Power Aware Routing in Mobile Ad Hoc Networks

We study an on-line broadcast scheduling problem in which requests have deadlines, and the objective is to maximize the weighted throughput, i.e., the weighted total length of the satisfied requests. For the case where all requested pages have the same length, we present an online deterministic algorithm named BAR and prove that it is 4.56-competitive. This improves the previous algorithm of Kim and Chwa [11] which is shown to be 5-competitive by Chan et al. [4]. In the case that pages may have different lengths, we prove a lower bound of Ω(Δ/logΔ) on the competitive ratio where Δ is the ratio of maximum to minimum page lengths. This improves upon the previous $\sqrt{\Delta}$ lower bound in [11,4] and is much closer to the current upper bound of ($\Delta+2\sqrt{\Delta}+2$) in [7]. Furthermore, for small values of Δ we give better lower bounds.

Improved on-line broadcast scheduling with deadlines

With the increasing popularity of portable wireless computers, mechanisms to efficiently transmit information to wireless clients are of significant interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. In such environments, often it is not possible (or not desirable) for the clients to send explicit requests to the server. It has been proposed that in such systems the server should broadcast the data periodically. One challenge in implementing this solution is to determine the schedule for broadcasting the data, such that the wait encountered by the clients is minimized. A broadcast schedule determines what is broadcast by the server and when. In this paper, we present algorithms for determining broadcast schedules that minimize the wait time. Broadcast scheduling algorithms for environments subject to errors, and systems where different clients may listen to different number of broadcast channels are also considered. Performance evaluation results are presented to demonstrate that our algorithms perform well.

http://delab.csd.auth.gr/~dimitris/courses/mpc_fall05/papers/broadcast_scheduling/MUST_BE_READ_ACM_WINET_99_vol5_no3_scheduling_broadcasts_b.pdf

Scheduling data broadcast in asymmetric communication environments

Due to the broadcast nature of radio transmissions, communications in mobile ad hoc networks (MANETs) are more susceptible to malicious traffic analysis. In this paper we propose a novel anonymous on-demand routing protocol, termed MASK, to enable anonymous communications thereby thwarting possible traffic analysis attacks. Based on a new cryptographic concept called pairing, we first propose an anonymous neighborhood authentication protocol which allows neighboring nodes to authenticate each other without revealing their identities. Then utilizing the secret pairwise link identifiers and keys established between neighbors during the neighborhood authentication process, MASK fulfills the routing and packet forwarding tasks nicely without disclosing the identities of participating nodes under a rather strong adversarial model. MASK provides the desirable sender and receiver anonymity, as well as the relationship anonymity of the sender and receiver. It is also resistant to a wide range of adversarial attacks. Moreover, MASK preserves the routing efficiency in contrast to previous proposals. Detailed anonymity analysis and simulation studies are carried out to validate and justify the effectiveness of MASK.

Anonymous communications in mobile ad hoc networks

The shared wireless medium of mobile ad hoc networks facilitates passive, adversarial eavesdropping on data communications whereby adversaries can launch various devastating attacks on the target network. To thwart passive eavesdropping and the resulting attacks, we propose a novel anonymous on-demand routing protocol, termed MASK, which can accomplish both MAC-layer and network-layer communications without disclosing real IDs of the participating nodes under a rather strong adversary model. MASK offers the anonymity of senders, receivers, and sender-receiver relationships in addition to node unlocatability and untrackability and end-to-end flow untraceability. It is also resistant to a wide range of attacks. Moreover, MASK preserves the high routing efficiency as compared to previous proposals. Detailed simulation studies have shown that MASK is highly effective and efficient

/pdf/mask-anonymous-on-demand-routing-in-mobile-ad-hoc-networks-4iop0mh2ef.pdf

MASK: anonymous on-demand routing in mobile ad hoc networks

Broadcasting is an effective way of delivering data to a large population.’ In the broadcast environment under consideration, a server broadcasts data items to all clients simultaneously, according to a certain transmission schedule. Users with pending data requests need to listen to the broadcast channel until their requests are satisfied by the transmitted data. Past research on broadcast scheduling assumes that once a user starts to wait for some data item, the user waits until the desired data item is transmitted by the server. This is often not true in practice. For various reasons, users may lose patience after waiting “too long” and leave with their requests unserved. In this paper, we study the broadcast scheduling problem taking user impatience into account. Based on our analytical results, we propose a scheduling algorithm that can produce a broadcast schedule with high service ratio (i.e., percentage of requests served) as well as low mean waiting time for the requests. Performance evaluation results based on simulations are provided.

Scheduling data broadcast to “impatient” users

Data broadcast has been suggested as a promising method of information dissemination [2,33]. In such an environment, the information server cannot afford to serve the requests from a large population of users individually. Instead, the server uses a broadcast channel to deliver information to all users. A single transmission of a data item satisfies all pending requests for that item. The response time of a request depends on the broadcast time of the desired data item, which is scheduled by the server according to the overall demands for various data items. Therefore, the response time may vary in a large range. We argue that, in addition to mean response time, the variance of response time should also be taken into account by the broadcast scheduler. In this paper, we address the issue of variance optimization in regard to response time. Building on our previous research on mean response time optimization, we propose an algorithm which can minimize the variance of response time. Furthermore, we evaluate an algorithm that facilitates a tradeoff between the mean and variance of response time. Numerical examples that illustrate the performance of our algorithms are also presented.

http://delab.csd.auth.gr/~dimitris/courses/mpc_fall05/papers/broadcast_scheduling/ACM_MONET_02_response_time_broadcast_mean_avg_variance.pdf

Response time in data broadcast systems: mean, variance and tradeoff

Providing anonymous connection service in mobile ad hoc networks is a challenging task. In addition to security concerns, performance concerns must be addressed properly as well. Chaum's mix method (Comms. of the ACM, vol.24(2), p.84-88, 1981) can effectively thwart an adversary's attempt at tracing packet routes and can hide the source and/or destination of packets. However, applying the mix method in ad hoc networks may cause significant performance degradation due to its non-adaptive mix route selection algorithm. We propose a dynamic mix routing algorithm to find topology-dependent mix routes for anonymous connections. Its effectiveness in improving network performance is validated by simulation results. We also address the potential degradation of anonymity due to dynamic mix routing.

/pdf/a-mix-route-algorithm-for-mix-net-in-wireless-mobile-ad-hoc-1dyw1joes3.pdf

A mix route algorithm for mix-net in wireless mobile ad hoc networks

Data broadcast has been suggested as a promising method of information dissemination in the communication environment with assymetric characteristic. In such an environment, the information server cannot afford to serve the requests from a large population of users individually. Instead, the server uses a broadcast channel to deliver information to all users. A single transmission of a data item will satisfy all pending requests for that item. However, the quality of service experienced by a single user turns out to be unpredictable and unstable. The response time of a request depends on the broadcast of the desired data item, which is scheduled by the server according to the overall demands for various data items. Therefore, the response time may vary in a large range, which may hinder a user subscribing to this service. We argue that, in addition to mean response time, the variance of response time should also be taken into account by the broadcast scheduler. In this paper, we address the issue of variance optimization in regard to response time. Building on our previous research on mean response time optimization, we propose an algorithm which can minimize the variance of response time. Furthermore, we evaluate an algorithm that facilitates a trade-off between the mean and variance of response time. Numerical examples that illustrate the performances of our algorithms are also presented.

Scheduling Algorithms for a Data Broadcast System: Minimizing Variance of the Response Time

Traffic analysis poses a serious threat to communication security, especially in wireless networks. Encryption may be used to hide message contents, whereas traffic padding may be used to hide the traffic pattern. This paper deals with the issue of preventing traffic analysis by inserting dummy (or padding) traffic to hide the real traffic pattern. The observable traffic pattern, after dummy traffic has been inserted, is referred to as a cover mode. Since the dummy traffic incurs an overhead, it is important to minimize dummy traffic while achieving the desired security objective. In this paper, we attempt to develop a suitable cover mode with the objective of minimizing energy of preventing traffic analysis by inserting dummy (or padding) traffic to hide the real traffic pattern. The observable traffic pattern, after dummy traffic has been inserted, is referred to as a cover mode. Since the dummy traffic incurs an overhead, it is important to minimize dummy traffic while achieving the desired security objective. In this paper, we attempt to develop a suitable cover mode with the objective of minimizing energy consumption -- the nodes in wireless ad hoc networks typically have limited battery supply, therefore, it is important to minimize the energy consumption. We propose different methods for implementing the cover mode, and evaluate the impact of these techniques on system lifetime and on energy consumption per unit of real traffic transmitted in the network.

Shu Jiang

Papers

Scheduling data broadcast to “impatient” users

Response time in data broadcast systems: mean, variance and tradeoff

A mix route algorithm for mix-net in wireless mobile ad hoc networks

Scheduling Algorithms for a Data Broadcast System: Minimizing Variance of the Response Time

Power-Aware Traffic Cover Mode to Prevent Traffic Analysis in Wireless Ad Hoc Networks