Puzzles and Aptitute Questions - Revathi R, III IT 'B'

Puzzles and Aptitude Questions

 

§  Three friends divided some bullets equally. After all of them shot 4 bullets the total number of bullets remaining is equal to the bullets each had after division. Find the original number divided

 

Answer:

                    Assume that initial there were 3*X bullets. So they got X bullets each after division. All of them shot 4 bullets. So now they have (X - 4) bullets each. But it is given that, after they shot 4 bullets each, total number of bullets remaining is equal to the bullets each had after division i.e. X Therefore, the equation is3 * (X - 4) = X3 * X - 12 = X2 * X = 12X = 6Therefore the total bullets before division is = 3 * X = 18

 

§  In how many different ways can the letters of the word 'LEADING' be arranged in such a way that the vowels always come together?

 

A.360                                      B.480

C.720                                      D.5040

E. None of these

 

Answer:  Option C

 

Explanation:

The word 'LEADING' has 7 different letters.

When the vowels EAI are always together, they can be supposed to form one letter.

Then, we have to arrange the letters LNDG (EAI).

Now, 5 (4 + 1) letters can be arranged in 5! = 120 ways.

The vowels (EAI) can be arranged among themselves in 3! = 6 ways.

Required number of ways = (120 x 6) = 720.

§  A box contains 2 white balls, 3 black balls and 4 red balls. In how many ways can 3 balls be drawn from the box, if at least one black ball is to be included in the draw?

 

A.        32                                            B.        48

C.        64                                            D.        96

E.         None of these

 

Answer:  Option C

Explanation:

We may have(1 black and 2 non-black) or (2 black and 1 non-black) or (3 black).Required number of ways= (3C1 x 6C2) + (3C2 x 6C1) + (3C3)

    = 3 x6 x 5 + 3 x 2 2 x 1 2 x 1x 6 + 1

                = (45 + 18 + 1)

§  A software engineer has the capability of thinking 100 lines of code in five minutes and can type 100 lines of code in 10 minutes. He takes a break for five minutes after every ten minutes. How many lines of codes will he complete typing after an hour?

 

Answer:    250 lines of codes

 

§  There was a robbery happened at a bank and 3 suspects taken into custody. Their statements
    A:  I am innocent
    B:   I am innocent
    C:  B did it.
   In these three, one is lying and find the culprit

Answer:

if A lied
 complement of A (~A) and C contradicts so not possible
if B lied
 no contradiction on three statements A, ~B, C
if C lied
not possible to determine the culprit clearly because ~C only gives B did not done that, but no proof who done that
So the answer is B lied and B is Culprit

 

§  Find the 3 digit no. whose last digit is the square root of the first digit and second digit is the sum of the other two digits. And that number is divisible by 2,3,6,7. What is that number?

Answer :                  462

 

§  Today is Saturday. A person wants to meet a lawyer and as that lawyer is busy he asks him to come three days after the before day of the day after tomorrow? On which day the lawyer asks the person to come?

Answer:

Today is Saturday.  Day after tomorrow will be Monday. Day before day after tomorrow must be Sunday. Then Three days after the day before the day after tomorrow is Wednesday. That is the answer

§  A person travels at a speed of 10 mph from one city to another. However while returning as there was  not much traffic. He  came with a speed of 15mph. what is his average speed? 

Answer:
                   Average Speed = Total distance travelled/Total Time Taken
                   If x is the distance between cities
                   then Avg Speed = 2x/[(x/10)+(x/15)]
                   Then Average Speed is 12 mph

 

§  If every alternative letter starting from B of the English alphabet is written in small letter, rest all are written in capital letters, how the month  " September" be written.

            (1)        SeptEMbEr   (2)        SEpTeMBEr (3)        SeptembeR    

(4)        SepteMber     (5)        None of the above.

Answer:                 (5).

Explanation:

            Since every alternative letter starting from B of the English alphabet is written in small letter, the letters written in small letter are b, d, f... In the first two answers the letter E is written in both small & capital letters, so they are not the correct answers. But in third and fourth answers the letter is written in small letter instead capital letter, so they are not the answers.

§  A student divided a number by 2/3 when he required to multiply by 3/2. Calculate the percentage of error in his result.

     Answer:     0 %

     Explanation:   Since 3x / 2  = x / (2 / 3)

 

SECURING WIRELESS AD-HOC NETWORKS AGAINST DATA FLOODING ATTACKS - Dharani D, Geetha A, III IT A

SECURING WIRELESS AD-HOC NETWORKS AGAINST DATA FLOODING ATTACKS

ABSTRACT

 

MANET is an emerging research area with practical applications. However MANET is particularly vulnerable due to its fundamental characteristics such as open medium, dynamic topology, distributed co-operation. One of the main challenges is to provide a path with secure robustness in wireless ad hoc networks. In this article we analyze in detail one type of attack-data flooding that can be easily employed against AODV [Ad-hoc On Demand Distance Vector Routing] in MANET. We propose a novel mechanism to secure AODV protocol from data flooding attack.

 

Keywords - MANET, AODV, dynamic topology.

 

 

 

1. INTRODUCTION

 

Mobile Ad-hoc Network (MANET) is a dynamic wireless network that can be formed without any pre-existing infrastructure. Instead each node participates in routing by forwarding data for other nodes and the determination of which node forwards the data is made dynamically based on the network connectivity. This means that a formed network can be de-formed on-the-fly without the need for any system administration. The term "ad-hoc" tends to imply "can take different forms" and "can be mobile, standalone, or networked". Ad-hoc nodes or devices should be able to detect the presence of other such devices and to perform the necessary handshaking to allow communications and sharing of information and services. Routing in ad-hoc networks has been a challenging task ever since wireless networks came into existence. The major reason for this is the constant change in network topology because of high degree in node mobility. In order to establish routes between nodes, which are farther than single hop specially configured routing protocol are engaged. The unique feature of these protocols is their ability to trace routes in spite of a dynamic topology. A number of protocols have been developed for accomplish this task. Ad-hoc On-demand Distance Vector (AODV) is one of the widely used routing protocol that is based on distance vector routing, but the updates are shared not on a periodic basis but on as per requirement basis.

 

 

 

       The remainder of this paper is organized as follows: Section 2 describe an overview of AODV protocol. In Section 3 introduction to Data Flooding attack is given, Section 4 presents related work on MANET security. In Section 5 describes proposed work and Section 6 describes the result analysis and Section 7 describes the conclusion.

 

 

2. AODV OVERVIEW

 

2.1 ROUTING PROTOCOLS IN MANET

 

Routing is an activity or function that connects a call from origin to destination in telecommunication networks and also plays an important role in architecture, design, and operation of networks. MANET routing protocols are classified as

 

i)    TABLE DRIVEN ROUTING PROTOCOLS

 

A proactive routing protocol is also called "table driven" routing protocol. Using a proactive routing protocol, nodes in a mobile Ad Hoc network continuously evaluates routes to all reachable nodes and attempt to maintain consistent, up-to-date routing information. Therefore, a source node can get a routing path immediately if it needs one.

 

Here all nodes need to maintain a consistent view of the network topology. When a network topology change occurs, respective updates must be propagated through the network to notify the change. Some of the table driven routing protocol are Destination Sequence Distance Vector (DSDV), Optimized Link State Routing (OLSR).

 

ii)   REACTIVE ROUTING PROTOCOLS

 

Reactive routing protocols for mobile Ad hoc networks are also called "on-demand" routing protocol. On demand protocols create routes only when desired by source nodes. When a node requires a route to destination, it initiates route discovery process within the network. This process is completed once route is found. Some of the reactive protocols are Dynamic

Source Routing (DSR), AODV.

2.2 WORKING OF AODV PROTOCOL

 

AODV is an on demand protocol as it finds the routes only when required by the source node for transmitting the data. AODV has two phases, the route construction phase and route maintenance phase. In the route construction phase a route must be created from source node to destination node. While in the maintenance is to rebuild a route between source and destination since the previous found route may be broken due to the nodes movement.

 

i)    Construction Phase

 

In the construction phase, when a source node needs to send packets to destination node and if there is no valid route between the source node and destination node, the source node initiates a path discovery process to locate the destination node as shown in Figure 1. The source node will broadcast a route request (RREQ) packet to explore a route to the destination. The source node employs destination sequence number to identify the most recent path. A route request carries source identifier (srcID), the source sequence number (srcseqnum), the destination sequence number (destseqnum), the broadcast identifier (broadcast Id) and time to live (TTL).Destination sequence number are used to identify the most recent path and the freshness of the route is also accepted by the source. A node updates its path information only if the destination sequence number of the current packet received is greater than the last destination sequence number stored at the node.

 

ii)   Route Discovery

 

In the route discovery process, each intermediate node that receives the (RREQ) packet will re-broadcast the packet to its neighbors. The duplicate copies are discarded, if a route request is received multiple times which is indicated by (broadcast ID-source ID pair).Once the RREQ reaches the destination or the intermediate node with fresh route to destination is located, the destination /intermediate node will send a route reply (RREP) packet back to source along reverse route path. Every intermediate node while forwarding a route request enters the previous node address and broadcast ID. A timer is used to delete this entry in case a route reply is not receiving before time expires. This helps in storing an active path at the intermediate node. When a node receives route reply packet information about the previous node from which the packet was received is also stored in order to forward the data packet to the next hop towards the destination.

 

iii)  Route Maintenance

 

If the route between source and destination may be broken since the nodes along the route will move from time to time. If an intermediate node along the route moves, its upstream neighbor will observe the move and propagate a Route Error (RERR) packet to its upstream neighbors and this process continues until source node is reached.

3. FLOODING ATTACK

 

Flooding attack, in which the attacker exhausts the network resources, such as bandwidth and to consume a node's resources, such as computational and battery power or to disrupt the routing operation to cause severe degradation in network performance. For example, in AODV protocol, a malicious node can send a large number of RREQs in a short period to a destination node that does not exist in the network. Because no one will reply to the RREQs, these RREQs will flood the whole network. As a result, all of the node battery power and network bandwidth will be consumed and could lead to denial-of-service will be dropped without forwarding.

 

i)    Data flooding attack

 

Data Flooding Attack in AODV protocol works as follows. At first, the attack node builds up paths to all nodes in the network. Then, the attacker sends large volumes of useless Data packets to all nodes along these paths so that the data packets are forwarded at higher rate.

The mass useless DATA packets will exhaust the communication bandwidth in the network and the destination node will be busy for receiving the excessive useless data packets from the attack node and therefore cannot work normally.

 

 

4. RELATED WORK

 

Most of the previous works on security attacks and its countermeasures in reactive routing protocol such as AODV are specified.

M. Al-Shurman et al. proposed black hole attack that malicious node sends fake routing information, claiming that it has an optimum route and causes other good nodes to route the data packets through the malicious one

 

 

D.Raffo et al. proposed Link Spoofing Attack, in which a malicious node may advertise fake links with non-neighbours to disrupt the routing operations.

 

C.Sreedhar et al. proposed that Symmetric Cryptographic Techniques are used to avoid attacks on routing protocols.

 

 

 

5. PROPOSED WORK

 

In wireless ad hoc networks to conduct the data flooding attack attacker first sets up a path to the victim node because an attack can be performed after constructing the path. Then, the attacker forwards tremendous useless data packets along the path so that the victim node cannot process packets in normal fashion. So finally resources of the victim node are exhausted. In order to measure the effect of data flooding attack in wireless ad hoc networks we are going for Period Based Defense Mechanism. The PDM scheme checks data packet floods at the end of each period in order to enhance the throughput of burst traffic.

 

To prevent malicious data packet flooding attacks with enhancing the throughput of burst traffics, PDM checks data packet floods at the end of each period. It also guarantees the Quality of Service (QoS) of burst traffics. We denote v(nSpnDp) as the variance of the number of received data packets for the source node (nSp) to the destination node (nDp) during T(i-1)-T(i) where i is between 2 and ∞ as shown in Figure 4. The node initiates the period T (i) and h(nSp-nDp) according to its data type.  h (nSp-nDp) is the variance coordinator for data packet floods from nSp to nDp to guarantee QoS. ave (all) is the average number of received all data packets during T(i-2)-T(i-1). Then, the variance limit of data packet floods from nSp to nDp, vlimit (nSp − nDp) = ave(all) + h(nSp − nDp ).

If the end of the period T(i), the node ni compares the variance of each received data packets according to its nSp and nDp pairs (v(nSp-nDp)) with its variance limit vlimit(nSp-nDp). If v(nSp-nDp) is greater than vlimit(nSp-nDp), it checks whether data packets for nSp-nDp (D(nSp-nDp)) are in the blacklist or not. If D(nSp-nDp) is in the blacklist, it is not transmitted until the next period (T(i+1)). If it is not in the blacklist, its priority is determined by the inversion of the number of received data packets. Then, it is processed according to its priority, and the node updates the blacklist by the greatest number of received data packets in the period.

 

Recently many users like to download and share the multimedia data, so we are extending our work to multimedia data transmission. For multimedia transmission we are going to give priorities to multimedia packets and these packets are transmitted faster than the normal packets. So that end to end delay for multimedia packets will get reduced and delivered faster than the normal packets.

 

 

6. RESULT ANALYSIS

 

To validate our analysis, we have to implement Period Based Defense Mechanism (PDM) in multimedia transmission in a simulator and by performing a serious of simulation based experiments to test its effectiveness.

 

Simulation parameters

Simulation time          15 M

Number of nodes       20

Terrain dimensions      (800,800)

Node placement         Uniform

Routing Protocol         AODV

To investigate how much QOS is guaranteed, we have implemented flooding attack by increasing the no. of data packets per second from 20 packets per second to 400 packets per second by assuming that we have 5 attackers. When the no. of packets per second is high, AODV cannot process the packets because of the resource exhaustion.

To compare the affect of the no. of attackers to the throughput, each node including attackers sends 20 packets per second.

 

Hence, the throughput of the PDM scheme is higher than AODV so that it can defend against malicious data packet flooding attacks.

7. CONCLUSION

 

The existing security schemes for wire networks cannot be applied directly to the MANET, which makes MANET much more vulnerable to security attacks. In this paper we have analyzed the routing attacks and countermeasures in MANET. Here we have shown that the data flooding attack paralyzes a victim node by consuming its resources. Hence, the throughput of the victim node is significantly reduced. Hence the Period-based Defense Mechanism (PDM) scheme is used in multimedia data transmission, to efficiently prevent the data flooding attack, as a result of which many data packets are forwarded at a high rate for the whole duration. Hence it enhances the throughput of the burst traffic.