A Position Based Opportunistic Routing

Published Date: 02 Nov 2017

ABSTRACT

This work addresses the problem of delivering data packets for highly dynamic mobile ad hoc networks in a reliable and timely manner. Most existing ad hoc routing protocols are susceptible to node mobility, especially for large-scale networks. Driven by this issue, an efficient Position-based Opportunistic Routing (POR) protocol is used which takes advantage of the stateless property of geographic routing and the broadcast nature of wireless medium. When a data packet is sent out, some of the neighbor nodes that have overheard the transmission will serve as forwarding candidates, and take turn to forward the packet if it is not relayed by the specific best forwarder within a certain period of time. By utilizing such in-the-air backup, communication is maintained without being interrupted. The additional latency incurred by local route recovery is greatly reduced and the duplicate relaying caused by packet reroute is also decreased. In the case of communication hole, a Virtual Destination-based Void Handling (VDVH) scheme is further proposed to work together with POR. But in case of real time Manets Node Mobility, Communication among the nodes and Energy level are considered. In this thesis work Fuzzy Sets are used along with POR .Fuzzy sets apply some rules while selecting the forwarding nodes. It selects the nodes with high mobility, communication with many number of nodes, and high energy level. So that the Communication Life time increases.

INTRODUCTION:

MOBILE ad hoc networks (MANETs) have gained a great deal of attention because of its significant advantages such as multihop, infrastructure-less transmission. Due to the error prone wireless channel and the dynamic network topology, reliable data delivery in MANETs, is challenging in environments with high mobility. Traditional topology-based MANET routing protocols (DSDV, AODV, DSR)are susceptible to node mobility. The discovery and recovery procedures are also time and energy consuming. Once the path breaks it leads to transmission interruption.Geographic routing (GR) uses location information to forward data packets, in a hop-by-hop routing fashion.Greedy forwarding is used to select next hop forwarder with the largest positive progress toward the destination.. If the node moves out of the sender’s coverage area, the transmission will fail. In GPSR the MAC-layer failure feedback is used to offer the packet another chance to reroute. When node mobility increases the performance will decreases.

The multicast-like routing Strategy is used in opportunistic routing They use link-state-style topology database to select and prioritize the for-warding candidates. Location-aided opportunistic routing directly uses location information to guide packet forwarding. But it is designed for static mesh networks .In Position-based Opportunistic Routing (POR)protocol, which several forwarding candidates cache the packet that has been received using MAC interception. If the best forwarder doesnot forward the packet in certain time slots, suboptimal candidates will take turn to forward the packet . So the data transmission will not be interrupted.Potential multipaths are exploited .In case of communication void Virtual Destination –Based Void Handling (VDVH) Scheme is used. In this paper Fuzzy set along with POR is used to select the forwarding node based on node mobility, communication between nodes and energy level.

In section 2 ,we overview POR.In section 3

POSITION-BASED OPPORTUNISTIC ROUTING

2.1 Overview

The design of POR is based on geographic routing and opportunistic forwarding. The nodes are assumed to be aware of their own location and the positions of their direct neighbors. Neighborhood location information can be exchanged using one-hop beacon or piggyback in the data packet’s header. While for the position of the destination, we assume that a location registration and lookup service which maps node addresses to locations .When a source node wants to transmit a packet, it getsthe location of the destination first and then attaches it tothe packet header. Due to the destination node’s movement, the multihop path may diverge from the true location of the final destination and a packet would be dropped .To deal with such issue, additional check for the destination node is introduced. At each hop, the node that forwards the packet will check its neighbor list to see whether the destination is within its transmission range. If yes, the packet will be directly forwarded to the destination.

In POR, the MAC multicast mode is used.The packet is transmitted as unicast in IP layer and multiple reception is achieved using MAC interception.The use of RTS/CTS/DATA/ACK significantly reduces the collision and all the nodes within the transmission range of the sender can eavesdrop on the packet successfully with higher probability due to medium reservation.As the data packets are transmitted in a multicast-like form, each of them is identified with a unique tuple (src_ip,seq_no) where src_ip is the IP address of the source node and seq_no is the corresponding sequence number. Every node maintains a monotonically increasing sequence number,and an ID_Cache to record the ID (src_ip, seq_no) of the packets that have been recently received. If a packet with the same ID is received again, it will be discarded. Otherwise, it will be forwarded at once if the receiver is the next hop, or cached in a Packet List if it is received by a forwarding candidate, or dropped if the receiver is not specified. The packet in the Packet List will be sent out after waiting for a certain number of time slots or discarded if the same packet is received again during the waiting period .The basic routing scenario of POR can be simply illustrated in Fig. 1. In normal situation without link break,the packet is forwarded by the next hop node (e.g.,nodes A, E) and the forwarding candidates (e.g., nodes B,C; nodes F, G) will be suppressed by the next hop node’s transmission. In case node A fails to deliver the packet nodeB, the forwarding candidate with the highest priority, will relay the packet and suppress the lower priority candidate’sforwarding (e.g., node C) as well as node S. By using thefeedback from MAC layer, node S will remove node A fromthe neighbor list and select a new next hop node for the subsequent packets. The packets in the interface queuetaking node A as the next hop will be given a second chanceto reroute. For the packet pulled back from the MAC layer,it will not be rerouted as long as node S overhears node B’sforwarding.

Fig. 1. (a) The operation of POR in normal situation. (b) The operation ofPOR when the next hop fails to receive the packet.

2.2 Selection and Prioritization of ForwardingCandidates

. The forwarding area is determined by the sender and the next hop node. A node located in the forwarding area satisfies the following two conditions: 1) it makes positive progress toward the destination; and 2) its distance to the next hop node should not exceed half of the transmission range of a wireless node so that ideally all the forwarding candidates can hear from one another. In Fig. 1, the area enclosed by the bold curve is defined as the forwarding area. The nodes in this area, besides node A (i.e., nodes B, C), are potential candidates. According to the required number of backup nodes, some of them will be selected as forwarding candidates. The priority of a forwarding candidate is decided by its distance to the destination. When a node sends or forwards a packet, it selects the next hop forwarder as well as the forwarding candidates among its neighbors. The next hop and the candidate list comprise the forwarder list. Every node maintains a forwarding table for the packet of each flow that it has sent or forwarded. Before calculating a new forwarder list, it looks up the forwarding table to check if a valid item for that destination is still available. The forwarding table is constructed during data packet transmissions and it maintenance is much easier than a routing table

2.3 Limitation on Possible Duplicate Relaying

Due to collision and nodes’ movement, some forwardingcandidates may fail to receive the packet forwarded by the next hop node or higher priority candidate, so that a certain amount of duplicate relaying would occur.. To limit such duplicate relaying, only the packet that has been forwarded by the source and the next hop node is transmitted in an opportunistic fashion and is allowed to be cached by multiple candidates. In other words, only the source and the next hop node need to calculate the candidate list, while for the packet relayed by a forwarding candidate, the candidate list is empty. In this way, the propagation area of a packet is limited to a certain band between the source and the destination,. With the use of ID cache, duplicate packets will be dropped soon and would not propagate any further.

Fig. 2. Duplicate relaying is limited in the region enclosed by the bold curve

2.4 MAC Modification and Complementary Techniques

2.4.1 MAC Interception

In the network layer, the packet is sent via unicast, to the best node which is elected by greedy forwarding as the next hop. In this way, it provide utilization of the collision avoidance supported by 802.11 MAC. While on the receiver side, we do some modification of theMAC-layer address filter: even when the data packet’s next hop is not the receiver, it is also delivered to the upper layer but with some hint set in the packet header indicating that this packet is overheard. It is then further processed by POR. Hence, the benefit of both broadcast and unicast an be achieved.

2.4.2 MAC Callback

When the MAC layer fails to forward a packet, the function implemented in POR mac_callback will be executed. The item in the forwarding table corresponding to that destination will be deleted and the next hop node in the neighbor list will also be removed. If the transmission of the same packet by a forwarding candidate is overheard, then the packet will be dropped without reforwarding again; otherwise, it will be given a second chance to reroute. The packets with the same next hop in the interface queue which is located between the routing layer and MAC layer will also be pulled back for rerouting. As the location information of the neighbors is updated periodically.

2.4.3 Interface Queue Inspection

One of the key points of POR is that when an intermediate node receives a packet with the same ID it means a better forwarder has already taken over the function. Hence, it will drop that packet from its packet list .Besides maintaining the packet list, we also check the interface queue. We do this because when the packet arrives at the routing layer, the same packet might have already been sent down to the lower layers by the current node. With additional inspection of the interface

3VIRTUAL DESTINATION-BASED VOID HANDLING

In order to enhance the robustness of POR in the network where nodes are not uniformly distributed and large holes may exist, a complementary void handling mechanism based on virtual destination is proposed

..3.1 Trigger Node

In many existing geographic routing protocols, the mode change happens at the void node, e.g., Node B in Fig. 3.Then, Path 1 (A-B-E-) and/or Path 2 (A-B-C-F- ) can be used to route around the communication hole. From Fig. 3, it is obvious that Path 3 (A-C-F-) is better than Path 2. If the mode switch is done at Node A, Path 3 will be tried instead of Path 2 while Path 1 still gets the chance to be used. A message called void warning, which is actually the data packet returned from Node B to Node A with some flag set in the packet header, is introduced to trigger the void handling mode. As soon as the void warning is received, Node A (referred to as trigger node) will switch the packet delivery from greedy mode to void handling mode and rechoose better next hops to forward the packet. Of course, if the void node happens to be the source node, packet forwarding mode will be set as void handling at that node without other choice

Fig. 3. Potential paths around the void

3.2 Virtual Destination

In order to enable opportunistic forwarding in void handling virtual destination is introduced, as the temporary target. Virtual destinations are located at the circumference with the trigger node as center (Fig. 4), but the radius of the circle is set as a value that is large enough They are used to guide the direction of packet delivery during void handling. Compared to the real destination D, a virtual destination has a certain degree of offset .With the help of the virtual destination, the potential forwarding area is significantly extended. Strictly speaking, our mechanism cannot handle all kinds of communication voids, since not all the neighbors of the current node are covered

Fig. 4. Potential forwarding area is extended with virtual destination.

3.3 Switch Back to Greedy Forwarding

A fundamental issue in void handling is when and how to switch back to normal greedy forwarding. From Fig. 4 we can see that the forwarding area in void handling can be divided into two parts: A-I and A-II. To prevent the packet from deviating too far. from the right direction or even missing the chance to switch back to normal greedy forwarding, the candidates in A-I should be preferred and are thus assigned with a higher priority in relaying. Therefore, a scaling parameter is introduced for the candidates located in A-II. The progress toward the virtual destination made by these nodes is multiplied by a coefficient η(0<η<1), called scaling parameter which is set as 0.75 in our experiment. After a packet has been forwarded to route around the communication void for more than two hops (including two hops), the forwarder will check whether there is any potential candidate that is able to switch back. If yes, that node will be selected as the next hop, but the mode is still void handling. Only if the receiver finds that its own location is nearer to the real destination than the void node and it gets at least one neighbor that makes positive progress towards the real destination, it will change the forwarding mode back to normal greedy forwarding.

3.4 Path Acknowledgment and Disrupt Message

In VDVH, if a trigger node finds that there are forwarding candidates in both directions, the data flow will be split into two where the two directions will be tried simultaneously for a possible route around the communication void. In order to reduce unnecessary duplication, two control messages are introduced, namely, path acknowledgment and reverse suppression. If a forwarding candidate receives a packet that is being delivered or has been delivered in void handling mode, it will record a reverse entry. Once the packet reaches the destination, a path acknowledgment will be sent along the reverse path to inform the trigger node. Then, the trigger node will give up trying the other direction. For the same flow, the path acknowledgment will be periodically sent (not on per-packet basis; otherwise,there will be too many control messages). If there is another trigger node upstream, the path acknowledgment will be further delivered to that node, and so on. On the other hand, if a packet that is forwarded in void handling mode cannot go any further or the number of hops traversed exceeds a certain threshold but it is still being delivered in void handling mode, a DISRUPT control packet will be sent back to the trigger node as reverse suppression. Once the trigger node receives the message, it will stop trying that direction.