Ref. No. Ex/PG/SWE/T/115A/175/2013

Department of InforEjlation technologyM.E. Software Engineering '3"Semester Examination 2013

Subject: Network TechnologiesTime: 3 Hours

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~ li.

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Full Marks: 100(Answer must be brief and to the points)

Answer any five questions

a.(8+5+ 3+4)

Explain how the telephone network might modify the way calls are handled to provide thefollowing services:

i. Call waiting: a special sound is heard when the called party is on the line andanother user is trying to reach the called party.

ii. Call anSwer: if the called party is busy or after the phone rings a prescribednumber of times, the network gives the caller the option of leaving a voicemessage.

b. Discuss the similarities between the following nation transportation network and acommunication network.

i. Railroad Networkii. Highway System

c. Protocol Independence is an important issue. Why? Find out where this important issue isignored in the Internet.

Suppos~ shared ~mediulTf'!vi""offers'll) ilasts A ;.~7i"'.1~"c.;:. Av in lountl-robin fashi'On anopportunity to transmit one packet: hosts that have nothing to transmit immediately relinquishM. How does this differ from STDM? How does network utilization of this scheme comparewith STDM?

a.. (4+5+5+6)

Suppose a transmission channel operates at 3 Mbps and has a bit error rate of 10-3. Bit erroroccurs at random and independent of each other. Suppose that the following code is used. Totransmit a I bit, the codeword III is sent; to transmit a 0 bit, the codeword 000 is sent. Thereceiver takes the three received bits and decides which bit was sent by taking the majorityvote of three bits. Find the probability that the receiver makes a decoding error.

b. 1.5 Mbps communication link uses HDLC to transmit information to the moon. What is thesmallest possible frame size that allows continuous transmission? The distance between earthand the 11100nis approximately 375000km, and the speed of signal propagation is 3x IORm/s.

c. The sliding window protocol can be used to implement flow control. We can imagine doingthis by having the receiver delay ACKs, that is, not send the ACK until there is free. bufferspace to hold the next frame. In doing so, each ACK would simultaneously acknowledge thereceipt of the last frame and tell the source that there is now free buffer space available tohold the next frame. Explain why implementing flow control in this way is not a good idea.

d. Compare the operation of Stop-and-Wait ARQ and bidirectional Go-Back-N ARQ with awindow size ot: I. Sketch out a sequence of frame exchanges using these protocols andobserve how the protocols react to the loss of information frame and to the loss ofacknowledgement frame.

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a.. (3+4+3+3+7)

Suppose that a group of workstations is connected to an Ethernet LAN. If the workstationscommunicate only with each other, does it make sense to use TP in the workstations? Shouldthe workstations are TCP directly over Ethemet? How is addressing handled?

b. An application requires the transfer of network layer packets between clients and server onthe same LAN. Explain how reliable connection oriented service can be provided over anEthernet.

c. Modern Ethernet do not use CSMA/CD. Why?

d. Suppose a group of 10 stations is serviced by an Ethemet LAN. How much bandwidth isavailable to each station if .

i. The 10 stations are connected to a 10 Mbps Ethernet Hub.ii. The 10 stations are connected to a 10 Mbps Ethernet switch.

e. Consider a Ikm, I Mbps token bus system in which the token is passed on a broadcast bus.Assume that the token is passed down the logical ring through N active stations in a way thatcauses a minimum amount of propagation overhead. Also, assume that there are total of 10stations, which are distributed evenly on the bus with equal propagation delay between twoneighboring stations. If the average transmission rate from each active station is 100packets/second and the signal propagation speed is 10000km/s, what is the channel utilizationfor packet size 1000 bits?

a.(3+5+ 3+9)

Consider a "fast" circuit switching network in which the first packet in sequence enters thenetwork and triggers the setting up of a connection "on-the-fly" as it traces a path to itsdestination. Discuss the issues in implementing this' approaclfin packet"Switching.

b. A 64-kolobyte message is to be transmitted over two hops in a network. The network limitspackets to a maximum size of 2-kilobytes, and each packet has a 32-byte header. Thetransmission lines in the network are error free and have a speed of 50Mbps. Each hop is 1000kmlong. How long does it take to get the message from the source to the destination?

c. Why connection less service is less efficient to stop congestion setting up, but better to havewhen congestion set up?

d. Consider the following six node network. Assume all links have bit rate R.

I. Suppose the network uses datagram routing. Find the routing table for eachnode, assuming minimum-hop routing.Explain why the above routing tables lead to inefficient use of networkbandwidth.Suggest an approach in which the routing tables in datagram network aremodified to improve efficiency. Give the modified routing table.

II.

111.

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a.. (6+3+3+3+5)

An organization has been assigned the prefix 212.1.1.0/24 and wants to form subnets for fourdepartments, with hosts as follows:

A 75 hostsB 35 hostsC 20 hostsD 18 hosts

i. Give a possible anangement of subnet masks to make this possible.ii. Suggest what the organization might do if department D grows to 32 hosts.

b. ARP only permits address resolution to occur on a single network. Could ARP send a requestto and get a reply from a remote server using an IP datagram?

c. Three subnets have the following network prefixes:57.6.96.0/21,57.6.104.0/21,57.6.112.0/21, and 57.6.120.0/21

If these network prefixes are aggregated into a single route, what willnetwork prefix and the mask?

be the aggregated

d. Why does IPv6 allow fragmentation at the source only?

e. Suppose hosts A and B are on an Ethernet LAN with IP network address 200.0.0/24. It isdesired to attach a host C to the network via a direct connection to B. Explain how to do thiswith subnets; give sample subnet assignments. Assume that an additional network prefix isnot available. What does this do to the size ofthe Ethernet LAN?

a.(4+4+6+6 )

Suppose we need a communication service to transmit real time voice over the Internet. Whatfeatures ofTCP and what features ofUDP are appropriate?

b. What do you mean by delay-bandwidth product? Do you think that delay-bandwidth productmust be considered for designing new protocol?

c. Suppose you are transfening a file of 10MB over a network, which has a capacity of 20 MBand 50 msec one-way delay. The packet size used in network is I KB. The initial slow startthreshold is set to 10MB. What is the effective throughput achievable for TCP?

d. What problem does TCP Reno have with multiple packet losses from a window? Give anexample to illustrate.