arXiv subjects

Mohamed Othman

Publications and source records attributed to Mohamed Othman.

26 records · Page 2Linked to original sources

arXiv2016

Agile-SD: A Linux-based TCP Congestion Control Algorithm for Supporting High-speed and Short-distance Networks

Recently, high-speed and short-distance networks are widely deployed and their necessity is rapidly increasing everyday. This type of networks is used in several network applications; such as Local Area Networks (LAN) and Data Center Networks (DCN). In LANs and DCNs, high-speed and short-distance networks are commonly deployed to connect between computing and storage elements in order to provide rapid services. Indeed, the overall performance of such networks is significantly influenced by the Congestion Control Algorithm (CCA) which suffers from the problem of bandwidth under-utilization, especially if the applied buffer regime is very small. In this paper, a novel loss-based CCA tailored for high-speed and Short-Distance (SD) networks, namely Agile-SD, has been proposed. The main contribution of the proposed CCA is to implement the mechanism of agility factor. Further, intensive simulation experiments have been carried out to evaluate the performance of Agile-SD compared to Compound and Cubic which are the default CCAs of the most commonly used operating systems. The results of the simulation experiments show that the proposed CCA outperforms the compared CCAs in terms of average throughput, loss ratio and fairness, especially when a small buffer is applied. Moreover, Agile-SD shows lower sensitivity to the buffer size change and packet error rate variation which increases its efficiency.

cs.NI↗

arXiv2016

Greedy-Knapsack Algorithm for Optimal Downlink Resource Allocation in LTE Networks

The Long Term Evolution (LTE) as a mobile broadband technology supports a wide domain of communication services with different requirements. Therefore, scheduling of all flows from various applications in overload states in which the requested amount of bandwidth exceeds the limited available spectrum resources is a challenging issue. Accordingly, in this paper, a greedy algorithm is presented to evaluate user candidates which are waiting for scheduling and select an optimal set of the users to maximize system performance, without exceeding available bandwidth capacity. The greedy-knapsack algorithm is defined as an optimal solution to the resource allocation problem, formulated based on the fractional knapsack problem. A compromise between throughput and QoS provisioning is obtained by proposing a class-based ranking function, which is a combination of throughput and QoS related parameters defined for each application. The simulation results show that the proposed method provides high performance in terms of throughput, loss and delay for different classes of QoS over the existing ones, especially under overload traffic.

cs.NI↗

arXiv2015

Giant Gain Enhancement in Photonic Crystals with a Degenerate Band Edge

We propose a new approach leading to giant gain enhancement. It is based on unconventional slow wave resonance associated to a degenerate band edge (DBE) in the dispersion diagram for a special class of photonic crystals supporting two modes at each frequency. We show that the gain enhancement in a Fabry-Perot cavity (FPC) when operating at the DBE is several orders of magnitude stronger when compared to a cavity of the same length made of a standard photonic crystal with a regular band edge (RBE). The giant gain condition is explained by a significant increase in the photon lifetime and in the local density of states. We have demonstrated the existence of DBE operated special cavities that provide for superior gain conditions for solid-state lasers, quantum cascade lasers, traveling wave tubes, and distributed solid state amplifiers. We also report the possibility to achieve low-threshold lasing in FPC with DBE compared to RBE-based lasers.

physics.optics↗

arXiv2015

Theory and New Amplification Regime in Periodic Multi Modal Slow Wave Structures with Degeneracy Interacting with an Electron Beam

We present the theory of a new amplification regime in Travelling Wave Tubes (TWTs) composed of a slow-wave periodic structure that supports multiple electromagnetic modes that can all be synchronized with the electron beam. The interaction between the multimodal slow-wave structure and the electron beam is quantified using a Multi Transmission Line approach (MTL) based on a generalized Pierce model and transfer matrix analysis leading to the identification of modes with complex Bloch wavenumber. In particular, we address a new possible operation condition for TWTs based on the super synchronism between an electron beam and four modes exhibiting a degeneracy condition near a band edge of the periodic slowwave MTL. We show a phenomenological change in the band structure of periodic MTL where we observe at least two growing modal cooperating solutions as opposed to a uniform MTL interacting with an electron beam where there is rigorously only one growing modal solution. We discuss the advantage of using such a degeneracy condition in TWTs that leads to larger gain conditions in amplifier regimes and also to very lowstarting beam current in high power oscillators.

physics.optics↗

arXiv2015

Demonstration of a Degenerate Band Edge in Periodically-Loaded Circular Waveguides

We demonstrate the existence of a special degeneracy condition, called degenerate band edge (DBE), between two Bloch modes in periodically loaded circular all-metallic waveguides at microwave frequencies. The DBE condition has been associated with a dramatic reduction in group velocity and with some unique resonance properties, but it has not been shown in hollow waveguide structures yet. Hence, we show here its existence in two periodic waveguide examples. The unit cell of the first case is composed of a circular waveguide loaded with two inner cylinders with elliptical irises with misaligned angles. The second structure is composed of loading the waveguide with elliptical rings. The demonstration of DBE in those waveguide is explained through a simple multi transmission line approach where the conditions to obtain DBE are clarified, and suggests that the DBE can occur in several other analogous periodic waveguide. These structures can be potentially used to investigate unconventional gain schemes in traveling wave tubes or other kinds of distributed amplifiers and novel pulse compressors.

physics.optics↗

arXiv2012

Optimizing Service Differentiation Scheme with Sized-based Queue Management in DiffServ Networks

In this paper we introduced Modified Sized-based Queue Management as a dropping scheme that aims to fairly prioritize and allocate more service to VoIP traffic over bulk data like FTP as the former one usually has small packet size with less impact to the network congestion. In the same time, we want to guarantee that this prioritization is fair enough for both traffic types. On the other hand we study the total link delay over the congestive link with the attempt to alleviate this congestion as much as possible at the by function of early congestion notification. Our M-SQM scheme has been evaluated with NS2 experiments to measure the packets received from both and total link-delay for different traffic. The performance evaluation results of M-SQM have been validated and graphically compared with the performance of other three legacy AQMs (RED, RIO, and PI). It is depicted that our M-SQM outperformed these AQMs in providing QoS level of service differentiation.

cs.NI↗

arXiv2010

Analytical Evaluation of Unfairness Problem in Wireless LANs

The number of users using wireless Local Area Network is increasing exponentially and their behavior is changing day after day. Nowadays, users of wireless LAN are using huge amount of bandwidth because of the explosive growth of some services and applications such as video sharing. This situation imposes massive pressure on the wireless LAN performance especially in term of fairness among wireless stations. The limited resources are not distributed fairly in saturated conditions. The most important resource is the access point buffer space. This importance is a result of access point being the bottleneck between two different types of networks. These two types are wired network with relatively huge bandwidth and wireless network with much smaller bandwidth. Also the unfairness problem is keep getting worse because of the greedy nature Transmission Control Protocol (TCP). In this paper, we conduct a comprehensive study on wireless LAN dynamics and proposed a new mathematical model that describes the performance and effects of its behavior. We validate the proposed model by using the simulation technique. The proposed model was able to produce very good approximation in most of the cases. It also gave us a great insight into the effective variables in the wireless LAN behavior and what are the dimensions of the unfairness problem.

cs.NI↗

arXiv2010

Evaluation Study for Delay and Link Utilization with the New-Additive Increase Multiplicative Decrease Congestion Avoidance and Control Algorithm

As the Internet becomes increasingly heterogeneous, the issue of congestion avoidance and control becomes ever more important. And the queue length, end-to-end delays and link utilization is some of the important things in term of congestion avoidance and control mechanisms. In this work we continue to study the performances of the New-AIMD (Additive Increase Multiplicative Decrease) mechanism as one of the core protocols for TCP congestion avoidance and control algorithm, we want to evaluate the effect of using the AIMD algorithm after developing it to find a new approach, as we called it the New-AIMD algorithm to measure the Queue length, delay and bottleneck link utilization, and use the NCTUns simulator to get the results after make the modification for the mechanism. And we will use the Droptail mechanism as the active queue management mechanism (AQM) in the bottleneck router. After implementation of our new approach with different number of flows, we expect the delay will less when we measure the delay dependent on the throughput for all the system, and also we expect to get end-to-end delay less. And we will measure the second type of delay a (queuing delay), as we shown in the figure 1 bellow. Also we will measure the bottleneck link utilization, and we expect to get high utilization for bottleneck link with using this mechanism, and avoid the collisions in the link.

cs.NI↗