Mobile Ad Hoc NetworkMobile Ad Hoc NetworkMobile Ad Hoc Network Mobile Ad Hoc Network Security (MANET)Security (MANET)

Preethi VishwanathPreethi VishwanathSan Jose State UniversitySan Jose State UniversitySan Jose State UniversitySan Jose State University

Computer ScienceComputer Science

DefinitionDefinitionA " bil d h t k" (MANET) i t t f bil t ( d i t d h t )A " bil d h t k" (MANET) i t t f bil t ( d i t d h t )A "mobile ad hoc network" (MANET) is an autonomous system of mobile routers (and associated hosts) A "mobile ad hoc network" (MANET) is an autonomous system of mobile routers (and associated hosts) connected by wireless links connected by wireless links ----the union of which form an arbitrary graph. the union of which form an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably.topology may change rapidly and unpredictably.Such a network may operate in a standalone fashion, or may be connected to the larger Internet. Such a network may operate in a standalone fashion, or may be connected to the larger Internet. S d i t f i d t i d i ti t d t i ll fS d i t f i d t i d i ti t d t i ll fSensor nodes consist of sensing, data processing, and communication components and typically form Sensor nodes consist of sensing, data processing, and communication components and typically form ad hoc networksad hoc networks..Due to a lack of infrastructure support, each node acts as a router, forwarding data packets for other Due to a lack of infrastructure support, each node acts as a router, forwarding data packets for other nodes.nodes.

Can be classified into twoCan be classified into twoServer: Contain the complete DBMS and bear primary responsibility for data broadcast and satisfying Server: Contain the complete DBMS and bear primary responsibility for data broadcast and satisfying client queries.client queries.Clients: Have sufficient resources to cache portions of the database as well as storing some DBMS Clients: Have sufficient resources to cache portions of the database as well as storing some DBMS

d i d ld i d lquery and processing modules.query and processing modules.

Practical Use : Whenever a temporary network with no infra structure needed.Practical Use : Whenever a temporary network with no infra structure needed.

Rescue situations: Rescue situations: Rescue workers engaged in disaster relief investigate the extent of the damage Rescue workers engaged in disaster relief investigate the extent of the damage g g g gg g g garound them and collaboratively work by sharing the information on their locations and findings.around them and collaboratively work by sharing the information on their locations and findings.

Excavations: Excavations: Members of a research project team engaged in an archeological excavation collect Members of a research project team engaged in an archeological excavation collect various phenomenal data from sensors and share the obtained data with other members to streamline various phenomenal data from sensors and share the obtained data with other members to streamline work.work.

Criteria Criteria –– node to be part of a node to be part of a networknetwork

To be connected to a network, a node should To be connected to a network, a node should ,,must be within the area of influence of at least must be within the area of influence of at least one node on the network.one node on the network.A d i h i i h iA d i h i i h iA node with no remaining power, or one that is A node with no remaining power, or one that is off, is not currently a part of the network.off, is not currently a part of the network.Even if the source and the destination nodes areEven if the source and the destination nodes areEven if the source and the destination nodes are Even if the source and the destination nodes are not within each other’s communication range, not within each other’s communication range, data packets are forwarded to the destination by data packets are forwarded to the destination by relaying transmission through other nodes that relaying transmission through other nodes that exist between the two nodes.exist between the two nodes.

Large Scale On Demand ModelLarge Scale On Demand Model( )( )RRxxW (request Time Waits)W (request Time Waits)

At each broadcast tick, the server chooses an item to broadcast based on At each broadcast tick, the server chooses an item to broadcast based on the number of request and the amount of time the original result has beenthe number of request and the amount of time the original result has beenthe number of request and the amount of time the original result has been the number of request and the amount of time the original result has been waiting.waiting.The overhead for large databases is significant in both time and space.The overhead for large databases is significant in both time and space.ImprovementsImprovementsA h 1 ( G t Al)A h 1 ( G t Al)Approach 1 ( Guo, et. Al)Approach 1 ( Guo, et. Al)

–– Server maintains a list of popular or less popular items.Server maintains a list of popular or less popular items.–– The popular items are continuously broadcast.The popular items are continuously broadcast.–– If a less popular item is needed, a client may request it. If a less popular item is needed, a client may request it.

Thi i t t th b d t hi h ti ith th d t b d t ftThi i t t th b d t hi h ti ith th d t b d t ft–– This interrupts the broadcast, which continues with the data broadcast after This interrupts the broadcast, which continues with the data broadcast after serving the request. serving the request.

–– The server never stops broadcasting, consuming power.The server never stops broadcasting, consuming power.Approach 2 ( Yajima et. Al and Grassi)Approach 2 ( Yajima et. Al and Grassi)

I d t b i b th i ti d f th b d tI d t b i b th i ti d f th b d t–– Improve database service by the organization and use of the broadcast.Improve database service by the organization and use of the broadcast.–– Highly correlated items are found together in the broadcast, minimizing the Highly correlated items are found together in the broadcast, minimizing the

number of times a client must access the broadcast.number of times a client must access the broadcast.–– Uses prefetching related items into the client cache so that they will be available Uses prefetching related items into the client cache so that they will be available

locally if needed.locally if needed.locally if needed. locally if needed. –– While prefetching may shorten the time a client needs to access a data item, While prefetching may shorten the time a client needs to access a data item,

prefetching wastes power and space through accessing and storing broadcast prefetching wastes power and space through accessing and storing broadcast items that may not be needed. items that may not be needed.

Algorithm 1 to handle data push and data pull Algorithm 1 to handle data push and data pull ––Adaptive broadcast scheduling algorithmAdaptive broadcast scheduling algorithmAdaptive broadcast scheduling algorithmAdaptive broadcast scheduling algorithm

1.1. Two potential ways to construct a broadcast. Two potential ways to construct a broadcast. 2.2. New items may be either added to the algorithm or may replace less important New items may be either added to the algorithm or may replace less important

data items.data items.3.3. A global network where all servers in a region know the location and power of all A global network where all servers in a region know the location and power of all

other servers in the region and full replication of the database is assumed.other servers in the region and full replication of the database is assumed.4.4. Periodically, each server broadcasts its location and power level. This begins the Periodically, each server broadcasts its location and power level. This begins the

broadcast cycle [9]. This is a soft realbroadcast cycle [9]. This is a soft real--time system.time system.55 Th d dli f d t d li Th d dli d t d t iTh d dli f d t d li Th d dli d t d t i5.5. There are deadlines for data delivery. The deadlines were used to determine There are deadlines for data delivery. The deadlines were used to determine

which data request to service although no penalty for missing a deadline was which data request to service although no penalty for missing a deadline was mentioned.mentioned.

6.6. There is a leader protocol that selects the server in a region with the greatest There is a leader protocol that selects the server in a region with the greatest remaining power. remaining power. g pg p

7.7. The leader coordinates the broadcast responsibilities of other servers in its area of The leader coordinates the broadcast responsibilities of other servers in its area of influence. influence.

8.8. The lead server determines which portion of a broadcast each server transmits.The lead server determines which portion of a broadcast each server transmits.9.9. The power level of each server drives this broadcast assignment. The power level of each server drives this broadcast assignment. 10.10.The server with the least power transmitted the most important data items.The server with the least power transmitted the most important data items.

DisadvantageDisadvantage

1.1. Initial algorithm has a potentially large communication overhead, servers with no Initial algorithm has a potentially large communication overhead, servers with no clients still broadcast.clients still broadcast.

2.2. Less popular items may be starve or be broadcast too late.Less popular items may be starve or be broadcast too late.

Algorithm 2 to handle data push and data pullAlgorithm 2 to handle data push and data pull1.1. Utilizes a popularity factor (PF).Utilizes a popularity factor (PF).2.2. The PF is a measure of the importance of a data item. The PF is a measure of the importance of a data item. 3.3. The PF increases each time a request is made for a data item. The amount of time The PF increases each time a request is made for a data item. The amount of time

i th t d l ff t th PFi th t d l ff t th PFsince the request was made also affects the PF.since the request was made also affects the PF.4.4. If it has been too long, the need to broadcast the item may be gone.If it has been too long, the need to broadcast the item may be gone.5.5. This factor is called the Resident Latency (RL) and is system and scenario specific. This factor is called the Resident Latency (RL) and is system and scenario specific.

The PF decreases whenever a request exceeds the RL value.The PF decreases whenever a request exceeds the RL value.66 The PF is used to assist in the building of relevant broadcasts and includes RL inThe PF is used to assist in the building of relevant broadcasts and includes RL in6.6. The PF is used to assist in the building of relevant broadcasts and includes RL in The PF is used to assist in the building of relevant broadcasts and includes RL in

order to make allowances for the movement of nodes.order to make allowances for the movement of nodes.7.7. When the PF of broadcast items is high, the probability of a broadcast that serves When the PF of broadcast items is high, the probability of a broadcast that serves

maximum needs increases.maximum needs increases.8.8. If a server has not received any requests for a certain number of broadcasts, it will If a server has not received any requests for a certain number of broadcasts, it will y q ,y q ,

sleep rather than broadcast to an empty audience. sleep rather than broadcast to an empty audience. 9.9. Finally, to localize data delivery, the lead server assigns each server the amount of Finally, to localize data delivery, the lead server assigns each server the amount of

data to broadcast but not the items to broadcast.data to broadcast but not the items to broadcast.10.10. To deal with insufficient power levels, the servers rebroadcast the previous index and To deal with insufficient power levels, the servers rebroadcast the previous index and

broadcast if they have insufficient power to build a new broadcastbroadcast if they have insufficient power to build a new broadcastbroadcast if they have insufficient power to build a new broadcast.broadcast if they have insufficient power to build a new broadcast.

Disadvantages :Disadvantages :

11 Servers can be assigned a broadcast larger than their power levels would permitServers can be assigned a broadcast larger than their power levels would permit1.1. Servers can be assigned a broadcast larger than their power levels would permit.Servers can be assigned a broadcast larger than their power levels would permit.2.2. Power and bandwidth is also wasted with duplication.Power and bandwidth is also wasted with duplication.

Data replication Data replication –– Data correlationData correlationMANETs are often constructed to support cooperative work in MANETs are often constructed to support cooperative work in environments without network infrastructures.environments without network infrastructures.Data replication might cause a situation whereby a node requests two Data replication might cause a situation whereby a node requests two correlated data items at the same time although it can access only one of correlated data items at the same time although it can access only one of g yg ythem.them.If this situation frequently occurs, the data accessibility of the whole system If this situation frequently occurs, the data accessibility of the whole system deteriorates.deteriorates.In a real environment, the correlation among data items can be usually In a real environment, the correlation among data items can be usually , g y, g yknown by recording the access log at each node and periodically estimating known by recording the access log at each node and periodically estimating it.it.

Three replication allocation methods (proposed by [1])Three replication allocation methods (proposed by [1])p (p p y [ ])p (p p y [ ])1.1. SAF (Static Access Frequency): SAF (Static Access Frequency): Only the access frequency to each data item Only the access frequency to each data item

is taken into account.is taken into account.2.2. DAFN (Dynamic Access Freq. and Neighborhood): DAFN (Dynamic Access Freq. and Neighborhood): The access frequency to The access frequency to

each data item and the neighborhood among nodes are taken into account.each data item and the neighborhood among nodes are taken into account.33 DCG (D i C ti it b d G i )DCG (D i C ti it b d G i ) Th f t hTh f t h3.3. DCG (Dynamic Connectivity based Grouping): DCG (Dynamic Connectivity based Grouping): The access frequency to each The access frequency to each

data item and the whole network topology are taken into account.data item and the whole network topology are taken into account.

SAF methodSAF methodEach mobile host allocates replicas of N data items in descending order of the access frequencies.At the time of replica allocation, a mobile host may not connect to another mobile host which has an original or a replica of a data item that the host should allocate. In this case, the memory space for the replica is retained freethe memory space for the replica is retained free.The replica is created when a data access to the data item succeeds or when the mobile host connects to another mobile host which has the original or the replica at a relocation period.In the SAF method, mobile hosts do not need to exchange information with each other for replica allocation.Moreover, replica relocation does not occur after each mobile host allocates all necessary replicas.

AdvantageAdvantage

allocates replicas with low overhead and low traffic.

DisadvantageDisadvantage– Since each mobile host allocates replicas based on only the access frequencies to data items,

mobile hosts with the same access characteristics allocate the same replicas.– However, a mobile host can access data items or replicas held by other connected mobile hosts,

and thus it is more effective to share many kinds of replicas among them.

Gives low data accessibility when many mobile hosts have the same or similar access characteristics.

DAFN methodDAFN methodThe DAFN method eliminates the replica duplication among neighboring mobile hosts.First, this method preliminary determines the replica allocation in the same way as the SAF method.Then, if there is replica duplication of a data item between two neighboring mobile hosts, a mobile host with lower access frequency to the data item changes the replica to another replica. Since the neighboring status changes as mobile hosts move the DAFN method is executed at everySince the neighboring status changes as mobile hosts move, the DAFN method is executed at every relocation period.At a relocation period, a mobile host may not connect to another mobile host which has an original or a replica of a data item that the host should allocate. In this case, the memory space for the replica is temporary filled with one of replicas that have been allocated since the previous relocation period but are not currently selected for allocation. This temporary allocated replica is chosen among the possible

li h th f t th li (d t it ) i th hi h t th If th i treplicas where the access frequency to the replica (data item) is the highest among them. If there is not a possible replica to be temporary allocated, the memory space is retained free. When a data access to the data item whose replica should be allocated succeeds, the memory space is filled with the proper replica.

AdvantageAdvantageData accessibility is expected to be higher than that in the SAF method.

Disadvantage– Does not completely eliminate replica duplication among neighboring hosts because it only executes the elimination

process by scanning the network once based on the breadth first searchprocess by scanning the network once based on the breadth first search.– if the network topology changes during the execution of this method, the replica relocation cannot be done at

mobile hosts over disconnected linksBoth the overhead and the traffic are higher than the SAF method because at each relocation period,

mobile hosts exchange information and relocate replicas.

DCG MethodDCG MethodThe DCG method shares replicas in larger groups of mobile hosts than the DAFN method that shares replicas among neighboring hosts. In order to share replicas effectively, each group should be stable, i.e., the group is not easily divided due to changes of network topology. From this viewpoint the DCG method creates groups of mobile hosts that are biconnectedFrom this viewpoint, the DCG method creates groups of mobile hosts that are biconnected components[1] in a network. Here, a biconnected component denotes a maximum partial graph which is connected (not divided) if an arbitrary node in the graph is deleted.By grouping mobile hosts as a biconnected component, the group is not divided even if one mobile host disappears from the network or one link is disconnected in the group, and thus it is considered that the group has high stability.At a relocation period, a mobile host may not connect to another mobile host which has an original or a replica of a data item that the host should allocate.In this case, in the same way as the DAFN method, the memory space for the replica is temporary filled with another replica and it is filled with the proper one when a data accesstemporary filled with another replica, and it is filled with the proper one when a data access to the corresponding data item succeeds.

Advantage– Since many kinds of replicas can be shared, the data accessibility is expected to be higher.y p y p g

Disadvantage– However, since the DCG method consists of three steps; (i) broadcasting host identifiers, (ii)

determining the replica allocation, and (iii) notifying it to all hosts in the group, this method takes the largest time among the three methods to relocate replicas.the largest time among the three methods to relocate replicas.

Access to Global State InformationAccess to Global State Information

Update DiffusionUpdate Diffusion Query diffusionQuery diffusion

–– Sensed changes cause updates to be Sensed changes cause updates to be propagated to a database, which is propagated to a database, which is typically replicated over a number of typically replicated over a number of nodes.nodes.

–– Entire state information is stored in theEntire state information is stored in the

–– State information only stored in the State information only stored in the nodes where it has been sensed.nodes where it has been sensed.

–– For state retrieval an application For state retrieval an application broadcasts or geocasts a query broadcasts or geocasts a query specifying the requested statespecifying the requested state–– Entire state information is stored in the Entire state information is stored in the

databasedatabase–– Applications access an available Applications access an available

database copy for state retrieval.database copy for state retrieval.

DisadvantagesDisadvantages

specifying the requested state specifying the requested state informationinformation

–– State information matching the query is State information matching the query is sent back to the applicationsent back to the application

DisadvantagesDisadvantagesDisadvantagesDisadvantages

1.1. Danger of inconsistenciesDanger of inconsistencies

Paper 10 has derivation of fewPaper 10 has derivation of few

DisadvantagesDisadvantages

1.1. For partitioned networks the availability For partitioned networks the availability of state information is poor since each of state information is poor since each state item is stored on a single node state item is stored on a single node onlyonlyPaper 10 has derivation of few Paper 10 has derivation of few

algorithms which help in taking care of algorithms which help in taking care of this problem.this problem.

onlyonly2.2. Applications need to learn about state Applications need to learn about state

changes as fast as possible.changes as fast as possible.

ReferencesReferences

[1] T. Hara, ``Effective replica allocation in ad hoc networks for improving data accessibility,'' Proc. IEEE [1] T. Hara, ``Effective replica allocation in ad hoc networks for improving data accessibility,'' Proc. IEEE Infocom 2001, pp.1568Infocom 2001, pp.1568--1576, 2001.1576, 2001.[2] T. Hara, ``Replica allocation methods in ad hoc networks with data update,'' ACM[2] T. Hara, ``Replica allocation methods in ad hoc networks with data update,'' ACM--Kluwer Journal Kluwer Journal on Mobile Networks and Applications Vol 8 No 4 pp 343on Mobile Networks and Applications Vol 8 No 4 pp 343--354 2003354 2003on Mobile Networks and Applications, Vol.8, No.4, pp.343on Mobile Networks and Applications, Vol.8, No.4, pp.343--354, 2003.354, 2003.[3] T. Hara and S.K. Madria, ``Dynamic data replication schemes for mobile ad[3] T. Hara and S.K. Madria, ``Dynamic data replication schemes for mobile ad--hoc network based on hoc network based on aperiodic updates,'' Proc. Int'l Conf. on Database Systems for Advanced Applications (DASFAA 2004), aperiodic updates,'' Proc. Int'l Conf. on Database Systems for Advanced Applications (DASFAA 2004), pp.869pp.869--881, 2004. 881, 2004. [4] T. Hara, N. Murakami, and S. Nishio: ``Replica Allocation for Correlated Data Items in Ad[4] T. Hara, N. Murakami, and S. Nishio: ``Replica Allocation for Correlated Data Items in Ad--Hoc Hoc Sensor Networks,'' ACM SIGMOD Record, Vol.33, No.1, pp.38Sensor Networks,'' ACM SIGMOD Record, Vol.33, No.1, pp.38--43, 2004.43, 2004.Sensor Networks, ACM SIGMOD Record, Vol.33, No.1, pp.38Sensor Networks, ACM SIGMOD Record, Vol.33, No.1, pp.38 43, 2004.43, 2004.[5] H. Hayashi, T. Hara, and S. Nishio, ``Cache Invalidation for Updated Data in Ad Hoc Net[5] H. Hayashi, T. Hara, and S. Nishio, ``Cache Invalidation for Updated Data in Ad Hoc Net--works,'' works,'' Proc. Int'l Conf. on Cooperative Information Systems (CoopIS'03), pp.516Proc. Int'l Conf. on Cooperative Information Systems (CoopIS'03), pp.516--535, 2003.535, 2003.[6] G. Cao, L. Yin, C.R. Das, ``Cooperative Cache[6] G. Cao, L. Yin, C.R. Das, ``Cooperative Cache--Based Data Access in Ad Hoc Networks,'' IEEE Based Data Access in Ad Hoc Networks,'' IEEE Computer Magagine, Vol.37, No.2, pp. 32Computer Magagine, Vol.37, No.2, pp. 32--39, 2004.39, 2004.[7] L.D. Fife and L. Gruenwald, ``Research issues for data communication in mobile ad[7] L.D. Fife and L. Gruenwald, ``Research issues for data communication in mobile ad--hoc networkhoc network[7] L.D. Fife and L. Gruenwald, Research issues for data communication in mobile ad[7] L.D. Fife and L. Gruenwald, Research issues for data communication in mobile ad hoc network hoc network database systems,'' ACM SIGMOD Record, Vol.32, No.2, pp.42database systems,'' ACM SIGMOD Record, Vol.32, No.2, pp.42--47, 2003.47, 2003.[8] G. Karumanchi, S. Muralidharan, and R. Prakash, ``Information dissemination in partitionable [8] G. Karumanchi, S. Muralidharan, and R. Prakash, ``Information dissemination in partitionable mobile ad hoc networks,'' Proc. Symposium on Reliable Distributed Systems (SRDS'99), pp.4mobile ad hoc networks,'' Proc. Symposium on Reliable Distributed Systems (SRDS'99), pp.4--13, 13, 1999.1999.[9] J. Luo, J.P. Hubaux, and P. Eugster, ``PAN: Providing reliable storage in mobile ad hoc networks [9] J. Luo, J.P. Hubaux, and P. Eugster, ``PAN: Providing reliable storage in mobile ad hoc networks [ ] g g g[ ] g g gwith probabilistic quorum systems,'' Proc. ACM MobiHoc 2003, pp.1with probabilistic quorum systems,'' Proc. ACM MobiHoc 2003, pp.1--12, 2003.12, 2003.[10] K. Rothermel, C. Becker, and J. Hahner, ``Consistent update diffusion in mobile ad hoc [10] K. Rothermel, C. Becker, and J. Hahner, ``Consistent update diffusion in mobile ad hoc networks,'' Technical Report 2002/04, Computer Science Department, University of Stuttgart, 2002.networks,'' Technical Report 2002/04, Computer Science Department, University of Stuttgart, 2002.[11] F. Sailhan and V. Issarny, ``Cooperative caching in ad hoc networks,'' Proc. Int'l Conf. on Mobile [11] F. Sailhan and V. Issarny, ``Cooperative caching in ad hoc networks,'' Proc. Int'l Conf. on Mobile Data Management (MDM'03), pp.13Data Management (MDM'03), pp.13--28, 2003.28, 2003.[12] K. Wang and B. Li, ``Efficient and guaranteed service coverage in partitionable mobile ad[12] K. Wang and B. Li, ``Efficient and guaranteed service coverage in partitionable mobile ad--hoc hoc networks,'' Proc. IEEE Infocom'02, Vol.2, pp.1089networks,'' Proc. IEEE Infocom'02, Vol.2, pp.1089--1098, 2002.1098, 2002.[13] [13] http://www3.ietf.org/proceedings/00mar/47thhttp://www3.ietf.org/proceedings/00mar/47th--ietfietf--00mar00mar--96.html96.html