Turbomachinery Institute of Technology & Science - CSE

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Year: III- II Branch: CSE Subject: Computer Networks Name of the Faculty:T. Swapna

Unit I: Introduction: OSI, TCP/IP and other networks models, Examples of Networks: Novell Networks,

Arpanet, Internet, Network Topologies WAN, LAN, MAN.


. (a) Give a detailed description of the Novell Netware IPX packet?
(b) Compare connection less and connection oriented services with suitable examples?
[8+8] (Feb-2008)(Set-1)

(a) Discuss the basic functions performed by different layers of ISO-OSI reference
(b) List two advantages and two disadvantages of having international standards
for network protocols. [10+6] (Set-1)(Nov-2009)
(a) How does Internet differs from WAN?
(b) Give an example where we require
i. Simplex communication
ii. Half duplex communication
iii. Full duplex communication.
(c) What are the two reasons for using layered protocols? [6+6+4] (Set-1)(Nov-2009)
(a) What are the various applications of computer networks?
(b) What are the advantages of multipoint connection over a point-to-point
connection? What are some of the factors that determine whether a communica-
tion system is a LAN, MAN or WAN? [8+8] (Set-3)(Nov-2009)
. (a) What are the advantages of having layered architecture? Mention the layers of
ISO-OSI reference model?
(b) What is Internet? Mention some of the applications of Internet?(Set-3)(Feb 2008)
. (a) How would you utilize an existing telephone network for Computer-to-Computer
data communications?
(b) “Bad Timing” is also a problem for OSI reference model. Discuss. [8+8]
(Set 4)(Feb 2008)
(a) List two advantages and two disadvantages of having international standards for
network, Protocols?
(b) Write short notes on interfaces and services of ISO layers. [8+8](Set-1)(Aug -2008
(a) Explain in detail ISO-OSI reference model.
(b) Write short notes on interface, service and protocol. [8+8]
(Set-2)(Aug-2008)(Set 4)(Aug 2008)
(a) Write any four reasons for using layered protocols.
(b) Compare and contrast OSI and TCP/IP models. [8+8] ](Set-3)(Aug-2008)


Write any four reasons for using layered protocols.

List two ways in which the OSI reference model and the TCP/IP reference
model are the same and list in which they di

er. (Set-4)(Aug-2008)

Which is the principle di

erence between CO communication and CL commu-nication. [6+4+6]


Physical Layer: Transmission media copper, twisted pair wireless, switching and encoding

asynchronous communications; Narrow band, broad band ISDN and ATM.
. (a) What are the reasons for choosing cell switching in ATM?
(b) Discuss about the ISDN architecture in detail? [6+10](Feb-2008)(Set-1)
(a) Explain about ISDN architecture?
(b) Differentiate between optical fiber and coax? [10+6](Set-2)(Nov-2009)
(a) If a binary signal is sent over a 3KHz channel whose signal to noise ratio is
20dB. what is the maximum achievable data rate?
(b) Which switching method allows real-time data transfer? Mention the advan-
tages of packet switching? (set-3)(Feb -2008)
(a) Television channels are 6MHz wide. How many bits/sec can be sent if four
level digital signals are used? Assume a noiseless channel
(b) How does a virtual circuit differ from a physical circuit? What advantages
would a virtual circuit provide? [8+8](Set-3)(Feb 2008)
. (a) The following data fragment occurs in the middle of a data stream for which
the character-stuffing algorithm described in the text is used: DLE, STX, A,
DLE, B, DLE, ETX. What is the output after stuffing?
(b) When bit stuffing is used, is it possible for the loss, insertion, or modification
of a single bit to cause an error not detected by the checksum? If not, why
not? If so, how? Does the checksum length play a role here?
(c) Data link protocols almost always put the CRC in a trailer, rather than in a
header. Why? [6+6+4(set-1)( aug 2008)(set-2 aug 2008)
(a) Compare and contrast SLIP and PPP.
(b) Draw and explain HDLC frame format. [8+8] (Set-3)(Aug 2008)
(a) Briefly, explain about the DLL design issues.
(b) If the bit string 0111101111101111110 is bit stuffed. What is the output of
the string? [8+8](Set-4 aug 2008)


Data link layer : Design issues, framing, error detection and correction, CRC, Elementary

Protocol-stop and wait, Sliding Window, Slip, Data link layer in HDLC, Internet, ATM.

(a) Discuss the basic functions of data link layer in brief?
(b) What is pipelining? Discuss the two approaches of dealing with errors in the
presences of pipelining? [8+8] (Set-1)(Feb-2008)
(a) Discuss the error control technique which is commonly used in data network. What
value of N is used in go-back-N ARQ technique used in ARPANET and why?
(b) Imagine that you are writing the data link software for a line used to send
Data to you, but not from you. The other end uses HDLC, with a 3-bit
sequence number and a window size of seven frames. You would like to bu_er
as many out of sequence frames as possible to enhance e_ciency, but you are
not allowed to modify the software on the sending side. Is it possible to have
a receiver window greater than one, and still guarantee that the protocol will
never fail? If so, what is the largest window that can be safely used?
(Set-2 Nov 2009)(Set-2 Feb 2008)
3. (
a) How POP works? What are the advantages of IMAP over POP?
(b) What is the role played by message transfer agent? Explain.
)(set-2 feb 2008)
. (a) What is the check summed frame transmitted if the message is 1101011011 and the generator

polynomial is x4 + x + 1 using CRC.
(b) Give the detailed description of HDLC frame format? [8+8]? (Set-3 Feb 2008)
(a) Explain about the various services that the data link layer offers to the upper layers?
(b) Compute the fraction of the bandwidth that is wasted on overhead (headers
and retransmissions) for sliding window protocol using selective repeat on a
heavily loaded 50-kbps satellite channel with data frames consisting of 40
headre and 3960 data bits. ACK frames never occur. NAK frames are 40 bits.
The error rate for data frames is 1 percent, and the error rate for NAK frames
is negligible. The sequence numbers are 8 bits.(set 4 feb 2008)
(a) What is collision free protocols? Explain Binary count down protocol.
(b) Explain in detail, Adaptive free walk protocol. [8+8] (Set-1 Aug 2008)
(a) Explain the operation of source Routing Bridges.
(b) Compare and contrast Transparent and Source routing bridges. [8+8]
(Set-2 Aug 2008)(Set 3 Aug 2008)
(a) What is meant by contention systems.
(b) Explain CSMA/CD protocol.
(c) Explain any one Collision free protocol. [4+6+6](Set-4 Aug 2008)
(a) Explain one -bit sliding window protocol. Give the advantages and disadvantages
(b) Discuss the services provided by the data link layer to the network layer?
of one-bit sliding window protocol?[8+8](Set-1 NOV -2008)


What is SLIP? What are the disadvantages of it?

With an example, explain the importance of sequence numbers for Acknowl-
edgements. [8+8](set-3 Apr-2008)


Medium Access sub layer : ALOHA, MAC addresses, Carrier sense multiple access. IEEE

802.X Standard Ethernet, wireless LANS. Bridges
. What is a token? Discuss the protocol of token ring LAN in general. Discuss with
example how priority is implemented in a token ring LAN? [16]
(Feb 2008(set-1) (set-2))
(a) Consider the delay of pure ALOHA versus slotted ALOHA at low load. Which one
is less? Explain your answer
(b) Consider building a CSMA/CD network in at 1 Gbps over a 1-km cable with
No repeaters. The signal speed in the cable is 200,000 km/sec. What is the
Minimum frame size? [8+8](Set-1) Nov (2009)
Write short notes on:
(a) Ethernet
(b) Wireless LAN
(c) Source routing bridge
(d) Remote bridges. [4_4=16](Set-2)(Nov-2009)
(a) What is pure ALOHA and slotted ALOHA? Mention the advantages of slotted
ALOHA? (Set-3) (NOV -2009)
(a) What is the need for wireless communication? Discuss about various portions of
spectrum used for transmitting information?
(b) What is done if the cells arriving at two or more input lines at a ATM switch
want to go to the same output port in the same cycle? [8+8](Set-2)(Feb 2008)
. (a) What is pure ALOHA and slotted ALOHA? Mention the advantages of slotted
(b) A seven-story office building has 15 adjacent offices per floor. Each office
contains a wall socket for a terminal in the front wall, so the sockets from a
rectangular grid in the vertical plane, with a separation of 4 m between sockets,
both horizontally and vertically. Assuming that it is feasible to run a straight
cable between any pair of sockets, horizontally, vertically, or diagonally, how

many meters of cable are needed to connect all sockets using
i. a star configuration with a single router in middle?
ii. an 802.3 LAN?
iii. a ring network (without a wire center )? [6+10]? (Set-3 feb 2008)
. (a) What is the prime difference between a token bus and a token ring?
(b) A large population of ALOHA users manages to generate 50 requests/sec,
including both originals and retransmissions. Time is slotted in the units of
40 msec.
i. What is the chance of success on the first attempt?
ii. What is the probability of exactly k collisions and then a success?
iii. What is the expected number of transmission attempts needed? [4+12]
(Set-4 Feb 2008)
What is congestion? How does it differ from flow control? Discuss about the general principles of

congestion? Briefly discuss about policies that affect congestion. [16]
(Set-1 aug 2008)
(a) What is Broadcasting? With an example, explain about Reverse path
(b) With an example, explain multicast Routing Algorithm. [8+8](Set-2 aug 2008)
(a) With an example, explain Hierarchical Routing Algorithm.
(b) With an example, explain multicast Routing Algorithm. [8+8] (Set-3 aug 2008)
. (a) Write short notes on:
i. Choke packet
ii. Load shedding
iii. Jitter control.
(b) With an example, explain any one adaptive routing algorithm. [8+8]
(Set 4 aug-2008)
(a) Discuss about MAC addresses?
(b) Explain about a bit-map collision free protocol? [8+8](Set 1 Nov 2008)


What is time domain reflectometry?

Write about 802.3 cabling.

Draw and Explain 802.3frame format. [8+8] (Set-2 Apr -2008)


A 4-Mbps token ring has a token-holding timer value of 10m sec.

What is the
longest frame that can be sent on this ring?

(b) In a token ring the sender removes the frame.

What modifications to the

system would be needed
to have the receiver remove the frame instead, and

what would the consequences be?




Network Layer: Virtual circuit and Datagram subnets-Routing algorithm shortest path routing,

Flooding, Hierarchical routing, Broad cast, Multi cast, distance vector routing.

(a) Network layer can provide either connection oriented service or connection less
service. Which one you prefer. Justify your answer
(b) Define Virtual circuit and Datagram. Compare Virtual circuit subnet with
Datagram Subnet. .(set-1)(feb-2008)
(c) Is Virtual circuit same as Physical connection. Comment. [5+8+3](Set 4 Feb 2008)
. (a) Explain the working of Distance vector routing algorithm with the help of an
(b) What is Count to Infnity problem? Suggest solution for it. [10+6](set1)(Nov-2009)
. (a) What is Multicasting? How is it diferent from broadcasting? How do you
construct a multicast tree? Explain with an example.
(b) What are the applications of multicasting. [10+6](set2)(nov2009)
(a) Any V.C. subnet delivers packets in order, but why Datagram subnet fails to deliver
packets in order.
(b) For request-reply type of service which one is preferred connection oriented
Service/connection less service. Why?
(c) Among VC Subnet and datagram subnet, which one maintains state informa-
tion and why? [6+5+5](set-30(nov-2009)
(a) The major problem with Distance vector algorithm is count to infinity. How
exchange of complete path from router to Destination instead of delay, helps
in solving count to infinity problem.
(b) What are the advantages of adaptive routing approach over non adaptive
routing. [10+6](feb 2008)(Set-2)
(a) Consider an organization which has several branches in different cities of India.
How hierarchical routing can be used for routing in such an organization.
(b) Explain how complexity of network layer and transport layer varies with type
of service provided. [10+6](Set-3 feb2008)
(a) Briefly explain the concepts of Flow Control and Buffering.
(b) Imagine that a two-way handshake rather than a three-way handshake were
used to set up connections. In other words, the third message was not required.
Are deadlocks now possible? Give an example or show that none exist. [8+8]
(Set-1 Aug-2008)(set2, set3 Aug 2008)(Set 4 Aug 2008)


Draw and explain in detail Internet Protocol Header (IPV4).

Briefly discuss about IP address classes and special IP addresses.[8+8](set-2 Apr-2008)
Dynamic routing – Broadcast routing. Rotary for mobility. Congestion, Control Algorithms –

General Principles – of Congestion prevension policies. Internet working: The Network layer in the internet

and in the ATM Networks
(a) What is the role played by threshold value in congestion control?
(b) Assume network with links having abundant bandwidth. What are the pros
and cons of using exponential increase and linear increase of congestion win-
dow? What happens if bandwidth is limited? (set-3 nov-2009)
(a) How connections are setup and released in ATM?
(b) What is the Format of routing table in ATM? How it helps in routing cells?
(a) How congestion is controlled in V.C. subnets?
(b) What is Choke packet? How use of choke packets helps in congestion control?
[8+8](feb 2008)(Set-2)
Explain routing in mobile hosts. [16](Set 3 Feb2008)(Set-4 Feb 2008)
(a) Briefly discuss ICMP.
(b) Explain Address resolution protocol. [8+8]9set-1 aug 2008)
(a) Briefly discuss about connection less Internetworking.
(b) Explain firewalls, packet filter and a proxy in detail. [8+8],
. (a) Briefly discuss about the ways network can differ.
(b) Briefly discuss about IP address classes and special IP addresses. [8+8]
(Set-3 Aug - 2008)
. (a) What is internet work routing? Explain interior gateway and exterior gateway
(b) What is three bears problem? Write short notes on CIDR. [8+8](Set 4 Aug 2008)


A computer on a 6-Mbps network is regulated by a token bucket.

The token

bucket is filled at a rate of


It is initially filled to capacity with 8


How long can the computer transmit at the full 6



Briefly discuss about congestion control in VC subnets. [8+8](set-2 Apr-2008)

Transport Layer: Transport Services, Connection management, TCP and UDP protocols; ATM

AAL Layer Protocol.
What are the services provided by Network layer to Transport layer. Explain.
[16](Set-1)(feb 2008)
. (a) Network layer can provide both connection oriented service and connection
less service. Similar is the case with Transport layer, then why two di_erent
layers are required.
(b) What are the Transport layers Quality of Service parameters?
(a) What are the header fields in TCP segment header that are related to only
data transfer? Explain?
(b) What are the header fields in TCP segment header that are required for con-
nection establishment and release? Explain. [8+8](set20(nov 2009)
(a) In TCP Why three-way handshake is required for connection establishment
and release.
(b) Why TCP is not suitable for request-reply type of transfers?
(c) As application developer under what circumstances you use TCP and under
what circumstances you use UDP? [6+5+5](set-4)(Nov 2009)
(a) Why Pseudo header is used in computing TCP Checksum?
(b) Explain how TCP controls congestion? ] (set-2)(feb 2008)(set-4 feb 2008)
. (a) What are the similarities and differences between Data Link layer and
Transport layer?
(b) Explain addressing at Transport layer? [6+10](Set-3 feb2008)
(a) Draw and explain in detail the TCP Header.
(b) Briefly discuss TCP connection Management. [8+8](Set-1 aug-2008)
. (a) Suppose that the TCP congestion window is set to 18K bytes and a timeout
occurs. How bit will the window be if the next four transmission bursts are
all successful? Assume that the maximum segment size is 1 KB.
(b) If the TCP round-trip time, RTT, is currently 30 msec and the following
acknowledgements come in after 26,32, and 24msec, respectively. What is the
new RTT estimate? Use α = 0.9.
(c) Datagram fragmentation and reassembly are handled by IP and are invisible
to TCP. Does this mean that TCP does not have to worry about data arriving
in the wrong order? [6+6+4](set-3 Aug 2008)


Briefly discuss about Transport Layer quality of service parameters.

Briefly explain the concept of Addressing in TL. [8+8](set-2 Apr-2008)


Draw and explain the structure of the ATM Adaptation layer.

Draw and explain the AAL1 cell format, headers and trailers. [8+8]( set-2 Apr-2008)


Suppose that the TCP congestion window is set to 18K bytes and a timeout


How bit will

the window be if the next four transmission bursts are

all successful?

Assume that the maximum
segment size is 1 KB.

(b) If the TCP round-trip time, RTT, is currently 30 msec and the following

acknowledgements come in

after 26,32, and 24msec, respectively.

What is the

new RTT estimate?

= 0.9.

Datagram fragmentation and reassembly are handled by IP and are invisible

to TCP. Does this

mean that TCP does not have to worry about data arriving

in the wrong order?

Application Layer – Network Security, Domain name system, SNMP, Electronic Mail; the World

WEB, Multi Media
Explain in detail SNMP? [16](Set1 Nov 2009)
Explain the architecture and services of e mail system. [16](Set2 Nov 2009)
. (a) What are the advantages of using e mail gateways?
(b) How SMTP protocol works? [8+8](set 3 nov 2009)
Explain how privacy is achieved in e-mail system? [16](Set-3 Feb 2008)
(a) What is Domain? Explain the Internet domain space in the context of DNS.
(b) What is resource record? What is its format?
(c) What are the record types of DNS resource record? [6+5+5](Set-4 Feb 2008)
(a) PGP does not support canonicalization as does PEM. Why not?
(b) Assuming that everyone on the Internet used PGP, could a PGP message be
sent to an arbitrary Internet address and be decoded correctly by all concerned?
Discuss your answer. [8+8](Set-1 Aug 2008)
. (a) What is the difference between message confidentiality and message integrity?
Can you have one without the other? Justify your answer. (Set-1 Aug 2008)
(a) Explain in detail methods of DES chaining.
(b) Briefly discuss about IDEA. [8+8](Set-3 Aug 2008)


Briefly explain Needham-Schroeder authentication protocol.

Explain the operation of Kerberos
. [8+8](set-2 apr-2008)


What is “Quantization noise”?

Briefly discuss about MIDI.

Explain any two compression techniques. [8+8](Set-3 Aug-2008)


What is SMTP? Briefly discuss about Email gateways.

Write short notes on pretty good privacy. [8+8]](Set-3 Aug-2008)