1. Processes in network identify each other by an abstract locator called ______
Port address
2. Which flag is used in the first step of connection termination phase of TCP?
FIN
3. Which of the following is true regarding the characteristics of UDP? a. Implements mechanisms
for reliable delivery b. Does not implement mechanisms for flow control.
Only b is true
4. What mechanism in TCP involves preventing too much data from being injected into the
network?
Congestion control
5. In the original algorithm for adaptive retransmission in TCP, EstimatedRTT and TimeOut value is
computed as _________(Assume α is the smoothing parameter, SampleRTT is the difference
between these two times in receiving the current and previous acknowledgment )
EstimatedRTT = α×EstimatedRTT+(1−α)×SampleRTT , TimeOut = 2×EstimatedRTT
6. When the fast retransmit mechanism signals congestion, rather than drop the congestion
window all the way back to one packet and run slow start, it is possible to use the ACKs that are
still in the pipe to clock the sending of packets. This mechanism is called ____
Fast recovery
7. Congestion avoidance mechanism in which a single congestion bit is added to the packet header
is called _____
DECbit
8. Consider the congestion window size for a TCP connection when a timeout occurs be 16 KB. The
round trip time of the connection is 50 msec and the maximum segment size used is 2 KB. The
size of the congestion window in terms of Maximum Segment Size(MSS) is _________.
8 MSS
9. Which application layer protocol runs in port number 53?
DNS
10. The transport layer protocol which is used to improve the performance of connection-oriented
web application is called ______
QUIC
11. The application layer protocol that helps in the transfer of flies from one computer to another is
___
FTP
12. An adaptive streaming protocol that enables high quality streaming of media content over the
Internet is ____
DASH
13. A simple protocol to retrieve email from server with minimal error is ____
POP 3
14. Which of the following statement(s) is/ are not correct? I. TCP connections are full duplex II. TCP
has no option for selective acknowledgment III. TCP connections are message streams
Only II and III
15. What extra component is added with the TCP and UDP header fields to verify the message
delivery between two end points?
pseudoheader
1. What happened at time 20?
Ans: timeout
2. What happened at time 10?
Ans: duplicate acknowledgement,multiplicative decrease
3. When is the Congestion avoidance phase of slow start?
Ans: 10-20,34-44,after 44
4. What congestion control mechanism is followed between time 10-20?
Ans: Additive increase
5. What congestion control mechanism is followed at time 20?
Ans: Slow start
6. The protocol value of UDP in IP header is ____
Ans: 17
7. What extra component is added with the TCP and UDP header fields to verify the message
delivery between two end points?
Ans: pseudoheader
8. The size of the source and destination port fields is ____
Ans: 2 bytes
9. The size of the sequence number and the advertised window fields in TCP header are ___
and ____ respectively.
Ans: 4 bytes, 2 bytes
10. The algorithms used to establish TCP connection is called
Ans: Three-way handshaking
What is the congestion window size at 4th RTT?
Ans: 16
Identify the time periods when TCP slow start is operating(more than one answer possible)
Ans: 0-4,7-10
Identify the time periods when TCP congestion avoidance is operating (AIMD).
Ans:4-6,10-14,15-17,6-9
At the 6th RTT, is the segment loss detected by_______
Ans:timeout
What is the initial value of ssthreshold, before the first congestion avoidance interval?
Ans: 16
What is the value of ssthreshold, after the first congestion avoidance interval?
Ans: 9
What is the value of ssthreshold, after the second congestion avoidance interval?
Ans: 6
At the 14th RTT, is the segment loss detected by
Ans: duplicate ack
Assuming a packet loss is detected after the 17th RTT by the receipt of a triple duplicate ACK, what will
be the values of the congesion-window size and of ssthreshold?
Ans: 4,4
1. TCP/IP model follows
a. Connection oriented approach
b. Connectionless approach
c. Connection oriented over connectionless approach
d. Connectionless over connection oriented approach
2. Flag bit used for establishing a connection is
Ans: SYN
3. The client sends the following information to the server during the initiation of 3-way
handshaking
Ans: SYN, Sequence number=x
4. The sequence number of the TCP segment starts with ___
Ans: random number
5. One of the important part of the TCP message includes ________
a.
b.
c.
d.
Information about application which generated that message
Information about machine which generated that message
Information about user who generated that message
Information about the status of that message
6. TCP segment is verified by ______________
a.
b.
c.
d.
The next network layer
The previous application layer
The receiving TCP layer
The TCP layer of the next immediate router
7. The core protocol used in tcp is __
Ans: sliding window
8.
TCP is also called as ______
Ans: byte-oriented protocol
9.__________ is the address used to by the TCP to identify the target process.
Ans: port number
10.
The size of the source address in a UDP header is__
Ans:16 bits
11. _________is used to reassemble the message at the receiving end if the segments are
received out of order.
a. Sequence Number
b. Advertised Window
b. Sender Window
c. Receiver Window
12. TCP uses _________ as error error detection
a. check sum
b. CRC
c. Parity check
d. LRC
13. ________ involves preventing too much data from being injected into the network,
thereby causing switches or links to become overloaded.
Ans: Congestion control
14. A TCP connection are likely to have different ____
Ans: RTT
15. The server which is willing to accept data is in ______ state
Ans: passive open
16. _____ is a mechanism used to increase the congestion window rapidly from a cold start.
Ans: slow start
17. In which method a single bit is added to the packet header to predict congestion .
Ans: DECbit
18. In ____________ mail in the sender is not deleted after download
a.
b.
c.
d.
IMAP
POP3
SMTP
ICMP
19. _________ is one of the FTP transfer parameter command
a. STRU
b. ALLO
c. REST
d. STOR
20. ________ allows a user to connect to a remote host and upload or download the files.
a. TCP
b. UDP
c. FTP
d. SMTP_
21. ______ maintains the domain name system.
a) distributed database system
b) a single server
c) a single computer
d) none of the mentioned
22. _________contains all labels, from the most specific to the most general, that uniquely
define the name of the host.
a. Fully Qualified Domain Name(FQDN)
b. Partially Qualified Domain Name(PQDN)
c. Both FQDN and PQDN
d. None of the above
23. The formal protocol that defines the Mail Transfer Agents( client and server) in the Internet is
called _________
Ans:Simple Mail Transfer Protocol (SMTP).
24. The process of transferring a mail message occurs in the following order of phases :
Ans: connection establishment, mail transfer, and connection termination.
25. The two modes of POP3 protocol are:
26. Ans: the delete mode and the keep mode.
27. _________ the standard mechanism provided by TCP/IP for copying a file from one host to
another.
Ans: FTP
28. 11. The two types of DNS message are:
Ans: query and response
Refer the Figure 1 to answer the questions number from 16 - 24)(12)
29. Identify the time periods when TCP slow start is operating. (2)
0 - 4, 7 – 10
30. Identify the time periods when TCP congestion avoidance is operating (AIMD).(3)
4 - 6, 10 - 14, 15 - 17
31. At the 6th RTT, is the segment loss detected by_______ (1)
32. What is the initial value of ssthreshold, before the first congestion avoidance interval?
(1)
16
33. What is the value of ssthreshold, after the first congestion avoidance interval?(1)
9
34. At the 14th RTT, is the segment loss detected by________ (1)
35. What is the value of ssthreshold, after the second congestion avoidance interval? (1)
6
36. Assuming a packet loss is detected after the 17th RTT by the receipt of a triple duplicate
ACK, what will be the values of the congesion-window size and of ssthreshold? (1)
4,4
37. Assuming a packet loss is detected after the 17th RTT by the receipt of a timeout , what
will be the values of the congesion-window size and of ssthreshold?(1) 4,1
1/31/22, 2:22 PM
Tutorial 1
Tutorial 1
Total points 20/20
The respondent's email (19z350@psgtech.ac.in) was recorded on submission of this form.
If the network bandwidth = 10Mbps, what is the time taken to transmit
one bit?
2/2
10^7 s
0.1 micro sec
0.1 s
10s
Logical addressing is a service provided by ______ layer in OSI reference 1/1
model.
network
datalink
transport
physical
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1/31/22, 2:22 PM
Tutorial 1
The type of network that handles the interconnection of IT devices at the 1/1
surrounding of a single user is called _____________________
local area network
metropolitan area network
personal area network
wide area network
What is the propagation delay if the distance between the two points is 2/2
12,000 km? Assume the propagation speed to be 2.4 x 10^8 m/s in cable.
50s
100s
50ms
100ms
The number of bits that can be transmitted over the network in a certain 1/1
period of time is called __________.
round trip delay
propagation delay
bandwidth
transmission delay
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Tutorial 1
SMTP is a protocol in ______ layer of TCP/IP model.
1/1
network
application
transport
link
The hiding of details behind well-defined interface is called __________
1/1
layering
decoding
abstraction
encapsulation
The process of determining systematically how to forward messages
towards the destination node based on its address is called __________
1/1
Encoding
Multiplexing
Routing
Linking
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Tutorial 1
______ connector is used to connect coaxial cable.
1/1
BNC
RJ45
SC connector
ST connector
For a noiseless channel, the Nyquist bit rate formula defines the
1/1
theoretical maximum bit rate is given by: Bit Rate = 2 x bandwidth x
1og(base 2) L . What does L stands for?
number of signal levels used to represent data.
data bits per signal level
total number of data bits
peak value of the signal levels
The communication type where source node sends a message to all the 1/1
nodes is called _________
anycast
unicast
multicast
broadcast
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Tutorial 1
_____ cable has a metal foil or braided mesh-covering that encases each 1/1
pair of insulated conductors.
unshielded twisted pair
shielded twisted pair
optical
coaxial
_______ is the maximum value or strength of the signal over time
1/1
Frequency
Time
Phase
Amplitude
Consider a point-to-point link 50 km in length. At what bandwidth would 2/2
propagation delay(at a speed of 2x10^8 m/s) equal transmit delay for
100-byte packets?
3.2 kbps
2.5 Mbps
3.2 Mbps
2.5 kbps
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Tutorial 1
Consider a dial-up connection whose bandwidth is 56kbps with RTT of
2/2
87 micro seconds. The maximum number of bits in transit at a particular
time.
3
6
5
4
If there are 5 nodes connected using bus topology then the number of
1/1
links is ___________
2
4
5
6
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1 mark qns:
1. A class of switches that connects Ethernet segments are called as _________
Ans: bridges
2. The protocol which is mainly used to deal with interconnection of different type is called
__________
Ans: IP
3. The path taken by a packet in a network should have the following characteristics:
Ans: loop free, respond to addition of new nodes, respond to failure of existing nodes.
4. If a connection has to be made by allocating dedicated resources it is called as ______
Ans: circuit-switching
5. Which of the following is a type of packet switched network
Ans: datagram, virtual-circuit switched
6. _______________ is used to uniquely identify a connection to a switch.
Ans: virtual circuit identifier (VCI)
7. In this approach, to establish a connection state by virtual circuit switching, the host sends
messages/signal into the network to cause the state to be established.
Ans: switched virtual circuit (SVC)
8. For the following network topology, what can be the content of virtual circuit table if the packet
has to move from host A to host B
Ans: 3,7,2,6
9. If all the information about network topology that is required to switch a packet across the
network is provided by the source host then the type of switching is called
Ans: source routing
10. The minimum size of IPv4 header is _______
Ans: 32
11. ___________ is the largest IP datagram that it can carry in a frame.
Ans: maximum transmission unit (MTU),
12. The default value of TTL in IPv4 header is __________
Ans: 64
13. Header length in IPv4 header specifies the length of the header as ____
Ans: 32 bit word
14. Protocol to convert IP address to link-level address is ______
Ans: Address Resolution Protocol (ARP)
15. In ARP the value of Hardware type field if the link-level technology used is Ethernet and network
protocol used is IPv4 is
Ans: 1
16. The type of communication for an ARP request is _______
Ans: broadcast
17. The protocol used if the host system has to be configured to connect to a network automatically
is called ______
Ans: DHCP
18. DHCP is derived from __________ protocol
Ans: BOOTP
19. The error reporting protocol associated with IP is ____
Ans: Internet Control Message Protocol (ICMP)
20. Debugging tool that uses ICMP is
Ans: ping, traceroute.
2 mark qns(as MCQs):
1. Advantages of having a switch in network:
Ans: many hosts can be connected to a switch, connection can be made between two switches,
network with switches is scalable, hosts connected with switch can transmit at full link speed.
2. Following are the characteristics of a datagram network:
Ans: host can send packet anywhere at any time, each packet is treated independently, link
failure many not be a serious problem, packets from a specific source to specific destination can
take different paths, sender host need not know whether then network will be able to deliver
the packet to the destination, no connection establishment phase
3. Which of the following are the characteristics of virtual circuit switching?
Ans: if a link fails, new connection has to be established, if the switch fails, new connection has
to be established, requires routing algorithm, per packet overhead is reduced when compared
to the datagram model, has connection establishment phase, has to send tear-down
signal/message to disconnect the connection
4. The following are the characteristics of IP protocol
Ans: can build scalable network, can build heterogeneous network, uses logical addressing, uses
datagram approach to forward packets, packets are sent in a connectionless manner, does not
make any attempt to recover from failure, can deliver out-of-order packet, can deliver duplicate
packet.
5. The following are the fields of IP header with the size of the fields in bits :
Ans: Version number – 4 bits, Header length -4 bits, Type of service – 8 bits, length of the
datagram – 16 bits, Time to live -8 bits, protocol – 8 bits, checksum -16 bits, source address – 32
bits, destination address – 32 bits, fragment identifier-16 bits, fragment flags – 3 bits, fragment
offset – 13 bits (any 4 options can be given)
1. Nodes that support users and run application programs.
Ans: Host
2. Byte string that identifies a node is called _______
Ans: Address
3. When an application uses the ___________service, the client and the server (residing in different
end systems) send control packets to each other before sending packets with real data.
Ans: connection-oriented
4. The internet’s connectionless service is ________
Ans: UDP
5. In __________ the resources needed for communication between the end-systems are reserved for
the duration of the session.
Ans: Circuit-Switched Networks
6. The hiding of details behind well-defined interface is called __________
Ans: abstraction
7. Which of the following is a valid IP address:
Ans:
8. The range of System ports/ Well known ports is ____________
Ans: 0 – 1023
9. The number of bits that can be transmitted over the network in a certain period of time is called
__________.
Ans: bandwidth
10. The communication type where source node sends a message to a subset of nodes but not all
nodes is called _________
Ans: multicast
11. If the switch run out of buffer space, some packets are dropped. This operating state is called
_______
Ans: Congested.
12. Repeater belongs to __________ layer in a network model.
Ans: Physical
13. The layer in the network model that handles routing among nodes within a packet-switched
network is ______________
Ans: network
14. The type of network that handles the interconnection of IT devices at the surrounding of a single
user is called _____________________
Ans: personal area network
15. If there are 10 nodes connected using bus topology then the number of links is ___________
Ans: 11
16. What is the propagation delay if the distance between the two points is 12,000 km? Assume the
propagation speed to be 2.4 x 108 m/s in cable.
Ans: 50ms
17. What is the transmission time for a 2.5-kbyte message (an e-mail) if the bandwidth of the network
is 1 Gbps? Assume that the distance between the sender and the receiver is 12,000 km and that
light travels at 2.4 x 108 mls.
Ans: Transmission time = 0.020ms
18. Consider a dial-up connection whose bandwidth is 56kbps with RTT of 87 micro seconds. . The
maximum number of bits in transit at a particular time.
Ans: 5
19. Assume that Source S and Destination D are connected through an intermediate router R. How
many times a packet has to visit the network layer and data link layer during a transmission from S
to D?
Network layer – 4 times, Data link layer – 4 times
Network layer – 4 times, Data link layer – 6 times
Network layer – 2 times, Data link layer – 4 times
Network layer – 3 times, Data link layer – 4 times
20. The OSI layers that is resent only at the end hosts are
Ans: transport,session,presentation,application
PSG COLLEGE OF TECHNOLOGY, COIMBATORE - 641 004
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
BE CSE, SEM V
CONTINUOUS ASSESSMENT TEST 1
Date: 13/09/2021
19Z504 COMPUTER NETWORKS
Time: 75 min.
Maximum Marks: 50
INSTRUCTIONS:
1. Answer ALL questions. Each question carries 10 Marks.
Answer the following:
1. Consider a network that uses one switch. We need to send two packets of size is 10000.
Transmission time for each packet is 500 μs. Two hosts are connected via a packet switch
with 107 bits per second links. Each link has a propagation delay of 20 μs. The switch begins
forwarding a packet 35 μs after it receives the same. If 20000 bits of data are to be
transmitted between the two hosts using a packet size of 10000 bits, what is the time elapsed
between the transmission of the first bit of data and the reception of the last bit of the data.
(10)
2. Discuss about the OSI reference model of computer networks with neat sketch.
(10)
3. Given the data word 1010001101 and the divisor 110101.Show the generation of the
codeword at the sender site and Show the checking of the codeword at the receiver site using
CRC technique.
(10)
6
4. Frames of 1000 bits are sent over a 10 bps duplex link between two hosts. The
propagation time is 25ms. Frames are to be transmitted into this link to maximally pack
them in transit (within the link).What is the minimum number of bits that will be required
to represent the sequence numbers distinctly? (Assume that no time gap needs to be given
between transmissions of two frames).
(i)
If receiver window size is one
(ii)
If receiver window size is equal to sender window size
5. What is meant by Hidden Terminal and Exposed node Problems? How to solve it?
Illustrate with the suitable examples.
(10)
PSG COLLEGE OF TECHNOLOGY, COIMBATORE - 641 004
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
BE CSE, SEM V
CONTINUOUS ASSESSMENT TEST 3
Date: 18/11/2021
19Z504 COMPUTER NETWORKS
Time: 60 min.
Maximum Marks: 35
PART B
Answer the following
(2x10=20 marks)
1. i.Describe the purpose of the sequence number in TCP
(6 marks)
ii. Suppose Host A sends two TCP segments back to back to Host B over a TCP connection.
The first segment has sequence number 80; the second has sequence number 110.
a. Suppose that the first segment is lost but the second segment arrives at B. In the
acknowledgment that Host B send to Host A, what will be the acknowledgment number?
b. How much data is in the first segment?(4 marks)
2. What is DHCP and describe how it works?(10 marks)
PSG COLLEGE OF TECHNOLOGY, COIMBATORE - 641 004
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
BE CSE, SEM V
CONTINUOUS ASSESSMENT TEST 2
Date: 21/10/2021
19Z504 COMPUTER NETWORKS
Time: 60 min.
Maximum Marks: 50
1. A router maintains the following routing table and it can deliver the packets directly to
hosts through interfaces and can forward the packet to the routers Rn (n =2, 3, &4). (10)
With the following destination IP addresses, what does the router do?
(a) 128.96.171.91
(b) 128.96.167.152
(c) 128.96.163.153
(d) 128.96.169.193
(e) 128.96.165.122
2. Consider a message from TCP layer contains 1044 bytes of data without including the header.
It is passed to network layer’s IP protocol for delivery across 3 networks with MTUs 1024
and 500 and 200. Show the values of all the Flag bits and offset field of IP header and the size
of each data packet (without header) when it passes though each network and reach the
destination host. (Assume all IP and TCP headers are 20 bytes).
(10)
3. (i) For the network given in the Figure 1, give the datagram forwarding table (both initial and
final) for each node. The links are labeled with relative costs; your table should forward each
packet via the lowest-cost path to its destination using distance vector routing.
(10)
Figure 1
(ii) Consider the figure 2. Initially both the node A and B know how to reach node C. But
suddenly the link B to C goes down. What will happen in distance routing and also discuss
how to overcome that problem?
(5)
A
1
1
B
C
Figure 2
4. Consider a traditional Class C address space like 192.168.1.0/24and an organization wants to
formsubnets for four departments, with hosts as follows:
A) CSE: 75 hosts
B) EEE: 50 hosts
C) Civil: 25 hosts
D) ECE: 20 hosts
Design the subblocks and show the first and last address of each subblocks (using slash
notation). Find out how many addresses are still available after these allocations
(15)