Showing papers in "Computer Networks and Isdn Systems in 2020"

A Revised Gomory-Hu Algorithm Taking Account of Physical Unavailability of Network Channels

Abstract: The classical Gomory-Hu algorithm aims for finding, for given input flows, a network topology for data transmission and bandwidth of its channels which are optimized subject to minimal bandwidth criteria In practice, it may occur that some channels between nodes of the network are not active Ignoring such channels using the topology obtained be the Gomory-Hu algorithm will not lead to an optimal flow-rate

Performance Evaluations of a Cloud Computing Physical Machine with Task Reneging and Task Resubmission (Feedback)

Abstract: Cloud service providers (CSP) provide on-demand cloud computing services, reduces the cost of setting-up and scaling-up IT infrastructure and services, and stimulates shorter establishment times for start-ups that offer or use cloud-based services Task reneging or dropping sometimes occur when a task waits in the queue longer than its timeout or execution deadline, or it is compromised and must be dropped from the queue or as an active queue management strategy to avoid tail dropping of tasks when the queues are full Reneged or dropped tasks could be resubmitted provided they were not dropped due to security reasons In this paper, we present a simple M/M/c/N queueing model of a cloud computing physical machine, where the interarrival times and the services times are exponentially distributed, with N buffer size and c virtual machines running in parallel We present numerical examples to illustrate the effect of task reneging and task resubmission on the queueing delay, probability of task rejection, and the probability of immediate service

On Comparison of Multiserver Systems with Exponential-Pareto Mixture Distribution

Abstract: Mixture models arise when at least two different distributions of data sets are presented In this paper, we introduce the upper and lower bounds for the steady-state performance of a multiserver model of the network node, with Exponential-Pareto mixture distribution of service times We use the failure rate and stochastic comparison techniques together with coupling of random variables to establish some monotonicity properties of the model These theoretical results are illustrated by numerical simulation of GI/G/N queueing systems

Reliability Enhancement of URLLC Traffic in 5G Cellular Networks

Abstract: 5G cellular networks must be able to deliver a small data payload in a very short time (up to 1 ms) with ultra-high probability of success (99.999%) to the mobile user. Achieving ultra-reliable and low-latency communication (URLLC) represents one of the major challenges in terms of system design. This paper covers definitions of latency and the reliability of URLLC traffic. Furthermore, it presents a method for reliability enhancement of URLLC traffic. To this end, the problem of reliability enhancement is formulated as an optimisation problem, the objective of which is to maximise the sum of data rates for all users with the URLLC constraints. Simulation results show that the suggested method validates the proposed model.

Development of High Performance Computing Systems

Abstract: The aim of the work is to present the development trends of high performance computers The analysis focused on system architecture, processors and computing accelerators used Particular attention was paid to interconnection networks, connecting system nodes The problem of energy saving in the construction of large systems was also discussed The data from the list of 500 largest computer systems was used in the analysis

Unreliable Single-Server Queueing System with Customers of Random Capacity

Abstract: In the paper, we investigate one-server queueing system with stationary Poisson arrival process, non-homogeneous customers and unreliable server. As non-homogenity, we mean that each customer is characterized by some arbitrarily distributed random capacity that is called customer volume. Service time of a customer generally depends on his volume. The server can be broken when it is free or busy and the renewal period goes on for random time having an arbitrary distribution. During this period, customers present in the system and arriving to it are not served. Their service continues immediately after renewal period termination. For such systems, we determine the distribution of total volume of customers present in it. An analysis of some special cases and some numerical examples are attached as well.

Minimising the Churn Out of the Service by Using a Fairness Mechanism

Abstract: The paper proposes an algorithm of bandwidth distribution, ensuring fairness to end-users in computer networks The proposed algorithm divides users into satisfied and unsatisfied users It provides fairness in terms of quality of experience (QoE) for satisfied users and quality of service (QoS) for unsatisfied users In this paper, we present detailed comparisons relevant to service providers to show the advantages of the proposed algorithm over the popular max-min algorithm Our algorithm is designed to provide service providers with a mechanism to minimize the number of end-user terminations of service, which is one of the most desired factors for service providers

Detection Efficiency Improvement in Multi–component Anti-spam Systems

Abstract: Multi–layer spam detection systems frequently used in many SMTP servers often suffer from a lack of mutual communication between individual layers. The paper presents the construction of a feedback interconnection between two significant layers, namely Message contents check and Greylisting. The verification in a real SMTP server is performed, demonstrating considerable improvement of spam detection efficiency comparing the previous period with missing interconnection, while for a short testing period. Despite the limited generalizability of the result, it suggests the easy way how spam detection can be improved.

Quantum Router for Qutrit Networks

Abstract: Networks of quantum circuits or, more generally, networks transmitting quantum information will need, just like classical networks (eg internet), a mechanism for directing data to adequate nodes Routing, understood as packet switching, is one of the most important processes in classical networks The issue of routing is also present in quantum networks and an appropriate construction of a quantum router is required to transfer data to specific points in the network We describe an implementation of a router for qutrits in this chapter The router is four-qutrit quantum circuit (with one controlling unit) The efficiency and the accuracy of router’s work is tested by the Fidelity measure The circuit’s dynamics is expressed by a Hamiltonian where the role of generalized Pauli operators is played by the Gell-Mann operators

Analysis of the Block Segmentation Method of the Licklider Transmission Protocol

Abstract: Space communications are continuously challenged by extreme conditions that include large propagation delays, intermittent connectivity, and random losses. To combat these problems, the Licklider Transmission Protocol (LTP) splits data blocks into small segments that are radiated independently and retransmitted as needed, through a process that can be paused during long link disruptions. Given the extreme delays involved, the end performance of this protocol is driven by the number of transmission rounds needed to successfully deliver each block. LTP links are defined as overlays with one or more physical channels in the underlay, therefore with sections that may be on different administrative domains and experiencing different conditions. The question of how to select the length of the segments has received negligible attention and the use of improper values can easily lead to suboptimal performance. The segmentation process used by LTP is examined in this paper to determine the role that segmentation parameters and the conditions of the underlay have on the block delivery times. This goal is achieved through the definition of a basic model of LTP’s transmission process that allows deriving the optimal segmentation parameter. Simulation results provide additional evidence of LTP’s performance contrasting the results of the optimal segment length with fixed-length segments. The results provide a theoretical performance reference for practical parameter optimization methods.

Detection of NAT64/DNS64 by SRV Records: Detection Using Global DNS Tree in the World Beyond Plain-Text DNS

Abstract: Since it has been introduced the NAT64/DNS64 transition mechanism has reputation of method which simply works. This could change as currently used detection method, RFC7050 [16], for this transition mechanism doesn’t work with third party/foreign DNS resolvers. These resolvers have been lately introduced by Mozilla Firefox [1] with implementation of DNS over HTTPS. This paper describes problems connected with default usage of third party DNS resolvers and provides a way how to solve issues of RFC7050 [16] with and without third party resolvers.

Reliability Analysis of a Multipath Transport System in Fog Computing

Abstract: We consider a fog computing approach with function virtualization in an IoT scenario that uses an SDN/NFV protocol stack and multipath communication between its clients and servers at the transport and session layers. We analyze the reliability of the associated redundant transport system comprising two logical channels that are susceptible to random failures. We model the error-prone system with a single repair unit and independent phase-type distributed repair times by a Marshall-Olkin failure model. The failure processes of both channels are described by general Markov-modulated Poisson processes (MMPPs) that are associated with the corresponding failure times and that are driven by the transitions of a common random environment. First we identify the generator matrix of the associated continuous-time Markov chain that is determined by the interarrival times of the Markov-modulated failure processes and the independent phase-type distributed repair times and the Kronecker-product structures of their associated parameter matrices. Then we show that the steady-state distribution of the restoration model can be effectively calculated by a semiconvergent iterative aggregation-disaggregation method for block matrices. Finally, we compute the associated reliability function and hazard rate of the multipath transport system.

Peer-to-Peer Transfers for Crowd Monitoring - A Reality Check

Abstract: Peer-to-peer transfers allow for sharing crowd monitoring data despite the loss of network connectivity. However, limited insight into real-world deployment contexts can let the protocol design go astray - particularly, if a certain nature of participant behaviour and connectivity changes is assumed. This paper focuses on the delivery of crowd monitoring data. It puts a protocol out for a reality check that switches to peer-to-peer (p2p) communication when the infrastructure network connection is lost. The evaluation at an annual indoor fair asked visitors to make their phones visible to peers, run the protocol, and share crowd monitoring data. The results show that most of the participants formed a large radio cluster throughout the event. This made p2p networking only possible and enabled a more robust upload of crowd monitoring data. However, dynamic switching between infrastructure network and p2p communication also increased the volatility of the system, calling for future optimizations. The presented measurement results provide further insights into these details.

Infinite-Server Queue Model \(MMAP_{k}(t)|G_{k}|\infty \) with Time Varying Marked Map Arrivals of Customers and Occurrence of Catastrophes

Abstract: In the present paper, the infinite-server queue model \(MMAP_{k}(t)|G_{k}|\infty \) in transient MMAP random environment with time varying marked MAP arrival of k types of customers subject to catastrophes is considered The transient joint probability generating functions (PGF) of the number of different types of customers present in the model at moment t and the number of different types of customers departing from the system in the time interval (0, t] are found The Laplace-Stieltjes transform (LST) of total volume of customers being in service at moment t is defined The basic differential equations for joint probability generating functions of the number of busy servers and served customers for transient and stationary random environment are obtained