Efficient size estimation and impossibility of termination in uniform dense population protocols

We study uniform population protocols: networks of anonymous agents whose pairwise interactions are chosen at random, where each agent uses an identical transition algorithm that does not depend on the population size $n$. Many existing polylog$(n)$ time protocols for leader election and majority computation are nonuniform: to operate correctly, they require all agents to be initialized with an approximate estimate of $n$ (specifically, the exact value $\lfloor \log n \rfloor$). Our first main result is a uniform protocol for calculating $\log(n) \pm O(1)$ with high probability in $O(\log^2 n)$ time and $O(\log^4 n)$ states ($O(\log \log n)$ bits of memory). The protocol is converging but not terminating: it does not signal when the estimate is close to the true value of $\log n$. If it could be made terminating, this would allow composition with protocols, such as those for leader election or majority, that require a size estimate initially, to make them uniform (though with a small probability of failure). We do show how our main protocol can be indirectly composed with others in a simple and elegant way, based on the leaderless phase clock, demonstrating that those protocols can in fact be made uniform. However, our second main result implies that the protocol cannot be made terminating, a consequence of a much stronger result: a uniform protocol for any task requiring more than constant time cannot be terminating even with probability bounded above 0, if infinitely many initial configurations are dense: any state present initially occupies $\Omega(n)$ agents. (In particular, no leader is allowed.) Crucially, the result holds no matter the memory or time permitted. Finally, we show that with an initial leader, our size-estimation protocol can be made terminating with high probability, with the same asymptotic time and space bounds.Comment: Using leaderless phase cloc

Message Complexity of Population Protocols

The standard population protocol model assumes that when two agents interact, each observes the entire state of the other agent. We initiate the study of $\textit{message complexity}$ for population protocols, where the state of an agent is divided into an externally-visible $\textit{message}$ and an internal component, where only the message can be observed by the other agent in an interaction. We consider the case of $O(1)$ message complexity. When time is unrestricted, we obtain an exact characterization of the stably computable predicates based on the number of internal states $s(n)$: If $s(n) = o(n)$ then the protocol computes semilinear predicates (unlike the original model, which can compute non-semilinear predicates with $s(n) = O(\log n)$), and otherwise it computes a predicate decidable by a nondeterministic $O(n \log s(n))$-space-bounded Turing machine. We then introduce novel $O(\mathrm{polylog}(n))$ expected time protocols for junta/leader election and general purpose broadcast correct with high probability, and approximate and exact population size counting correct with probability 1. Finally, we show that the main constraint on the power of bounded-message-size protocols is the size of the internal states: with unbounded internal states, any computable function can be computed with probability 1 in the limit by a protocol that uses only $\textit{1-bit}$ messages

Stature Estimation from the Right External Ear of Undergraduate Students in South-East Nigeria

Background: Ethnicity, stature and gender influence the anthropometric characteristics of the right ear, thus creating variations which are helpful for sex identification and medico-legal purposes in forensic examinations. This study has produced anthropometric data on the right external ear among the Ikwo people in southeastern Nigeria. Materials and Methods: Ear and lobular indices were obtained from the dimensions of the right external ear of 240 Ikwo adults aged 18-35. Also, three predictive models (equations) were produced in the study. Results: Descriptions of the right external ear for the study population were obtained. Aside from ear indices, which were higher in females than in males, males were taller in stature than females (P<0.001). Regarding correlation, right ear parameters in both sexes appeared positive and strongly correlated with stature. Regression models strongly predicted stature based on external ear measurements. Conclusion: Medical applications (monitoring diseases, forensics, industrial design and apparel design) of this study cannot be overemphasized in this world of medical sciences, in particular when it comes to understand the human external ear in terms of hearing and communication. (Obaje SG, Nwankwo SC, Egwu AO. Stature Estimation from the Right External Ear of Undergraduate Students in South-East Nigeria. SEEMEDJ 2020; 4(2); 12-19

Distributed Systems and Mobile Computing

The book is about Distributed Systems and Mobile Computing. This is a branch of Computer Science devoted to the study of systems whose components are in different physical locations and have limited communication capabilities. Such components may be static, often organized in a network, or may be able to move in a discrete or continuous environment. The theoretical study of such systems has applications ranging from swarms of mobile robots (e.g., drones) to sensor networks, autonomous intelligent vehicles, the Internet of Things, and crawlers on the Web. The book includes five articles. Two of them are about networks: the first one studies the formation of networks by agents that interact randomly and have the ability to form connections; the second one is a study of clustering models and algorithms. The three remaining articles are concerned with autonomous mobile robots operating in continuous space. One article studies the classical gathering problem, where all robots have to reach a common location, and proposes a fast algorithm for robots that are endowed with a compass but have limited visibility. The last two articles deal with the evacuations problem, where two robots have to locate an exit point and evacuate a region in the shortest possible time

Composable computation in discrete chemical reaction networks

We study the composability of discrete chemical reaction networks (CRNs) that stably compute (i.e., with probability 0 of error) integer-valued functions $f:\mathbb{N}^d\to\mathbb{N}$. We consider output-oblivious CRNs in which the output species is never a reactant (input) to any reaction. The class of output-oblivious CRNs is fundamental, appearing in earlier studies of CRN computation, because it is precisely the class of CRNs that can be composed by simply renaming the output of the upstream CRN to match the input of the downstream CRN. Our main theorem precisely characterizes the functions $f$ stably computable by output-oblivious CRNs with an initial leader. The key necessary condition is that for sufficiently large inputs, $f$ is the minimum of a finite number of nondecreasing quilt-affine functions. (An affine function is linear with a constant offset; a quilt-affine function is linear with a periodic offset)

Terminating Distributed Construction of Shapes and Patterns in a Fair Solution of Automata

In this work, we consider a solution of automata (or nodes) that move passively in a well-mixed solution without being capable of controlling their movement. Nodes can cooperate by interacting in pairs and every such interaction may result in an update of their local states. Additionally, the nodes may also choose to connect to each other in order to start forming some required structure. Such nodes can be thought of as small programmable pieces of matter, like tiny nanorobots or programmable molecules. The model that we introduce here is a more applied version of network constructors, imposing physical (or geometric) constraints on the connections that the nodes are allowed to form. Each node can connect to other nodes only via a very limited number of local ports. Connections are always made at unit distance and are perpendicular to connections of neighboring ports, which makes the model capable of forming 2D or 3D shapes. We provide direct constructors for some basic shape construction problems, like spanning line, spanning square, and self-replication. We then develop new techniques for determining the computational and constructive capabilities of our model. One of the main novelties of our approach is that of exploiting the assumptions that the system is well-mixed and has a unique leader, in order to give terminating protocols that are correct with high probability. This allows us to develop terminating subroutines that can be sequentially composed to form larger modular protocols. One of our main results is a terminating protocol counting the size n of the system with high probability. We then use this protocol as a subroutine in order to develop our universal constructors, establishing that it is possible for the nodes to become self-organized with high probability into arbitrarily complex shapes while still detecting termination of the construction

LIPIcs, Volume 251, ITCS 2023, Complete Volume

LIPIcs, Volume 251, ITCS 2023, Complete Volum

Topics in access, storage, and sensor networks

In the first part of this dissertation, Data Over Cable Service Interface Specification (DOCSIS) and IEEE 802.3ah Ethernet Passive Optical Network (ETON), two access networking standards, are studied. We study the impact of two parameters of the DOCSIS protocol and derive the probability of message collision in the 802.3ah device discovery scheme. We survey existing bandwidth allocation schemes for EPONs, derive the average grant size in one such scheme, and study the performance of the shortest-job-first heuristic. In the second part of this dissertation, we study networks of mobile sensors. We make progress towards an architecture for disconnected collections of mobile sensors. We propose a new design abstraction called tours which facilitates the combination of mobility and communication into a single design primitive and enables the system of sensors to reorganize into desirable topologies alter failures. We also initiate a study of computation in mobile sensor networks. We study the relationship between two distributed computational models of mobile sensor networks: population protocols and self-similar functions. We define the notion of a self-similar predicate and show when it is computable by a population protocol. Transition graphs of population protocols lead its to the consideration of graph powers. We consider the direct product of graphs and its new variant which we call the lexicographic direct product (or the clique product). We show that invariants concerning transposable walks in direct graph powers and transposable independent sets in graph families generated by the lexicographic direct product are uncomputable. The last part of this dissertation makes contributions to the area of storage systems. We propose a sequential access detect ion and prefetching scheme and a dynamic cache sizing scheme for large storage systems. We evaluate the cache sizing scheme theoretically and through simulations. We compute the expected hit ratio of our and competing schemes and bound the expected size of our dynamic cache sufficient to obtain an optimal hit ratio. We also develop a stand-alone simulator for studying our proposed scheme and integrate it with an empirically validated disk simulator