problem 4:
Consider distributing a file of F = 20 Gbits to N peers, as shown in the following
figure. The server has an upload rate of us= 40 Mbps, and each peer has a
download rate of di = 4 Mbps and an upload rate of u.
For N = 100 and u = 500 Kbps, evaluate the distribution time for both client-server
distribution and P2P distribution.
(15 Marks)
6
7
Problem 4:
Consider a Network for which there is an institutional LAN network connected to
the Internet. The access link to the Internet has a rate of 8 Mbps and the
institutional LAN rate is 100 Mbps. Suppose that the average web page size is
500,000 bits composed of 10 objects. The average request rate from the
institution’s browsers to the origin servers is 10 web page requests per second.
Also suppose that the amount of time it takes from when the router on the
Internet side of the access link forwards an HTTP request until it receives the
response is 2 seconds on average.
The total average response time for any objects is modeled as the sum of the
average access delay (that is, the delay from Internet router to institution router)
and the average Internet delay and the average LAN delay.
- For the average access delay, use Δ / (1 – Δβ), where Δ is the average
time required to send an object over the access link and β is the arrival
rate of objects to the access link.
- For the LAN delay assume that it is equal to the transmission time of an
object
(20 Marks)
i. In order to download one web page, what would be the average download time
if Non-persistent HTTP with no parallel TCP connections?
8
9
ii. Now suppose a cache is installed in the institutional LAN. Suppose the miss rate
is 0.4. In order to download one web page, what would be the average
download time if Non-persistent HTTP with no parallel TCP connections?
10
11
Extra Sheet 1:
12
Extra Sheet 2:
13