Deepti S. Nandiraju

Wireless Mesh Networks: Current Challenges and Future Directions of Web-In-The-Sky

Within the short span of a decade, Wi-Fi hotspots have revolutionized Internet service provisioning. With the increasing popularity and rising demand for more public Wi-Fi hotspots, network service providers are facing a daunting task. Wi-Fi hotspots typically require extensive wired infrastructure to access the backhaul network, which is often expensive and time consuming to provide in such situations. wireless mesh networks (WMNs) offer an easy and economical alternative for providing broadband wireless Internet connectivity and could be called the web-in-the-sky. In place of an underlying wired backbone, a WMN forms a wireless backhaul network, thus obviating the need for extensive cabling. They are based on multihop communication paradigms that dynamically form a connected network. However, multihop wireless communication is severely plagued by many limitations such as low throughput and limited capacity. In this article we point out key challenges that are impeding the rapid progress of this upcoming technology. We systematically examine each layer of the network and discuss the feasibility of some state-of-the-art technologies/protocols for adequately addressing these challenges. We also provide broader and deeper insight to many other issues that are of paramount importance for the successful deployment and wider acceptance of WMNs.

Multipath Routing in Wireless Mesh Networks

Wireless mesh networks are envisioned to support the wired backbone with a wireless backbone for providing Internet connectivity to residential areas and offices. Routing protocols designed for mobile ad hoc networks (MANETs) primarily concentrate on finding a single best possible route to any destination out of the various paths available. However in wireless mesh networks, traffic is primarily routed either towards the Internet gateways (IGWs) or from the IGWs to the access points (APs). Thus, if multiple APs choose the best throughput path towards a gateway, the traffic loads on certain paths and mesh routers increases tremendously thereby deteriorating the overall performance of the network. To this end, we propose a novel multi-path hybrid routing protocol, multipath mesh (MMESH), that effectively discovers multiple paths. We also propose elegant traffic splitting algorithms for balancing traffic over these multiple paths to synergistically improve the overall performance. Through extensive simulations, we observe that our protocol works very well to cope with the variations in the network. Our protocol also improves the performance of flows traversing multiple hops

Achieving Load Balancing in Wireless Mesh Networks Through Multiple Gateways

Wireless mesh networks (WMNs) are evolving to be the key technology of the future. As the WMNs are envisioned to provide high bandwidth broadband service to a large community of users, the Internet gateway (IGW) which acts as a central point of Internet attachment for the mesh routers, it is likely to be a potential bottleneck because of its limited wireless link capacity. We propose a novel technique that elegantly balances the load among the different IGWs in a WMN. We switch the point of attachment of an active source serviced gateway depending on the average queue length at the IGW. The proposed load balancing scheme includes: an initial gateway discovery module, which determines a primary gateway for a mesh router and a load balancing module that rebalances the load among the gateways. We use ns-2 for evaluating our proposed scheme and we observe that the proposed scheme is able to balance the traffic efficiently

A novel queue management mechanism for improving performance of multihop flows in IEEE 802.11s based mesh networks

Wireless mesh networks exploit multi-hop wireless communications between access points to replace wired infrastructure. However, in multi-hop networks, effective bandwidth decreases with increasing number of hops, mainly due to increased spatial contention. Longer hop length flows suffer from extremely low throughputs which is highly undesirable in the envisioned scenarios for mesh networks. In this paper, we show that queue/buffer management, at intermediate relay mesh nodes, plays an important role in limiting the performance of longer hop length flows. We propose a novel queue management algorithm for IEEE 802.11s based mesh networks that improves the performance of multihop flows by fairly sharing the available buffer at each mesh point among all the active source nodes whose flows are being forwarded. Extensive simulations reveal that our proposed scheme substantially improves the performance of multihop flows. We also identify some important design issues that should be considered for the practical deployment of such mesh networks

Adaptive state-based multi-radio multi-channel multi-path routing in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are envisioned to seamlessly extend the network connectivity to end users by forming a wireless backbone that requires minimal infrastructure. Unfortunately for WMNs, frequent link quality fluctuations, excessive load on selective links, congestion, and limited capacity due to the half-duplex nature of radios are some key limiting factors that hinder their deployment. To address these problems, we propose a novel Adaptive State-based Multi-path Routing Protocol (ASMRP), which constructs Directed Acyclic Graphs (DAGs) from each Mesh Router (MR) to Internet Gateways (IGWs) and effectively discovers multiple optimal path set between any given MR-IGW pair. A congestion aware traffic splitting algorithm to balance traffic over these multiple paths is presented which synergistically improves the overall performance of the WMNs. We design a novel Neighbor State Maintenance module that innovatively employs a state machine at each MR to monitor the quality of links connecting its neighbors in order to cope with unreliable wireless links. We also employ a 4-radio architecture for MRs, which allows them to communicate over multiple radios tuned to non-overlapping channels and better utilize the available spectrum. Through extensive simulations using ns-2, we observe that ASMRP substantially improves the achieved throughput (~5 times gain in comparison to AODV), and significantly minimizes end-to-end latencies. We also show that ASMRP ensures fairness in the network under varying traffic load conditions.

Active Cache Based Defense against DoS Attacks in Wireless Mesh Network

Wireless mesh network (WMN) is evolving to be a new paradigm for wireless Internet connectivity as it obviates the need for wired infrastructure at every access point (AP) a.k.a mesh router (MR). The MRs collaboratively forward the traffic towards the Internet gateway (IGW). The self-configurable architecture of MRs paves way for malicious intruders to conduct a denial-of-service attack (DoS) on the MRs by flooding the network with a large volume of traffic; thus rendering the system inaccessible to the real users. In this paper, we present a cache based defense at the MRs to identify flooding style DoS attacks. We use a most frequently used cache mechanism to identify such flows and raise an early alert to curb them. We effectively avert any performance degradation by dropping the identified attack flows along the forwarding routers. Simulation results indicate that our scheme offers an active line of defense against DoS attacks

A Cache Based Traffic Regulator for Improving Performance in WEEE 802.11s based Mesh Networks

Wireless mesh networks (WMNs) are evolving to be the key technology of the future. They aim to provide broadband wireless Internet service to a large community of users by exploiting multi-hop wireless communications between access points thus replacing wired infrastructure. However, in multi-hop networks, flows spanning multiple hops suffer from extremely low throughputs compared to flows traversing fewer hops. In particular, some shorter hop length flows can severely degrade the performance of flows traversing more hops. This is highly undesirable in the envisioned scenarios of mesh networks. In this paper, we propose an elegant most frequently seen cache based traffic regulator that identifies and appropriately regulates the rate of such flows. Extensive simulations reveal that our proposed scheme effectively identifies and controls the traffic from aggressive flows and helps in substantially improving the performance of longer hop length flows

Service Differentiation in IEEE 802.11s Mesh Networks: A Dual Queue Strategy

Wireless Mesh Networks (WMNs) extend the concept of ad hoc multi-hop wireless communication to WLANs in an attempt to complement the wired infrastructure. Unlike in traditional WLANs where all the Access Points (APs) had to be connected to the wired infrastructure, in WMNs, only a subset of APs are connected to the wired infrastructure which cooperatively relay others traffic towards the Internet. Although WMNs are a good proposition for ubiquitous broadband connectivity, they suffer from serious spatial unfairness problem. Often, the proximity of nodes in a network to the main internet attachment plays a significant role in the performance obtained, which is highly undesirable in the envisioned scenario of WMNs. The prime motivation of this paper is to provide fair treatment to all users and provision guaranteed service to users that are attached to a far away AP. We propose a dual queue strategy that provides service guarantees to all users in the network irrespective of their spatial location. The algorithm is designed to elegantly segregate and exclusively reserve queues for either of the traffic. We implement this module above the standard IEEE 802.11 MAC layer thus obviating any modifications to the legacy MAC. Extensive simulations reveal that our proposed scheme substantially improves the performance of multihop flows.