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Old May 31st, 2014, 05:57 PM
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Default Re: BITS Pilani, First Semester Computer Networks (BITS C481) Comprehensive previous

As you want to get the BITS Pilani, First Semester Computer Networks (BITS C481) Comprehensive previous years question papers so here is the information of the same for you:

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Expected Time: 90 min PART-A Max Marks: 42
Q.1 Answer the following. [Application Layer/Basic Networks] [4x3=12M]
I) Host A sends a message to host B over a path of Q links. The message contains M
packets of L bits each. Each link transmits at R bps. Assume there is no queuing delay
and propagation delay is also negligible.
a) How long does it take to send the message from A to B, if the network is packet
switched datagram network and a connectionless service is used? Assume each packet
has h bits of header.

b) How long does it takes to send the message over a circuit switched network of R bps
transmission rate. Assume ts setup time and h bits appended to the message as header?
II) Consider a buffer with 100 packets queued; each packet is 1500 bytes in length. The
buffer is for an intermediate node with a 100 Mb/s output link. How long will it take for
all packets to be transmitted (that is, for the buffer to empty out)?
III) Is it possible for an organization’s Web server and mail server to have exactly the
same alias for a hostname? How it is achieved?

IV) How is it possible for the “If Modified Since” cache-validation technique to work for
http request, even if the two machines have vastly different notions of time (i.e., no
clock synchronization)?

Q.2 Answer the following. [Transport Layer] [3x3=9M]
I) Host A sends a TCP segment (Seq=43, ACK=103) with payload of 14 bytes. The host B
successfully received the segment and wants to send a segment with payload of 14
bytes. What will be the value of Seq and ACK field in the reply from host B? Assume that
host A sends the first segment to the host B after connection setup.
II) Consider a pipelined protocol such as Go back N or selective repeat, where
the packet size is denoted by S, the acknowledgement size is A, the Window size is W,
the transmission rate is R (in either direction), and the round trip time is denoted by RTT.
Assuming the network does not introduce errors and is lightly loaded so that there is no
queuing delay, and that an ACK is sent for each packet; calculate the smallest window
size (in terms of S, A, R and RTT) which allows the sender to send data without idling.
Draw the time line diagram to illustrate your answer.
III) In a good multi-path datagram network (i.e. packet will be delivered through
different paths and different path has different transmission rate), what is the main
advantage of the Selective Repeat over simple Go-back-N?

Q.3 Answer the following. [Network Layer] [3x3=9M]
I) Consider destinations connected to a single source (i.e. root of the tree) by a binary
tree of routers as shown in Fig.1. Each time a packet is sent over a single link, it incurs
one unit of cost.

Assuming there are only 48 destinations (as shown in the Fig.1), what is the cost of
sending a broadcast packet using- a) N-way-unicast.
b) Spanning-tree broadcast.

II) What are the IETF (Internet Engineering Task Force) community arguments for using
NAT (Network Address Translation) to overcome from IP addresses shortage? Write any
three of them.
III) Consider a router inside one AS that receives a packet for a network inside another
AS. Briefly explain how the router decides which router to send it to in its own AS so that
it can reach the other AS.
Q.4 Answer the following. [Link Layer] [4x3=12M]
I) A 15 bit data word along with parity bits received by the receiver is as follows:
101010 111111 011100 110100.
Consider the two-dimensional odd parity error detection mechanism to find out which bit
is received in error? If, any. The bits shown in bold with underline are parity bits. Assume
sender divides the data in a group of 5 bits each to calculate the parity bits.
II) What is IP over ATM? What are the advantages and disadvantages of small ATM cell
III) Assume the round-trip propagation delay for Ethernet is 46.4 micro second. This
gives a minimum packet size of 512 bits (464 bits corresponding to propagation
delay+48 bits of jam signal).
a) What will be the minimum packet size if the delay remains constant and the data rate
rises to 100 Mbps?
b) What is the drawback to so large a minimum packet size?
IV) A bit string 0111101111101111110, needs to be transmitted at the data link layer
using HDLC protocol. Is there any modification is required to bit stream to send it across
the link? Justify. If yes, what would be the correct bit stream?
End of Part A

PART-B Max Marks: 38
Q.1 Consider a network path consisting of four 10 Mbps Ethernet LAN segments A, B, C and D
connected by three store and forward switches S1, S2, S3 as shown in Fig.2. Assume
that each LAN segment introduces a propagation latency of 10 micro seconds, but the
switches introduce no queuing delays. [1+2+2=5M]
a) Calculate the path’s one way latency (total packet delay) for sending a 1 KB frame
from host H1 to host H2.
b) Calculate the effective bandwidth (i.e. actual utilization of the bandwidth) for sending
1KB frame across this path.
c) Calculate the effective bandwidth for sending a sequence of 1KB frames if the source
H1 must wait for a 20 Byte ACK of the previous frame before it can send the next packet
to the destination H2.

Q.2 Consider the Fig.2 that shows the interconnection of six LAN segments (LAN A, LAN B,
LAN C, LAN D, LAN E, and LAN F) using five bridges (B1, B2, B3, B4, and B5). The
numbers shown in figure are representing port numbers of bridges. For example B4 have
three ports numbered as 1, 2, 3. Assume that all links are of equal cost. [2+3=5M]
a) How the frame transmission is affected in the network with the loop created by
bridges B1, B3, and B4? Explain.
b) Identify the route-bridge, route ports and designated ports using spanning tree
algorithm. Show the resultant spanning tree.

Q.3 Consider the network topology shown in Fig.4. The numbers on links between the nodes
represent the cost corresponding to these links. [4+3+1=8M]
a) Using the distance vector algorithm, show the distance tables at node E. Assume that
all nodes simultaneously receive distance vectors from their neighbors, compute their
new distance vectors, and inform their neighbors if requires.

b) What would be the minimum change in link cost between the nodes C and D that
creates the routing loop between node B and C? How does RIP protocol solve this looping
c) Assume the IP addresses of the 5 nodes A, B, C, D and E are,
130,132,5,33, 130,132,5,34, 130,132,5,35 and 130,132,5,36. Assume A is the BGP
gateway router of the AS represented by the given network. What is the appropriate
prefix that node A can announced to other network?
Q. 4 Consider the network shown below which has eight hosts H1,…,H8 and seven routers
R1,…,R7 each of which is much faster than any of the links. All links are full-duplex with
bandwidths as shown in the Fig.5. Show which routers can never be congested and which
ones are more vulnerable to congestion. Justify your answer with proper arguments.

Q.5 Consider the plot shown in Fig. 6 of TCP congestion window size as a function of time for
two TCP connections A and B. In this problem we will suppose that both TCP senders are
sending large files. We also assume that the packet loss events are independent in
connection A and B. [2+2+1+3+3=11M]
a) Considering the above values of congestion window for the connections A and B, can
you identify the type of TCP connections (Reno or Tahoe) that have been used? Justify
your answer.
b) What are the values of the Threshold parameter between the 1st and the 14th
transmission rounds for each connection?

c) At the 12th transmission round for connection A, is segment loss detected by a triple
duplicate ACK or by timeout? Justify your answer.
d) Draw the congestion window values of both connections up to the 20th transmission
round, considering that there neither timeout nor duplicate ACK for any of the
connections. (Extend the Fig.6)
e) Assume that the segment size is 1460 bytes and that a total of 87600 bytes have
been successfully transmitted over connection A before the 13th transmission round. At
which transmission round the cumulative amount of the successful transmitted data is
equal to 163520 bytes? Again assume that there is neither timeout nor duplicate ACK
after the 13th transmission round.

Q.6 Consider the networks shown in the Fig.7. There are two user machines m1.a.com and
m2.a.com in the network a.com. Suppose the user at m1.a.com types the URL
www.b.com/myfile.htm into a browser to retrieve a file from www.b.com. Immediately
after (in few minutes), machine m2.a.com makes a request to the same URL that
m1.a.com made. What will be the sequence of DNS and HTTP messages are exchanged
to fulfill the second request made by m2.a.com? [5M]

Assume that Every HTTP request come from a.com is passing through HTTP cache server
and all DNS requests are iterated queries.

For more detailed information I am uploading PDF files which are free to download:

Contact Details:
Birla Institute of Technology and Science
Vidya Vihar,
Rajasthan 333031 ‎
01596 242 192

Map Location:
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Old October 27th, 2015, 02:39 PM
Default Re: BITS Pilani, First Semester Computer Networks (BITS C481) Comprehensive previous

Can you please give here sample paper of BITS Pilani for First Semester Computer Networks (BITS C481) subject Comprehensive Examination?
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Old October 27th, 2015, 02:48 PM
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Join Date: Dec 2011
Default Re: BITS Pilani, First Semester Computer Networks (BITS C481) Comprehensive previous

As you want ia m here giving you sample paper of BITS Pilani for First Semester Computer Networks (BITS C481) subject Comprehensive Examination.

Paper :

Q.1 Answer the following. [Transport Layer and Network Layer] [5x3=15M]

i) An organization is granted the block The administrator wants to
create 32 subnets.
a) What is the subnet mask in x.y.z.t/n notation?
b) What is the range of addresses in first and last subnet?
c) How many addresses are in each subnet?

ii) You are hired to design a reliable byte-stream protocol that uses a sliding window
like TCP. This protocol will run over a 100-Mbps network. The RTT of the network
100 ms, and the maximum segment lifetime is 60 seconds. How many bits would
you include in the Advertised Window field of your protocol header?

iii) Suppose one IPv6 router wants to send a datagram to another IPv6 router, but
the two are connected together via an intervening IPv4 router. How the datagram
will be sent using tunneling?

iv) Draw the multicast tree for the network given in Fig.1 using RPF (Reverse Path
Forwarding) algorithm.

BITS Pilani : Computer Networks (BITS C481) Comprehensive Exam Paper


Birla Institute of Technology and Science
Pilani Campus, Vidya Vihar
Pilani, Rajasthan 333031
Answered By StudyChaCha Member

Last edited by Aakashd; August 12th, 2018 at 09:06 AM.
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