ECEC357 Introduction to Computer Networks (Fall 201415)
Practice Midterm Exam
Time: 1 hour , 15 minutes
Max Points: 30
Answer all questions each carries 5 points
Q1
Using Shannons theorem, calculate the maximum bit rate that can be achieved on a fiber o
Ch 3  Worked_out_Example 3.3
Problem:
Calculate the timeouts after each SampleRTT given the following, using the Exponential
Weighted Moving Average (EWMA) formula:
Initial EstimatedRTT = 120 ms
First SampleRTT = 132 ms
Second SampleRTT = 114 ms
Third Sa
Ch 3  Worked_out_Example 3.3
Problem:
Calculate the timeouts after each SampleRTT given the following, using the Exponential
Weighted Moving Average (EWMA) formula:
Initial EstimatedRTT = 120 ms
First SampleRTT = 132 ms
Second SampleRTT = 114 ms
Third Sa
Ch 1  Workedout Example 5
Problem:
Consider a closed loop network with bandwidth 100 Mbps and velocity of
propagation 2 X 10 8 m/s. What would be the circumference of the ring to exacly
contain a 250 byte packet assuming nodes do not introduce a delay?
C357 Worked Out Example 1.5 (Bandwidth Delay Product)
Problem Statement:
A copper link A to B 460 Km long is being used to transmit a packet of 1000 Bytes at 10 Mbps.
(i)
(ii)
(iii)
What is the maximum number of bits that the link can hold at any time?
W
C357 Worked Out Example 1.6 (Bit Width)
Problem Statement
Solve Worked Out Example 1.5 from bit width considerations
Solution:
(i)
Bit width = s/R = 2.3*10^8 m/sec / 10*10^6 bits/sec = 23 m /bit
Length of the link = 460 Km
Therefore, No of bits on the li
Ch 1  Workedout Example 4
Suppose 2 hosts A and B separated by 10,000 Kms and are connected by a direct link at 1
Mbps. The propagation speed is 2.5*10^8 meters/sec. A file of size 400,000 bits needs to
be sent from A to B.
a. How long does it take to s
Ch 1  Workedout Example 2
Problem
Calculate the channel capacity of a fiber optic link operating at a wavelength
of 1300 nm with a spread of 10 nm on either side. Assume S/N = 30 db
Solution
The two extreme wavelengths are 1290 nm and 1310 nm
Find the f
C357 Worked Out Example 1.3 (Multihop Links)
A. Switches not storeandforward (same bit rate on all links)
5000 [email protected] Mbps
AS1S2B
400 Km fiber
900 Km wireless
230 Km Copper
Propagation delay = 400*10^3/2*10^8 + 900*10^3/3*10^8 +230810^3/2.3*10^8 se
Ch 1  Workedout Example 1
Problem:
What would be the channel capacity of a channel with 3 KHZ analog bandwidth
(i) if it was noise free using binary signalling
(ii) if it was noise free using 16 level signalling
(ii) if it was noisy with S/N = 30 db
Sol
TCP's Congestion Window Size
o An intuitive definition of the Congestion Window Size is the amount of
data that the sender can inject into the network without causing
congestion in the network.
o Notice that this amount of data varies over time (it depen
Question 4 (TCP Congestion Control) 6 points: Assuming TCP Reno is the protocot
experiencing the behavior shown in ﬁgure betav, ansiver the foitowing questions. In at!
cases, you shouid provide a short discussion justiﬁing your answer. 9/6 points for ea
Clientserver architecture
server:
alwayson host
permanent IP address
data centers for scaling
clients:
client/server
communicate with server
may be intermittently
connected
may have dynamic IP
addresses
do not communicate
directly with each other
Applic
System Performance
1
Performance Limitations
Two primary performance limitations
Attenuation limited length
Optical signal is too low to receive the correct data
Depends on:
Fiber attenuation
Receiver sensitivity
Transmitted power
Dispersion limited
Ch 3  Worked_out_Example 3.3b
Problem:
Calculate the timeouts after each SampleRTT given the following, using the more
complex formula including deviation:
Initial EstimatedRTT = 120 ms
Initial Deviation = 16 ms
First SampleRTT = 132 ms
Second SampleRTT
Ch 3 Worked Out Example 3.4
Consider transferring a large file of L bytes from Host A to Host B. Assume MSS=536 bytes
a. What is the maximum value of L such that TCP sequence numbers are not exhausted?
b. For the L you obtain in part (a) how long will it
Ch3 Worked out Exampleg.2
The figures below show how TCP recovers from various types of loss situations. In each, the
sender
starts with seq no =92 and tries to send two segments to the receiver the first segment contains g
bytes
of data and the second s
Ch 3  Worked_out_Example 3.3b
Problem:
Calculate the timeouts after each SampleRTT given the following, using the more
complex formula including deviation:
Initial EstimatedRTT = 120 ms
Initial Deviation = 16 ms
First SampleRTT = 132 ms
Second SampleRTT
Ch 3 Worked Out Example 3.4
Consider transferring a large file of L bytes from Host A to Host B. Assume MSS=536
bytes
a. What is the maximum value of L such that TCP sequence numbers are not
exhausted?
b. For the L you obtain in part (a) how long will it
ECEC357 Quiz # 3 Solutions (11/06/2014)
Time: 30 mins
Max Points: 10
Q1
Client A wants to establish a TCP connection with server B . The initial sequence
number chosen by A is 66. B agrees to establish the connection with initial
sequence number 94. In t
ECEC357 Quiz # 4 Solutions
Time: 30 mins
Max Points: 10
Q1
In TCP flow control, the size of the Receive Buffer is 512 bytes and that of the
Sending Buffer is 768 bytes. The values of the various pointers are as follows:
LastByteRead = 384
LastByteAcked =
C357 Quiz # 5 Solutions
Time: 30 mins
Max Points: 10
Answer all questions
Q1
Contrast ClientServer architecture with PeertoPeer architecture with respect to
any 4 features. Each feature must be present in one architecture , but not in the
other.
(2)
(i
C357 Homework Assignment # 1
Do the following problems at the end of Chapter 1 in 6 th Ed :
Q1. Problem R18
Q2. Problem R19
Q3. Problem P5
QUIZ 1
Q4. Problem P6
Q5 Problem P10
Q6. Problem P24
Q7 Problem P12
Q8 Problem P13
Q9. Problem P25
Q10. Problem P26
Answers to HW1 Problems
R18
14 ms
R19
500 Kbps, 64 secs, 320 secs
P5
96 mins, 94 mins and 48 secs
P6
g. 536 Km
P10
64 ms
P24
37 days, Fedex is better
P12
27 ms
P25
a. 160000 bits
b. 160000 bits
d. 125 m
P26
12.5 bps
P27 a. 80 milion bits
b. 800,000 bits
c
Band Frequency Range Origin of Name
I
up to 200 MHz
Unknown
G
200 to 250 MHz
Unknown
P for "previous", as the British used the band
P
250 to 500 MHz
for the earliest radars, but later switched to
higher frequencies.
L
0.5 to 1.5 GHz
L for "long" wave.
S f
Ch 3

Worked Out Example 9"1
In this example, client sets up a TCP connection
with server B with a initial sequence number
x=41. The initial sequence number y provided by the server for this connection is 78. The 3way
handshake is as shown below. The 2
Ch 4_Worked_Out_Example 2.doc
Problem Statement:
A class C network has the IP address 200.1.1. For m 4 subnets with the
following numbers of hosts in each:
Subnet A 72 hosts
Subnet B 35 hosts
Subnet C 20 hosts
Subnet D 18 hosts
Solution:
A needs 7 bits (7
Ch 4 Worked_Out_Example 1.doc
This example shows how forwarding is done in a datagram network.
The table below is a routing table using CIDR. State to which interface datagrams
addressed to the following destination addresses will be delivered.
(a) C4.5E.