Anindo Mukherjee

Airtime Fairness for IEEE 802.11 Multirate Networks

Under a multirate network scenario, the IEEE 802.11 DCF MAC fails to provide airtime fairness for all competing stations since the protocol is designed for ensuring max-min throughput fairness. As such, the maximum achievable throughput by any station gets bounded by the slowest transmitting peer. In this paper, we present an analytical model to study the delay and throughput characteristics of such networks so that the rate anomaly problem of IEEE DCF multirate networks could be mitigated. We call our proposal time fair CSMA (TFCSMA) which utilizes an interesting baseline property for estimating a target throughput for each competing station so that its minimum contention window could be adjusted in a distributed manner. As opposed to the previous work in this area, TFCSMA is ideally suited for practical scenarios where stations frequently adapt their data rates to changing channel conditions. In addition, TFCSMA also accounts for packet errors due to the time varying properties of the wireless channel. We thoroughly compare the performance of our proposed protocol with IEEE 802.11 and other existing protocols under different network scenarios and traffic conditions. Our comprehensive simulations validate the efficacy of our method toward providing high throughput and time fair channel allocation.

Decentralized key generation scheme for cellular-based heterogeneous wireless ad hoc networks

With the support of cellular system a cellular-based mobile ad hoc network (MANET) offers promising communication scenarios while entails secure data exchange as other wireless systems. In this paper, we propose a novel decentralized key generation mechanism using shared symmetric polynomials in which the base stations (BSs) carry out an initial key generation by a symmetric polynomial in a distributed manner and then pass on the key material to mobile stations (MSs). Thereafter, our proposed key generation scheme enables each pair of MSs to establish a pairwise key without any intervention from the BS, thus reducing the management cost for the BS. The shared key between two MSs is computed without any interaction between them. In addition, the trust among MSs is derived from the cellular infrastructure, thus enjoying an equal security level as provided in the underlying cellular network. Simulations are done to observe the system performance and the results are very encouraging.

Distributed key management for dynamic groups in MANETs

Most existing solutions to group security in Mobile Ad Hoc Networks (MANETs) rely on a multicast Core Based Tree (CBT) for key distribution. Such solutions, although suitable for systems with low mobility and static characteristics, are unsuitable for dynamic and sparse groups with changing neighborhoods. In this paper, we propose an entirely decentralized key generation mechanism, employing a central trusted entity only during initialization. Using our approach, keys can be established between group members with absolutely no prior communication. The solution relies on threshold cryptography and introduces a novel concept of Node-Group-Key (NGK) mapping. We have provided an extensive analytical model for the computations involved and communication costs and have also provided a lie detection mechanism. Simulation results show appreciable performance improvement and enhanced robustness.

Minimizing re-authentication overheads in infrastructure IEEE 802.11 WLAN networks [re-authentication read pre-authentication]

Authentication delays of the order of 1 s are a severe bottleneck in maintaining QoS guarantees over WLANs. Pre-authentication schemes have been proposed to reduce these delays. However, most of these schemes suffer from an increased message overhead on the network. The primary reason for this is that mobility modeling is not on a per-user basis. We exploit the notion of predictability in user mobility patterns and propose a set of novel proactive key distribution algorithms to achieve low latencies while minimising the message overhead in the network. We further provide a model to measure the responsiveness of our schemes to randomness in user motion. Simulation results indicate up to 60% message reduction in comparison to existing schemes, while maintaining similar latency values.

Performance analysis of IEEE 802.11 for multi-hop infrastructure networks

Recent interest in multi-hop infrastructure networks (MINs) has resulted in a need for an accurate model to predict the behavior of such systems. We consider a traffic-based network model to characterize these networks. We first analyze the link delay characteristics of MINs. This is followed by a method to obtain the cdf of multi-hop traffic inter-arrival time. Finally, the IEEE 802.11 distributed coordination function (DCF) is modeled for MINs and expressions for the throughput and delay are obtained. The proposed model is generic and can be used to characterize any MIN for known topology and traffic patterns. We confirm our results through simulations carried out using ns-2

A Perceptron Based Classifier for Detecting Malicious Route Floods in Wireless Mesh Networks

Wireless mesh networks (WMN) are evolving as a new paradigm for broadband Internet, in which a group of static mesh routers employ multihop forwarding to provide wireless Internet connectivity. All routing protocols in WMNs naively assume nodes to be non- malicious. But, the plug-in-and-play architecture of WMNs paves way for malicious users who could exploit some loopholes of the underlying routing protocol. A malicious node can inundate the network by conducting frequent route discovery which severely reduces the network throughput. In this paper, we investigate the detection of route floods by incorporating a machine learning technique. We use a perceptron training model as a tool for intrusion detection. We train the perceptron model by feeding various network statistics and then use it as a classifier. We illustrate using an experimental wireless network (ns-2) that the proposed scheme can accurately detect route misbehaviors with a very low false positive rate.

Exploiting Mobility Patterns to Reduce Re-Authentication Overheads in Infrastructure WLAN Networks

The current EAP-TLS standard accounts for authentication delays of the order of one second for infrastructure 802.11 networks. This delay is clearly unacceptable for maintaining the QoS requirements for a mobile station which have frequent handoffs to different regions. Pre-authentication schemes have been proposed to reduce these delays. However, most of these schemes suffer from an increased network message overhead since they fail to appropriately model the mobility of each individual user. In this paper, we exploit the notion of predictability in user mobility patterns and propose a set of novel proactive key distribution algorithms to achieve low latencies while minimizing the message overhead. Our schemes involve pre-distributing keys in fewer necessary access points (APs) as opposed to all neighboring APs. We evaluate the performance of our schemes for three different mobility models; (i) predictable motion (ii) changing predictable motion and (iii) random motion. Almost under all scenarios, our schemes indicate up to 70% message reduction, while maintaining similar latencies

Analytical Modeling of the Link Delay Characteristics for IEEE 802.11 DCF Multi-Rate WLANs

Performance evaluation of IEEE 802.11 DCF has been widely studied under the assumption of a single transmission rate by all competing nodes. In practice, however, stations typically use different transmission rates. This is done to match to the changing channel conditions. Stations with poor channel conditions typically employ lower transmit rates in comparison to stations with better channel conditions. Under such scenarios, the throughput of each station becomes independent of its own transmit rate; rather it gets bounded by the slowest transmitting peer. This has been popularly classified as the performance anomaly problem. This paper provides a simple yet accurate analytical framework to study the link delay characteristics of such multi-rate networks

Totally distributed key management for dynamic groups in MANETs

Most existing solutions to group security in mobile ad hoc networks (MANETs) rely on a multicast core based tree (CBT) for key distribution. Such solutions, although suitable for systems with low mobility and static characteristics, are highly unsuitable for dynamic and sparse groups with changing neighborhoods. Also, tree based solutions are prone to a man-in-the-middle attack which might lead to network partitioning. Moreover, a group controller is required to control the key generation process. In this paper, we propose an entirely decentralized key generation mechanism. Using our approach, keys can be established between group members with absolutely no prior communication, as long as the group members are known. The solution relies on threshold cryptography and introduces a novel concept of node-group-key (NGK) mapping. Analytical and simulation results show appreciable performance enhancements.

Distributed Pairwise Key Generation Using Shared Polynomials for Wireless Ad Hoc Networks

The infrastructure-less property of wireless ad hoc network makes the traditional central server based security management schemes unsuitable and requires the use of a distributed key management mechanism. In this paper, we propose a distributed pairwise key establishment scheme based on the concept of bivariate polynomials. In our method, any mobile node in an ad hoc network can securely communicate with other nodes just by knowing their corresponding IDs. The bivariate polynomials are shared in such a manner that the shares depend on the coefficient matrix of the polynomial, the requesting node’s ID and the ID of the nodes that respond to the request. We study the behavior of our scheme through simulations and show that our scheme compares well with other schemes and has a much better performance when averaged over the lifetime of the network.