Burst contention occurs when attempting to transmit several optical bursts at the time into the same core router output port. This is a shortcoming of the Optical Burst Switching (OBS) networks and for this reason it has been challenging to implement the OBS mode into the transport networks so far. This problem can be solved applying various contention resolution strategies at core nodes (fiber delay lines, wavelength conversion or deflection routing). The following question arises: how does data transmission through the OBS network quality depend on using such strategy combination in the core node? For these reasons an analytical model has been created to find out what impact a joint application of various contention resolution strategies has on the data transmission quality. An algorithm has been proposed for the burst service in the OBS core router when a contention arises. The authors suggest applying burst segmentation only for the lower priority bursts, reducing the lower priority data losses in the case of mixed priority burst incoming flow. Every additional burst collision resolution strategy increases the time spent at the node however, so it is highly important to determine by means of simulations the optimal amount of resources needed at the core node.
Abstract:Various underground communications (water or gas supply systems, sewage, power lines) have been installed in recent years using trenchless technologies, i.e. horizontal directional drilling (HDD). This technique by its nature does not disturb the traffic and is environmentally friendly. One must be aware that, with HDD, pipeline building time is shortened. With respect to the above, HDD is especially effective in highly populated or industrial areas. However, it is necessary to ensure that HDD works, in order to prevent damage to installed underground facilities. The aim of this work is to propose a user-friendly and inexpensive simulation tool with required functionality for HDD trajectoryplanning under field conditions. The optimization of HDD trajectory-planning consisted of analyzing the methods for pilot bore trajectory construction: step-by-step, six-point, and four-point control. The statistical evaluation of such methods revealed their similarity regarding time resources (when using any of the methods mentioned above, the upper limit of 95% confidence interval of HDD trajectory-planning duration does not exceed 1 min). The tests of the simulation tool at work places with Ditch Witch JT922 demonstrated good functionality due to its intuitive interface and simple and fast ability to replan a HDD trajectory. Increased accuracy of bore path planning and simpler pilot bore construction were achieved.
Using WDM multiplexing is one of the ways to increase PON bandwidth. But as WDM-PON is still expensive and difficult administered, the idea of using a Reflective Semiconductor Optical Amplifier (RSOA) is proposed. It can be installed in WDM-PON ONU network devices. A comprehensive problem analysis of various investigations is done relating to a performance of RSOA-based WDM-PON systems. The simulation model is created for RSOA-based WDM-PON access with downstream signal reusing in ONU for upstream transmission. This model helped in researching of RSOA abilities using different downstream and upstream signals modulation. Signal parameters were tested working with special software OptiSystem. Results were evaluated regarding such a characteristics as Q factor, signal attenuation, power and optical fiber length. It was found that RZ code was better suited in remodulation with RSOA; it achieved 1.25 Gbps signal transmission at a distance 8 times larger than that of the in NRZ code case.
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