A survey on probabilistic broadcast schemes for wireless ad hoc networks

Broadcast or flooding is a dissemination technique of paramount importance in wireless ad hoc networks. The broadcast scheme is widely used within routing protocols by a wide range of wireless ad hoc networks such as mobile ad hoc networks, vehicular ad hoc networks, and wireless sensor networks, and used to spread emergency messages in critical scenarios after a disaster scenario and/or an accidents. As the type broadcast scheme used plays an important role in the performance of the network, it has to be selected carefully. Though several types of broadcast schemes have been proposed, probabilistic broadcast schemes have been demonstrated to be suitable schemes for wireless ad hoc networks due to a range of benefits offered by them such as low overhead, balanced energy consumption, and robustness against failures and mobility of nodes. In the last decade, many probabilistic broadcast schemes have been proposed by researchers. In addition to reviewing the main features of the probabilistic schemes found in the literature, we also present a classification of the probabilistic schemes, an exhaustive review of the evaluation methodology including their performance metrics, types of network simulators, their comparisons, and present some examples of real implementations, in this paper

On the performance of probabilistic flooding in wireless mobile ad hoc networks

Broadcasting in MANET’s has traditionally been based on flooding, but this can induce broadcast storms that severely degrade network performance due to redundant retransmission, collision and contention. Probabilistic flooding, where a node rebroadcasts a newly arrived one-to-all packet with some probability, p, was an early suggestion to reduce the broadcast storm problem. The first part of this thesis investigates the effects on the performance of probabilistic flooding of a number of important MANET parameters, including node speed, traffic load and node density. It transpires that these parameters have a critical impact both on reachability and on the number of so-called “saved rebroadcast packets” achieved. For instance, across a range of rebroadcast probability values, as network density increases from 25 to 100 nodes, reachability achieved by probabilistic flooding increases from 85% to 100%. Moreover, as node speed increases from 2 to 20 m/sec, reachability increases from 90% to 100%. The second part of this thesis proposes two new probabilistic algorithms that dynamically adjust the rebroadcasting probability contingent on node distribution using only one-hop neighbourhood information, without requiring any assistance of distance measurements or location-determination devices. The performance of the new algorithm is assessed and compared to blind flooding as well as the fixed probabilistic approach. It is demonstrated that the new algorithms have superior performance characteristics in terms of both reachability and saved rebroadcasts. For instance, the suggested algorithms can improve saved rebroadcasts by up to 70% and 47% compared to blind and fixed probabilistic flooding, respectively, even under conditions of high node mobility and high network density without degrading reachability. The final part of the thesis assesses the impact of probabilistic flooding on the performance of routing protocols in MANETs. Our performance results indicate that using our new probabilistic flooding algorithms during route discovery enables AODV to achieve a higher delivery ratio of data packets while keeping a lower routing overhead compared to using blind and fixed probabilistic flooding. For instance, the packet delivery ratio using our algorithm is improved by up to 19% and 12% compared to using blind and fixed probabilistic flooding, respectively. This performance advantage is achieved with a routing overhead that is lower by up to 28% and 19% than in fixed probabilistic and blind flooding, respectively

Hybrid probabilistic broadcast schemes for mobile ad hoc networks

Broadcasting is one of the fundamental data dissemination mechanisms in mobile ad hoc network (MANET), which is, for instance, extensively used in many routing protocols for route discovery process. The dynamic topology and limited communication bandwidth of such networks pose a number of challenges in designing an efficient broadcasting scheme for MANETs. The simplest approach is flooding, where each node retransmit every unique received packet exactly once on each outgoing link. Although flooding ensures that broadcast packet is received by all network nodes, it generates many redundant transmissions which can trigger high transmission collision and contention in the network, a phenomenon referred to as the broadcast storm. Several probabilistic broadcast algorithms have been proposed that incur low communication overhead to mitigate the broadcast storm problem and tend to show superior adaptability in changing environments when compared to deterministic (i.e., non-probabilistic) schemes. However, most of these schemes reduce redundant broadcasts at the expense of reachability, a requirement for near-global network topological information or support from additional hardware. This research argues that broadcast schemes that combine the important features of fixed probabilistic and counter-based schemes can reduce the broadcast storm problem without sacrificing reachability while still achieving better end-to-end delay. To this end, the first part of this research investigate the effects of forwarding probabilities and counter threshold values on the performance of fixed probabilistic and counter-based schemes. The findings of this investigation are exploited to suggest a new hybrid approach, the Probabilistic Counter-Based Scheme (PCBS) that uses the number of duplicate packets received to estimate neighbourhood density and assign a forwarding probability value to restrict the generation of so many redundant broadcast packets. The simulation results reveal that under various network conditions PCBS reduces the number of redundant transmissions, collision rate and end-to-end delay significantly without sacrificing reachability when compared against counter-based, fixed probabilistic and flood broadcasting. Often in MANETs, there are regions of different node density due to node mobility. As such, PCBS can suffer from a degree of inflexibility in terms of rebroadcast probability, since each node is assigned the same forwarding probability regardless of its local neighbourhood conditions. To address this shortcoming, the second part of this dissertation proposes an Adjusted Probabilistic Counter-Based Scheme (APCBS) that dynamically assigns the forwarding probability to a node based on its local node density using a mathematical function. Thus, a node located in a sparse region of the network is assigned a high forwarding probability while a node located in denser region is assigned a relatively lower forwarding probability. These combined effects enhance end-to-end delay, collision rate and reachability compared to PCBS variant. The performance of most broadcasting schemes that have been suggested for MANETs including those presented here, have been analysed in the context of “pure” broadcast scenarios with relatively little investigation towards their performance impact on specific applications such as route discovery process. The final part of this thesis evaluates the performance of the well-known AODV routing protocol when augmented with APCBS route discovery. Results indicate that the resulting route discovery approach reduces the routing overhead, collision rate and end-to-end delay without degrading the overall network throughput compared to the existing approaches based on flooding, counterbased and fixed probabilistic route discovery

A survey of flooding, gossip routing, and related schemes for wireless multi- hop networks

Flooding is an essential and critical service in computer networks that is used by many routing protocols to send packets from a source to all nodes in the network. As the packets are forwarded once by each receiving node, many copies of the same packet traverse the network which leads to high redundancy and unnecessary usage of the sparse capacity of the transmission medium. Gossip routing is a well-known approach to improve the flooding in wireless multi-hop networks. Each node has a forwarding probability p that is either statically per-configured or determined by information that is available at runtime, e.g, the node degree. When a packet is received, the node selects a random number r. If the number r is below p, the packet is forwarded and otherwise, in the most simple gossip routing protocol, dropped. With this approach the redundancy can be reduced while at the same time the reachability is preserved if the value of the parameter p (and others) is chosen with consideration of the network topology. This technical report gives an overview of the relevant publications in the research domain of gossip routing and gives an insight in the improvements that can be achieved. We discuss the simulation setups and results of gossip routing protocols as well as further improved flooding schemes. The three most important metrics in this application domain are elaborated: reachability, redundancy, and management overhead. The published studies used simulation environments for their research and thus the assumptions, models, and parameters of the simulations are discussed and the feasibility of an application for real world wireless networks are highlighted. Wireless mesh networks based on IEEE 802.11 are the focus of this survey but publications about other network types and technologies are also included. As percolation theory, epidemiological models, and delay tolerant networks are often referred as foundation, inspiration, or application of gossip routing in wireless networks, a brief introduction to each research domain is included and the applicability of the particular models for the gossip routing is discussed

Probabilistic route discovery for Wireless Mobile Ad Hoc Networks (MANETs)

Mobile wireless ad hoc networks (MANETs) have become of increasing interest in view of their promise to extend connectivity beyond traditional fixed infrastructure networks. In MANETs, the task of routing is distributed among network nodes which act as both end points and routers in a wireless multi-hop network environment. To discover a route to a specific destination node, existing on-demand routing protocols employ a broadcast scheme referred to as simple flooding whereby a route request packet (RREQ) originating from a source node is blindly disseminated to the rest of the network nodes. This can lead to excessive redundant retransmissions, causing high channel contention and packet collisions in the network, a phenomenon called a broadcast storm. To reduce the deleterious impact of flooding RREQ packets, a number of route discovery algorithms have been suggested over the past few years based on, for example, location, zoning or clustering. Most such approaches however involve considerably increased complexity requiring additional hardware or the maintenance of complex state information. This research argues that such requirements can be largely alleviated without sacrificing performance gains through the use of probabilistic broadcast methods, where an intermediate node rebroadcasts RREQ packets based on some suitable forwarding probability rather than in the traditional deterministic manner. Although several probabilistic broadcast algorithms have been suggested for MANETs in the past, most of these have focused on “pure” broadcast scenarios with relatively little investigation of the performance impact on specific applications such as route discovery. As a consequence, there has been so far very little study of the performance of probabilistic route discovery applied to the well-established MANET routing protocols. In an effort to fill this gap, the first part of this thesis evaluates the performance of the routing protocols Ad hoc On demand Distance Vector (AODV) and Dynamic Source Routing (DSR) augmented with probabilistic route discovery, taking into account parameters such as network density, traffic density and nodal mobility. The results reveal encouraging benefits in overall routing control overhead but also show that network operating conditions have a critical impact on the optimality of the forwarding probabilities. In most existing probabilistic broadcast algorithms, including the one used here for preliminary investigations, each forwarding node is allowed to rebroadcast a received packet with a fixed forwarding probability regardless of its relative location with respect to the locations of the source and destination pairs. However, in a route discovery operation, if the location of the destination node is known, the dissemination of the RREQ packets can be directed towards this location. Motivated by this, the second part of the research proposes a probabilistic route discovery approach that aims to reduce further the routing overhead by limiting the dissemination of the RREQ packets towards the anticipated location of the destination. This approach combines elements of the fixed probabilistic and flooding-based route discovery approaches. The results indicate that in a relatively dense network, these combined effects can reduce the routing overhead very significantly when compared with that of the fixed probabilistic route discovery. Typically in a MANET there are regions of varying node density. Under such conditions, fixed probabilistic route discovery can suffer from a degree of inflexibility, since every node is assigned the same forwarding probability regardless of local conditions. Ideally, the forwarding probability should be high for a node located in a sparse region of the network while relatively lower for a node located in a denser region of the network. As a result, it can be helpful to identify and categorise mobile nodes in the various regions of the network and appropriately adjust their forwarding probabilities. To this end the research examines probabilistic route discovery methods that dynamically adjust the forwarding probability at a node, based on local node density, which is estimated using number of neighbours as a parameter. Results from this study return significantly superior performance measures compared with fixed probabilistic variants. Although the probabilistic route discovery methods suggested above can significantly reduce the routing control overhead without degrading the overall network throughput, there remains the problem of how to select efficiently forwarding probabilities that will optimize the performance of a broadcast under any given conditions. In an attempt to address this issue, the final part of this thesis proposes and evaluates the feasibility of a node estimating its own forwarding probability dynamically based on locally collected information. The technique examined involves each node piggybacking a list of its 1-hop neighbours in its transmitted RREQ packets. Based on this list, relay nodes can determine the number of neighbours that have been already covered by a broadcast and thus compute the forwarding probabilities most suited to individual circumstances

Enhanced Probabilistic Broadcasting Scheme for Routing in MANETs. An investigation in the design analysis and performance evaluation of an enhanced probabilistic broadcasting scheme for on-demand routing protocols in mobile ad-hoc networks.

Broadcasting is an essential and effective data propagation mechanism with several important applications, such as route discovery, address resolution and many other network services. Though data broadcasting has many advantages, it can also cause a high degree of contention, collision and congestion, leading to what is known as ¿broadcast storm problems¿. Broadcasting has traditionally been based on the flooding protocol, which simply overflows the network with a high number of rebroadcast messages until these reach all the network nodes. A good probabilistic broadcast protocol can achieve high saved rebroadcast (SRB), low collision and a lower number of relays. When a node is in a sparse region of the network, rebroadcasting is relatively more important while the potential redundancy of rebroadcast is low because there are few neighbours which might rebroadcast the packet unnecessarily. Further, in such a situation, contention over the wireless medium resulting from Redundant broadcasts is not as serious as in scenarios with medium or high density node populations. This research proposes a dynamic probabilistic approach that dynamically fine-tunes the rebroadcast probability according to the number of neighbouring nodes distributed in the ad-hoc network for routing request packets (RREQs) without requiring the assistance of distance measurements or location-determination devices. The main goal of this approach is to reduce the number of rebroadcast packets and collisions in the network. The performance of the proposed approach is investigated and compared with simple AODV, fixed-probabilistic and adjusted-probabilistic flooding [1] schemes using the GloMoSim network simulator and a number of important MANET parameters, including node speed, traffic load and node density under a Random Waypoint (RWP) mobility model. Performance results reveal that the proposed approach is able to achieve higher SRB and less collision as well as a lower number of relays than fixed probabilistic, simple AODV and adjusted-probabilistic flooding. In this research, extensive simulation experiments have been conducted in order to study and analyse the proposed dynamic probabilistic approach under different mobility models. The mobility model is designed to describe the movement pattern of mobile customers, and how their position, velocity and acceleration change over time. In this study, a new enhanced dynamic probabilistic flooding scheme is presented. The rebroadcast probability p will be calculated dynamically and the rebroadcasting decision will be based on the average number of nodes in the ad-hoc networks. The performance of the new enhanced algorithm is evaluated and compared to the simple AODV, fixed-probabilistic, adjusted-probabilistic and dynamic-probabilistic flooding schemes. It is demonstrated that the new algorithm has superior performance characteristics in terms of collision, relays and SRB. Finally, the proposed schemes are tested and evaluated through a set of experiments under different mobility models to demonstrate the relative merits and capabilities of these schemes

Encounter gossip: a high coverage broadcast protocol for MANET

PhD ThesisMobile Ad-hoc Networks (MANETs) allow deployment of mobile wireless devices or nodes in a range of environments without any fixed infrastructure and hence at a minimal setup cost. Broadcast support that assures a high coverage (i.e., a large fraction of nodes receiving a broadcast) is essential for hosting user applications, and is also non-trivial to achieve due to the nature of devices and mobility. We propose Encounter Gossip, a novel broadcast protocol, which holds minimal state and is unaware of network topology. Coverage obtained can be made arbitrarily close to 1 at a moderate cost of extra message tra c, even in partition-prone networks. Under certain simplifying assumptions, it is shown that a high coverage is achieved by making a total of O(n ln n) broadcasts, where n is the number of nodes, and the time to propagate a message is O(ln n). The e ect of various network parameters on the protocol performance is examined. We then propose modifications to minimise the number of redundant transmissions without compromising the achieved coverage. Two approaches are pursued: timer based and history based. The e ectiveness of each of these approaches is assessed through an extensive set of simulation experiments in the context of two mobility models. Specifically, we introduce a new heuristic alpha policy which achieves significant reduction in redundancy with negligible reduction in coverage. A generalisation to multiple broadcasts proceeding in parallel is proposed and the protocol is refined to reduce problems that can occur due to the effects of high mobility when transmitting a large number of messages. Finally, we implement and validate Encounter Gossip in the context of a real-life mobile ad-hoc network. All these investigations suggest that the protocol, together with the proposed modifications and re nements, is suited to MANETs of varying degrees of node densities and speeds