1 University of Delhi 2 University of Delhi 3 Ryerson University

1. Routing in Opportunistic Networks Chapter 13:Routing Protocols in Infrastructure-less Opportunistic NetworksSanjay Kumar Dhurandher1, Deepak Kumar Sharma2, Isaac Woungang3,and Shruti Bhati1 • 1University of Delhi • 2University of Delhi • 3 Ryerson University

2. Opportunistic Networks(OppNets)Characteristics & Challenges • Opportunistic Network [1] is one of the most interesting and recent evolutions of Mobile Ad-hoc Networks (MANETs). • The traditional routing algorithms used for MANETs and Internet are not applicable here as they first establish a path between the source and the destination before the actual message transfer which is not possible in case of OppNets [2,3]. • They exhibit a store-carry and forward approach. If a suitable node is not found, the node simply stores the message and carries it through the network until a better node or destination is found [4,5].

3. Opportunistic Networks(OppNets)Characteristics & Challenges (Contd.) • OppNets are enabled to deliver messages even when there is no connected path between the source and the destination. • One key characteristic of opportunistic networks is that they are essentially delay tolerant in nature asthey can handle large delays in message delivery from the source to the destination. • OppNets share similar routing algorithms as used in Delay Tolerant Networks [6,7]. • If a suitable node is not found, the node simply stores the message and carries it through the network until a better node or destination is found [5].

4. Types of protocols for routing in OppNets • The routing protocols in OppNets are divided into two categories namely the infrastructure based and the infrastructure-less protocols [8] • Infrastructure based protocols: These protocols make use of some form of infrastructure to opportunistically forward messages. • Base stations and access points are often involved in the routing and forwarding of the messages. • Infrastructure-less protocols: These protocols are best suited for the flat ad-hoc networks. • They only make use of the mobility of the nodes and the contact opportunity between them in order to route the messages. • They make no previous assumptions about the network topology and all the nodes behave same in the network and are given the same priority

5. OppNets Routing Protocols Direct Transmission [9]: • The source node does not forward the message to the intermediate nodes, but stores it in the buffer until it comes in direct contact with the destination node. • On encountering the destination node, the message is directly given to the destination. • Advantages • This protocol utilizes minimum network resources, and cannot suffer from the problems of network clogging. • The protocol is very simple and fairly easy to deploy. • Disadvantages • It is likely to suffer from heavy delays as source node may not encounter the destination node for longer period of times. • If a node failure occurs, the message can be lost since there is only one cope available in the network.

6. Example scenario of Direct Transmission

7. OppNets Routing Protocols (Contd.) First Contact [10]: • It is a routing scheme[10] that does not predict, utilize or assume any properties of the network or the nodes. • The carrier node forwards the message to any node that comes into contact with it. • Advantages • It does not make any assumptions about the network and thus can be implemented easily. • This scheme can be used for multicast messages. • Disadvantages • The scheme can lead to huge message delivery delays. • Indiscriminate spreading of messaging can lead to network clogging as well as packet dropping which are highly unacceptable

8. Example Scenario of First Contact

9. OppNets Routing Protocols (Contd.) Epidemic Protocol [11]: • This protocol [11] makes minimal assumptions about the network and is guaranteed to deliver the message to the destination. • It aims to distribute messages to other nodes within connected portions of the network. • These nodes then come into contact with another portion of the network and the message spreads like a disease (epidemic). • Advantages • The protocol makes minimum assumptions about the network topology and it is fairly easy to deploy and understand. • Out of all the opportunistic network protocols, epidemic has the least overhead in terms of calculations for determining the next hop. • The message delivery probability is very high in this protocol.

10. OppNets Routing Protocols (Contd.) Epidemic Protocol [11]: • Disadvantages • The memory and resource consumption is very high in this protocol, as the message is passed to all the nodes indiscriminately. • Considerable amount of computation occurs at every node before exchanging the messages even in the case of nodes that might have the same messages. Hence some amount of memory is wasted. • Even when a message is received at the destination, some nodes still continue passing on the messages which wastes resources.

11. Example Scenario of Epidemic Routing

12. OppNets Routing Protocols (Contd.) Spray and wait [12]: • This protocol[12] is an extension to the epidemic routing protocol. • It aims to reduce the overhead of flooding which often causes network congestions and indiscriminate usage of the network resources. • One way of doing so is to only forward a copy with some probability. • The probability is the utility of every node based on the timer indicating the time elapsed since the two nodes last encountered the node maintaining the record. These are indirectly the relative node locations • There are two phases in the forwarding process – • Spray phase– Every message generated is spread randomly to L relay nodes i.e. L copies of message are created. • Wait phase– If the destination is not found in spray phase, the nodes then wait for direct transmission.

13. OppNets Routing Protocols (Contd.) • Binary Spray and Wait– It is a variation of the spray and wait protocol. The source starts initially with L copies of the message. • The source or any relay node that has n>1 message copies hands over n/2 copies to any other node (without message copy) in the network and keeps the remaining copies n/2 with itself. • Advantages • The protocol reduces the memory inefficiencies of epidemic routing by limiting the amount of flooding caused in the network. • Disadvantages • Even though L is chosen to limit flooding, the protocol still suffers from delays and resource consumption issues. • The message delivery probability depends highly on the value of L chosen, which is assumed on the basis of the network parameters.

14. Example Scenario of Spray and Wait

15. OppNets Routing Protocols (Contd.) Spray and Focus [13]: • This protocol [13] overcomes the shortcomings of simple spraying algorithms and is better than the flooding. • The scheme again has two phases – • Spray phase– When a new message is generated at the source node, it creates L forwarding tokens for this message. • When a node meets another node with no message copy, the first node copies the message to the second node along with n/2 forwarding tokens. • When a node has only one forwarding token then it forwards the message according to the Focus phase. • Focus phase –Forwarding is done based on some criterion. These decisions are based on a set of timers that record the time since the two nodes last saw each other. Node i maintains a timer Ti(j) for every other node j which records time elapsed since the two nodes last saw each other.

16. OppNets Routing Protocols (Contd.) Spray and Focus [13]: • Advantages • Owing to refined selection criterion, the protocol has higher message delivery rates. • Fewer copies are spread into the network as compared to the spray and wait protocol. • Disadvantages • The protocol suffers from a larger overhead of resource consumption. • Protocol suffers in case of sparse networks as the time taken by nodes to meet will be greater and there will be fewer opportunities to forward the data.

17. OppNets Routing Protocols (Contd.) Adaptive Fuzzy Spray and Wait [14]: • This protocol [14] has been proposed as an improvement over the popular spray based routing schemes. • It smartly integrates the overheads and buffer management policies into an adaptive protocol that includes local network parameters estimation. • The algorithm can be summarized in the following few steps: • The node on encountering other nodes divides the values of L by 2 and updates it in the message before passing it on. • The node passes on all the copies to the nodes it encounters except the last copy which is passed on as direct transmission. • The messages in the buffer are sorted by a priority decided by a Fuzzy decision making function. • When the buffer is full, the messages are dropped according to the priority level i.e. the oldest first.

18. OppNets Routing Protocols (Contd.) Adaptive Fuzzy Spray and Wait [14]: • Forward Transmission Count and Message Size are two indicators that help in determining the prioritization quantity. The dropping policy used for the algorithm is random instead of drop least priority scheme so that it remains fair to all the messages. • Advantages • The scheme has better delivery performance than simple spray based techniques. • Appropriate and fair buffer management schemes used in this protocol avoid the clogging of the network. • Disadvantages • Large messages might get delayed if there are a higher number of small messages. • If all the messages are of approximately the same size and a constant indicator of size is used, the size of message becomes irrelevant to priority

19. OppNets Routing Protocols (Contd.) PRoPHET [15]: • Probabilistic Routing Protocol[15] using History of Encounters and Transitivity (PRoPHET) , assumes that instead of moving randomly the nodes in a network move in a predictable fashion wherein patterns are likely to repeat themselves. • This information can be used to improve the routing performance. • Each node before sending a message, calculates a probabilistic metric called Delivery Predictability for each known destination in form of vectors. • This Delivery Predictability is assumed to be P(a,b) {0,1} i.e. the probability of every node a to meet any other node b in the network.

20. OppNets Routing Protocols (Contd.) PRoPHET [15]: • Advantages • Simulation results of this protocol show that it has less message exchanges, less communication overhead, less delay, and higher delivery success rate as compared to the epidemic routing. • The protocol is highly suited to human mobility scenarios. • Disadvantages • Resource consumption occurs in terms of calculations occurring at each node. • Memory is needed to store the probability tables generated by the protocol. • Packets may be dropped consistently when forwarded to a few concentrated nodes due to FIFO queuing nature of PRoPHET.

21. OppNets Routing Protocols (Contd.) PRoPHET+ [16]: • This protocol [16] is an extension to the PRoPHET protocol that uses only delivery predictabilities of the nodes to decide the next best carrier for the message. • This scheme uses several other parameters such as Buffer, Power, Bandwidth, Location and Popularity into consideration to reduce the packet loss and transmission delay. • Advantages • Packet dropping and loss are significantly reduced as compared to PRoPHET by monitoring the power and popularity of the node. • The protocol takes into account several parameters other than delivery predictability which strengthens the best node probability. • Disadvantages • Too many calculations need to be done at each node. • Uncooperative nodes can cause a problem for the sender

22. OppNets Routing Protocols (Contd.) HiBOp [17]: • The History Based Routing Protocol for Opportunistic Networks (HiBOp) [17] aims at effectively utilizing the context information of the node in order to decrease the overhead of flooding. • The Current Context (CC) of a user is a snapshot of the local environment of the user. • It is stored in the form of Identity Tables (ITs). • Every node also stores a History table that stores values from the ITs seen by the node in the past. • Every value has a Continuity Probability (Pc), Heterogeneity (H) and Redundancy (R) counters associated with them.

23. OppNets Routing Protocols (Contd.) HiBOp [17]: • The forwarding process in HiBOp is made of three phases: • Emission Phase:HiBOp injects the message into the network through flooding to an appropriate number of nodes by creating message replicas for reliability. • The number of neighbors (K) to which the message is forwarded by the sender is calculated using a formula that takes into account the probability of delivering the message to the destination. • The value of K should be minimized in order to minimize the joint loss probability below a certain threshold. • Forwarding Phase: It uses the node’s mobility and contacts to take the message closer to the destination. • It uses two quantities .The forwarding of message to a certain node during its journey in the network is determined by the match between the sender information and the context information of the nodes. • Delivery predictability of a node is also taken into account before passing on the message. At each node the delivery probability is calculated using node IT, its CC and its History table.

24. OppNets Routing Protocols (Contd.) HiBOp [17]: • Delivery Phase: When an intermediate node finds the destination, the message is delivered to it and the process stops. • Advantages • This protocol stores the largest amount of context information among all context base protocols, so it can fully exploit the advantages of context information. • The protocol is very suitable for human mobility models that generally follow a particular pattern. • The protocol reduces network clogging by drastically limiting the number of copies spread in the network. • Disadvantages • The IT, CC, History table and Repository table require a large amount of memory space on every node. • The calculations done every time at every node can significantly reduce the amount of time left for message exchange.

25. OppNets Routing Protocols (Contd.) CEPMF [18]: • This protocol [18] uses the content of the messages to relay and deliver them to their destination. • The node that generates the messages is called the publisher and the node that wants a message similar in content to the message being sent is called subscriber. • If subscribers demand a message of a particular type of content, they spray the network with their interests all over the network in the form of predicates. • The entire protocol can be divided into two steps- • Predicate propagation: The subscriber spreads its interests into the network by spraying predicates. The Spray and Wait scheme is used for sending the predicates. • Message Forwarding: Each node has a table carrying the message and tagged to it epvalue. At source node the value is zero. • When a node transfers message to a node carrying the message’s epvalue in its table, the acknowledgement tells the source to stop sending until it is out of its range.

26. OppNets Routing Protocols (Contd.) CEPMF [18]: • Advantages • The protocol can be safely used for multicast messaging situations. • It does not rely on the geographic location of the nodes and thus can be used in cases where GPS is not enabled. • Disadvantages • A node may still receive a particular message which it does not want, if its demands are partially similar to the predicates of the message. • There might be high privacy and rick issues associated with the content transparency.

27. Example Scenario of CEPMF

28. OppNets Routing Protocols (Contd.) Robust Proactive Routing Protocol [19]: • This protocol[19] has been proposed as a proactive scheme to deliver messages in the highly disconnected scenarios present in OppNets. • It is an adaptive protocol that uses the opportune contacts between the nodes to determine the neighborhood information for each node and use that to deliver the messages. • The basic principle is that a node can determine the predictability information and connectedness information using past history. • The nodes do not forward data randomly instead they have a well studied and selected next hop node.

29. OppNets Routing Protocols (Contd.) Robust Proactive Routing Protocol [19]: • Advantages • The following protocol is suited to Human mobility models since it can show better results for predictable movement. • It reduces the overhead of flooding by limiting the next hop for node and only selects the best candidate. • Disadvantages • There is considerable overhead in exchanging and storing tables at each node.

30. OppNets Routing Protocols (Contd.) Repository Based Forwarding Protocol [20]: • This protocol [20] makes distinction between the types of nodes in the network and uses them to deliver the message to its destination. • It argues that assuming all nodes to be Mobile Nodes is not correct in a model where nodes move in a predictable fashion (Human mobility model). • Some nodes are likely to be in a place more often than others. Hence commonly visited and shared location are assigned to be Fixed Nodes. • The Mobile Nodes are characterized by the mobility pattern which in turn has a strong impact on their performance. • Each node has a character table (CT) that defines the node’s home location, communication range, ID and type.

31. OppNets Routing Protocols (Contd.) Repository Based Forwarding Protocol [20]: • When a node meets another node, they exchange their CT tables that describe their characteristics. • Depending on the type one of the nodes initiates the forwarding process. The forwarding process is further divided into two parts: • Message Dispatch: Node initiating communication sends all messages as type tsend either directly (to the target node itself) or indirectly (i.e. through a Fixed Node which eventually forwards it). • Message Collect: Node collects all the messages that have the target_ID set as the node itself. The status flag is checked to prevent from the same message being collected again • Advantages • Fixed nodes can decrease the delivery delays considerably. • Disadvantages • If fixed nodes fail, the entire network will be brought down

32. OppNets Routing Protocols (Contd.) MaxProp [21]: • This protocol [21] assumes that it has no prior knowledge about the network connectivity and uses the local information and opportune movement to select the next best hop for the message delivery. • The protocol has three main components : • Estimating Delivery Likelihood: The protocol aims to find the optimal delivery paths by constructing a directed graph of nodes which are connected by edges [21]. • A variation of Dijkstra’s algorithm is used to determine the shortest path out of available paths at any given point of time. • Complementary Mechanisms:This step describes the priority order in which messages are exchanged when two nodes discover each other. • Managing Buffer: The protocol states that there is a difference between managing limited storage and limited transmission in that the packets sent once can be sent again.

33. OppNets Routing Protocols (Contd.) MaxProp [21]: • Advantages • MaxProp uses Dijkstra’s algorithm to ensure that the lowest cost path is chosen so as to decreases the delivery latency. • Proper buffer management schemes lead to a lowered rate of packet dropping. • Disadvantages • The overhead of table exchange can decrease the effective time for message exchange. • The protocol is not suited for sparse networks, as it will not give a proper connected graph and thus will not satisfy the protocol criteria.

34. OppNets Routing Protocols (Contd.) CAR [22]: • In this protocol[22] , the nodes are assumed to rely on their ‘logical connectivity information’ with other nodes. • They are not aware about the location of the nodes, which are the recipients of the messages they are carrying with them. • Proactive protocol such as DSDV [25] is used to deliver the messages if the recipient node belongs in the same cloud. • Otherwise, the relay nodes are chosen in such a manner that they present the highest delivery probabilities. • The process of prediction and evaluation of context takes care of following things. • Calculation of self delivery probabilities • Table • Local prediction of delivery probabilities at intervals • New message recipient • Message exchange

35. OppNets Routing Protocols (Contd.) CAR [22]: • Advantages • The protocol is uninfluenced by the unavailability of GPS. • The proactive approach highly reduces the overhead of prediction calculation and can deliver message faster if dense networks are present. • Disadvantages • The overhead of table exchange, updating and maintenance can severely reduce the performance. • In absence of a proper buffer management scheme, the messages may be lost.

36. OppNets Routing Protocols (Contd.) Meetings and Visits [23]: • This routing protocol [23] uses the same pair-wise message exchange principle as Epidemic Routing, but improves on the method used to determine which messages to transmit. • Instead of flooding its neighbors, each node uses observation data on the meetings between nodes and visits to locations (hence the name MV) to compute a delivery probability for every other node. • When two nodes meet, the summary vectors contain not only the message identifiers but also the computed delivery probability. • Nodes compare their own and their pair’s values, and only request messages for which their probability is higher.

37. OppNets Routing Protocols (Contd.) Meetings and Visits [23]: • Advantages • The protocol is highly suited to human mobility scenarios as mobility patterns of nodes are stored for routing of the messages. • It uses the techniques from robotic control to obtain high-quality approximations for the optimal solution. • It also limits the number of hops that are required, by calculating an estimation of delivery likelihood assuming an infinite buffer at each peer. • Disadvantages • As it uses FIFO for buffer management at nodes, packets may get dropped consistently when forwarded to a concentrated node. • Considerable overhead occurs in storing the mobility pattern of nodes at regular time intervals.

38. OppNets Routing Protocols (Contd.) Network Coding [24]: • This protocol[24] presents an approach in which a message is encoded into another format before transmission. • The intermediate nodes not only forward but also can combine packets using a given invertible function before forwarding to limit the message flooding. • At the receiver side, as compared to the replication based schemes which rely on successful delivery of each individual data block, this scheme consider the successful delivery of a block only when the necessary number of blocks is received to reconstruct the original data.

39. OppNets Routing Protocols (Contd.) Network Coding [24]: • Advantages • This schemes is more robust against packet losses than replication based schemes when network connectivity is extremely poor, as it consider the successful delivery of a block only when the necessary number of blocks is received to reconstruct the original data. • The number of transmissions is reduced in this approach, and consequently the packet delivery ratio is much higher than the probabilistic forwarding both in dense mobile networks and sparse networks. • Disadvantages • When the network is well connected thisschemes is less efficient due to additional information embedded in the code blocks. • This method leads to additional processing power and memory requirements due to the encoding and decoding process.

40. Tabular Comparison of various protocols

41. Tabular Comparison of various protocols (contd.)

42. Tabular Comparison of various protocols (contd.)

43. Conclusion • In this chapter, we have given a brief outline of a number of routing protocols for infrastructure-less OppNets. • These protocols have been analyzed and compared on the basis of their advantages and disadvantages with respect to a variety of parameters. • This study leads to the identification of some critical and explicit characteristics of each protocol along with their areas of application. • A few main concerns that are reflected in almost all protocols are delivery latency, packet dropping and packet loss, memory management, computation and storage overhead. • The discussed protocols in this chapter implement different techniques to abate the inefficiencies caused due to these factors.

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48. Thanks for your attention!