Security in a delay tolerant network is an area of focus in recent years and many researcher proposed various technologies for security enhancement. Delay tolerant network is an architecture specially designed for communication where delay and frequent disconnection occurs like interplanetary communication. This paper discuss the work related to delay tolerant network routing protocols, security, advantages, disadvantages and others.
Keywords: Interplanetary communication,.Introduction:
The idea of Delay Tolerant Network (DTN) was taken from interplanetary Networks (IPN), which was started in 1970s. IPN was invented to communicate between earth and mars. The DTN is a wireless ad-hoc network which tolerates the intermittent connectivity. DTN can also be defined as intermittently connected wireless ad-hoc network 1 that can tolerate the longer delays, intermittent connectivity and prevent data from being lost by using store-carry-forward approach. Intermittent Connectivity can be defined as the sudden change of state (up/down) of any communication link between the nodes. The Store-carry-forward approach enables the nodes to take the message, store it in buffer and forward the same whenever new node comes in its communication range. In DTN 2, nodes have minimal knowledge about the network scenario. The DTN allows the communication between the wireless nodes in the scenario where end to end connectivity could never be achievable or when the delay associated in relaying data could be very high. The operation of DTN makes use of Bundle Protocol (BP), positioned above the TCP protocol in the protocol architecture stack of DTN. The main functions a BP can provide are 3The application areas of DTN are challenged environments like military battlefields, deep under water communication, natural hazard affected areas or remote area social networking etc.
The advantage of DTN over other wireless networks is that DTN can tolerate intermittent connectivity and assure the data delivery even with very limited knowledge of network.
Routing in DTN:
In traditional networks, the routing of packets between a pair of nodes aims to select the optimal path with minimum cost incurred. In these networks an optimal route needs to be established before the actual transmission of message. As in DTN the end to end route can never be achieved so t hop by hop, in which the selection of next hop is done dynamically as per the application scenario as well as the algorithm used. In general, when a node receives any message then as per the algorithm, that node will search the good relay node to which it can forward the bundle. The transmission of message in DTN can either be done by replicating the message or forwarding it, that depends on the type of algorithm used.
i) Flooding Based: This type of routing strategy can be opted even when the nodes have no knowledge about the nodes in the network
ii) Forwarding Based: This type of routing takes place when nodes have some relevant knowledge about the other nodes in the network. In this type of routing no node will generate replicates of the messages.
1. Key management: PKI is highly impractical in DTN, because it requires key distribution through online servers or an online service which is quiet impossible in DTNs because of the disruption.
2. Analyzing the traffic: The extent up to which analysis has to be done and how to make it less resource exhaustive remains an open issue.
3. Multicast security and handling replays: DTN allows unlimited number of registrations in an endpoint, even if that node is singleton, more than one node can come and register and receive the messages meant for that node. Handling replays remain an open issue because of delays in DTNs. 4
4. Flexibility: Flexibility remains an open issue. The bundle in bundle encapsulation mechanism for confidentiality has high complexity and requires high
Tuan le,Mario Gerla et al4present social based communication scheme under different mobility model.For multicating tree branching technique and single copy model are used which menas every destination node has its own message copy.For anycasttwo metrics are present ,AEDM and ASDM.ASDM is more conservative as compared to ADEM.The NS-3 simulator is used for performance evaluation.Simulation result show that presented schema provides low delay,low cost and high delivery ratioas compared to EBMR,Epidemic,UBA and ADEM.
Alessandro mei,Julinda stefa et al5 present message forwarding schema in social mobile wireless snetwork in assuming that all nodes in the network is selfish.Give to Get forwarding consists three phases:Message generation ,message relays and testing.Message generation executes when one node have message to send pass to some other nodein the network.After message generated source node transfer the messageto the nodes its meet.When the receiver node receive message and pass to the proof of sending to the sender.Affter thr receiving proof every time node have to showthe proof and node fails ,theproof of misbehaving is broadcast.Only when two proofs are collected by node ,message can be discarded by node’s memory.Proposed algorithm good in terms of message delay ,success rate and cost.
Pan Hui,Jon Crowcroft,Elko Yoneki et al6introduce bubble rape:Social based forwarding in delay tolerant network,for designing this hybrid algorithm,centrality and community detection method called K-CLIQUE community detection is used. As per simulation result bubble is designed to work better with a hierarchical community structure. It improves the parameter no of message copies,no of hops, time to live, delivery ratio,delivery cost.
S.Ramya,K.Laxmi Prabha,S.Selvan et alpresent mobility prediction and forwarding routing in delay tolerant network.Proposed system consists phases which are as follows:cluster head selection,receive only,scheduling,packet sending,mobility prediction.Cluster head is used for managing nodes and communicating with other cluster head.Proposed work is done in network simulator2.As persimulation result packet delivery ratio is high as compared to other DTN protocols.
Zenging Lu,Xion Sun et al7proposed skeleton in mobile social network.Skeleton is mainly formed for predicting node contacts and managing the node.Skeleton is based on the social property of nodes like best friends,rank etc.Skeleton is tree structure which makes the communication more reliable.As per simulation resultskeleton gives more efficient resuls than existing community based algorithm.
Moman Kashif M,,Prof V.S.Kadamet al6proposed improved collaborative watchdog system for detecting selfish node in manet.Selfish nodevdegrades the performance of the network by not taking part in the communication system for consume their resources.So it is very important to detect selfish node in the network and remove it from the system.In this paper proposed a method to detect the selfish node based on trust and reputation of every node.For reputation using Buyesian estimation .Baye’s theorem is as follows:
P(?i/y)=p(y/?i)p(?i) i=1npy?ip?iAs per result,this scema is highly robust,efficient and improve performance of the mechanism.
Jianfeng Guan,Qi Chu,Ilsan You et al8proposed multi spray and wait routing algorithm for disruption tolerant network.Different from traditional routing which is based on end to end path from source to destination ,DTN use store carry forward mechanism.In this paper proposed a social relationship based spray and wait routing to improve performance by considering buffer managementand social parameters.In proposed schema timeout detection mechanism is used to solve blind spot problem anf buffer management for reduce the overhead.As per its functionality social parametes is used for predict path.By comparison with traditional algorithms,it shows that proposed algorithm improve message delivery ratio,reduce the overhead and decrease the buffer time.
Husna Taj,Kampe Shilp et alintroduced detection selfish node using a collaborative contact based watchdog.Data transmission in the network is based on the behavior of node.If node can cooperative in nature than they send the packet but uncooperative nature of nodes degrades the performance of the network.Foe detecting selfish node COCOWAmodel is introduced which use markov chain model to evaluate detection time.This techniq will reduce the time of detecting selfish node as well as reduce the effect of malicious node.
Aminu 4 proposed a rebroadcast probability function which takes into account about the value of the packet counter together with some key simulation parameters(i.e., network topology size, transmission range and number of nodes) to determine the appropriate rebroadcast probability for a given node. The rebroadcast probability of a node is computed based on these parameters. Compared to the other schemes, simulation results have revealed that counter Function achieved superior saved rebroadcast and end-to-end delay without sacrificing reach ability in medium and dense networks.
Ould-Khaoua 5 proposed two new probabilistic route discovery methods. They are Adjusted Probabilistic route discovery (AP) and Enhance Adjusted Probabilistic route discovery (EAP).This addresses the broadcast storm problem in the existing on-demand routing protocols. The forwarding probability is determined by taking into account about the local density of the sending node. In order to reduce the routing overhead without degrading the network throughput in dense networks, the forwarding probability of nodes located in sparse areas is set high while it is set low at nodes located in dense areas. EAP-AODV reduces overhead by 71% while APAODV reduces the overhead by 55%.
Priyanka A Deokar et alproposed a global watchdog for detecting selfish node in the network.Watchdog is a monitor that keeps record of activities of the network.If the receiver not forward packet within a time,it mark that node as selfish node and inform rest of the nodes and remove it from the system.
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