Abstract-Routing protocols developed for ad hoc wireless networks use broadcast transmission to either discover a route or disseminate information. More specifically, reactive routing protocols has to flood the network with a route request (RREQ) message in order to find an optimal route to the destination. Several applications developed for vehicular ad hoc wireless networks (VANET), which is a subset of MANET, rely on broadcast to propagate useful traffic information to other vehicles located within a certain geographical area. However, the conventional broadcast mechanism may lead to the so-called broadcast storm problem. In this paper, we explore how serious the broadcast storm problem is in both MANET and VANET by examining how broadcast packets propagate in a 2-dimensional open area and on a straight road or highway scenarios. In addition, we propose three novel distributed broadcast suppression techniques; i.e., weighted p-persistence, slotted 1-persistence, and slotted ppersistence schemes. Our simulation results show that the proposed schemes can achieve up to 90% reduction in packet loss rate while keeping the end-to-end delay at acceptable levels for most VANET applications. They can also be used together with the route discovery process to guide the routing protocols to select routes with fewer hop counts. Broadcast transmission is used for at least two very different purposes in MANET. Firstly, many MANET routing protocols broadcasts RREQ messages in order to search for a route to a particular host. In this case, the goal is to propagate the RREQ message to the destination as quickly and efficiently as possible, i.e., RREQ message from the optimal path should be the first one to arrive at the destination. Alternatively, some applications, especially ones that were developed for vehicular ad hoc wireless networks (VANET), may rely on broadcast transmission to disseminate data packet to nodes in a certain geographical area. However, it is well-known that blindly broadcasting the packets may lead to frequent contention, and collisions in transmission among neighboring nodes. This problem is sometimes referred to as the broadcast storm problem. In this paper, we explore how serious the broadcast storm problem is in two very different scenarios; (i) in NIANET where problem rises during the route discovery process, and (ii) in VANET where most applications typically favor broadcast transmissions. While multiple solutions exist to alleviate the broadcast storm problem in a usual MANET environment [1-6], none of these solutions address the problem in the VANET context, nor do they study the impact of broadcast storm on routing decisions. 1-4244-0425-8/06/$20.00 ©2006 IEEE While most studies, to the best of our knowledge, focus on improving the performance in terms of latency, overhead, and network reachability, in this paper, we also consider packet loss ratio, route discovery time, and the number of hops chosen by the routing protocols as our performance metrics. More specifically, we propose three light-weight broadcast techniques; weighted p-persistence, slotted 1-persistence, and slottedp-persistence, which give priority to shortest path route and offer up to 90%0 reduction in packet loss rate while keeping the latency at acceptable levels for most applications and also providing maximum network reachability. The proposed schemes are distributed and rely on GPS and/or received signal strength information, but do not require any other prior knowledge about network topology. The remainder of this paper is organized as follows. Related research are discussed in Section II. The impact of broadcast storm in MANET and VANET is quantified and discussed in detail in Section III. The algorithms proposed for mitigating the broadcast storm are described in detail in Section IV. The performance of the three broadcast techniques are presented in Sections V and VI. Finally, the main findings and contributions of this paper are summarized in Section VII. In the following, we briefly describe related research activities in VANET and other broadcast techniques proposed for general MANETs. Unlike other forms of MANETs, applications developed for VANET have a very specific and clear goal of providing intelligent and safe transport systems. Emergency warning for public safety is one of many applications that is highly time-critical and requires a more intelligent broadcast mechanism than just blind flooding. In [7] , the authors study how broadcast performance scales in VANET and propose a priority based broadcast scheme which gives higher priority to nodes that need to transmit time-critical messages. The proposed algorithm categorizes nodes in the network into multiple classes with different priorities and schedules the packet transmission accordingly. Although this technique is not designed to solve the broadcast storm problem per se, it can indirectly mitigate the severity of the storm by allowing nodes with higher priority to access the channel as quickly as possible.
Authors in REF , have extensively studied the broadcast storm problem in an implementation using IEEE 802.11 and suggested modifications to the draft.
On the Broadcast Storm Problem in Ad hoc Wireless Networks
2006 3rd International Conference on Broadband Communications, Networks and Systems
2006 3rd International Conference on Broadband Communications, Networks and Systems
Computer Science