2159703
High Speed Channel Coding Architectures for the Uncoordinated OR Channel
Though it promises high bandwidths, the optical medium is not popular in local area networks. This is because current optical networks do not offer the ease of use and setup that an uncoordinated multiple access network such as Ethernet offers. By careful design and implementation of high speed channel coding architectures, we show that it is possible for optical networks to exhibit these desirable properties while maintaining high optical transmission rates. This paper presents an interleaver-division multiple access (IDMA) architecture implemented with a rate 1/20, 64-state Viterbi decoder and a word-based interleaver. These structures allowed us to achieve optical data rates of 2Gbps in FPGA implementation and 5.4Gbps for 0.18mum ASIC implementation. The techniques presented can be adapted for other similar architectures
15483673
Process Isolation for Reconfigurable Hardware
One of the pillars of trust-worthy computing is process isolation, the ability to keep process data private from other processes running on the same device. While embedded operating systems provide isolation for the software part of these processes, there is no commonly accepted isolation mechanism for the hardware resources. As a result, systems may remain vulnerable to hardware-based attacks. This paper presents a secure coprocessor interface that extends the concept of process isolation into reconfigurable hardware. In the resulting coprocessor design, context information for different processes concurrently accessing the coprocessor is physically kept private. The coprocessor interface can handle context switches between different processes without assistance of the operating system. Because of this, reconfiguration of computation units can occur independent of the main processor. Moreover, it does so with greater efficiency than what is possible using software only.
182657
Key infection: smart trust for smart dust
Future distributed systems may include large self-organizing networks of locally communicating sensor nodes, any small number of which may be subvened by an adversary. Providing security for these sensor networks is important, but the problem is complicated by the fact that managing cryptographic key material is hard: low-cost nodes are neither tamper-proof nor capable of performing public key cryptography efficiently. We show how the key distribution problem can be dealt with in environments with a partially present, passive adversary: a node wishing to communicate securely with other nodes simply generates a symmetric key and sends it in the clear to its neighbours. Despite the apparent insecurity of this primitive, we can use mechanisms for key updating, multipath secrecy amplification and multihop key propagation to build up extremely resilient trust networks where at most a fixed proportion of communications links can be eavesdropped. We discuss applications in which this assumption is sensible. Many systems must perforce cope with principals who are authenticated weakly, if at all; the resulting issues have often been left in the 'too hard' tray. One particular interest of sensor networks is that they present a sufficiently compact and tractable version of this problem. We can perform quantitative analyses and simulations of alternative strategies, some of which we present here. We also hope that This work may start to challenge the common belief that authentication is substantially about bootstrapping trust. We argue that, in distributed systems where the opponent can subvert any small proportion of nodes, it is more economic to invest in resilience than in bootstrapping.
10310314
Sensitivity Analysis in Markov Networks
This paper explores the topic of sensitivity analysis in Markov networks, by tackling questions similar to those arising in the context of Bayesian networks: the tuning of parameters to satisfy query constraints, and the bounding of query changes when perturbing network parameters. Even though the distribution induced by a Markov network corresponds to ratios of multi-linear functions, whereas the distribution induced by a Bayesian network corresponds to multi-linear functions, the results we obtain for Markov networks are as effective computationally as those obtained for Bayesian networks. This similarity is due to the fact that conditional probabilities have the same functional form in both Bayesian and Markov networks, which turns out to be the more influential factor. The major difference we found, however, is in how changes in parameter values should be quantified, as such parameters are interpreted differently in Bayesian networks and Markov networks.
6124330
ACE: An Emergent Algorithm for Highly Uniform Cluster Formation
The efficient subdivision of a sensor network into uniform, mostly non-overlapping clusters of physically close nodes is an important building block in the design of efficient upper layer network functions such as routing, broadcast, data aggregation, and query processing.
15971365
Efficiency of Data Distribution in BitTorrent-Like Systems
BitTorrent (BT) in practice is a very efficient method to share data over a network of clients. In this paper we extend the recent work of Arthur and Panigrahy [1] on modelling the distribution of individual data blocks in BT systems, aiming at a better understanding of why BT can achieve a high degree of parallelism. In particular, we include in our study several new network features that BT systems are using, as well as different local heuristics for routing data blocks in each client. We conduct simulations to figure out to what extent the new network features and routing heuristics would affect the distribution efficiency. Our findings confirm that for the primitive network setting studied in [1], it does require i¾?(blogn) phases for nclients to download bdata blocks. More interestingly, our work suggests that for the more realistic network setting, the heuristics Random and Rarest Block First both allow nclients to download bblocks in b+ O(logn) phases. We believe that the latter bound better reflects the high degree of parallelism of BT observed in reality. It is also worth-mentioning that b+ lognis the smallest possible number of phases needed; it is interesting to see that some simple local routing heuristics have a performance so close to the optimal.
34112863
Compressed Indexes for Approximate String Matching
We revisit the problem of indexing a string S[1..n] to support searching all substrings in S that match a given pattern P[1..m] with at most k errors. Previous solutions either require an index of size exponential in k or need Ω(mk) time for searching. Motivated by the indexing of DNA sequences, we investigate space efficient indexes that occupy only O(n) space. For k = 1, we give an index to support matching in O(m + occ + logn loglogn) time. The previously best solution achieving this time complexity requires an index of size O(n logn). This new index can be used to improve existing indexes for k ≥2 errors. Among others, it can support matching with k=2 errors in O(m logn loglogn + occ) time.