JungYul Choi

Centralized Scheduling Mechanism for Enhanced End-to-End Delay and QoS Support in Integrated Architecture of EPON and WiMAX

The integration of Ethernet Passive Optical Network (EPON) with IEEE 802.16 (WiMAX) is regarded as a promising access solution in realizing fixed mobile convergence (FMC) networks. The complementary features of EPON and WiMAX can bring not only wide bandwidth and mobility to subscriber stations (SS) but also economic efficiency to network providers. For successful convergence of EPON and WiMAX, there are some technical issues to resolve bandwidth allocation and QoS support in the MAC layer. Specifically, the independent scheduling (IS) mechanism to transmit data between EPON and WiMAX can cause performance degradation. For realizing EPON and WiMAX integration, this paper investigates three possible integrated architecture: independent ONU-BS (IOB), combined ONU-BS (COB), and hybrid ONU-BS (HOB). The emphasis on this paper is how to reduce the End-to-End (ETE) delay between EPON and WiMAX. For doing this, we propose a centralized scheduling (CS) mechanism that shortens the packet delay and the time of transmitting data upon requesting bandwidth for the SS. Simulation results witness that the proposed CS mechanism improves ETE delay, throughput, and QoS support compared to the IS when the cycle time of EPON and the frame size of WiMAX are 1 ms and 5 to 10 ms, as well as 2 ms and 5 ms, respectively.

Enhanced power-saving mechanism to maximize operational efficiency in IEEE 802.16e systems

A Power-Saving Mechanism (PSM) operates with sleep-mode and wake-mode, based on the receipt of requests for transition to each mode. The sleep-mode operation is manipulated by adjusting operating parameters such as the minimum sleep interval (Tmin) and the maximum sleep interval (Tmax). Interestingly, both energy consumption and the response delay of the request for a BS initiation of awakening are reciprocally affected by the relative sizes of these two operating parameters compared to the sleep duration (from the beginning of sleep-mode to that of wake-mode). To resolve this issue, this paper proposes a new PSM, called EPSM, which adaptively and simultaneously controls the operating parameters by efficiently reflecting the sleep duration. Moreover, depending on the current remaining energy state, this mechanism can also increase the available sizes of the operating parameters to be manipulated for achieving more intensive energy conservation. A numerical model is developed with a Markov chain for performance evaluation of the proposed mechanism pertaining to energy consumption and the response delay. The evaluation results substantiate that this mechanism can enhance energy conservation within reasonable response delay compared to the standard mechanism. Moreover, under an insufficient remaining energy state, the EPSM can prolong battery life while enduring an increasing response delay.

Scheduled power-saving mechanism to minimize energy consumption in IEEE 802.16e systems

A mobile station in IEEE 802.16e operates power management using sleep-mode operation with one or more connections supporting several applications. After all of the connections of an MS transit into the sleep state, the MS powers down and then goes into an unavailable state without communicating with the serving base station. To improve energy conservation, this letter proposes a new scheduled power-saving mechanism, which schedules sleep-mode operations for connections, which newly initiate sleep-mode, by controlling operating parameters, such as the minimum sleep interval (Tmin) and the maximum sleep interval (Tmax), and the initiation time of sleepmode operations of low quality of service (QoS) connections. Performance results show that the proposed mechanism can reduce the available state of an MS through this scheduling, and thus achieve better energy conservation of the MS than the standard mechanism.

Distributed antenna-based EPON-WiMAX integration and its cost-efficient cell planning

Achieving the benefits of high-capacity of optical networks and the mobility feature of wireless networks leads to integrate EPON and WiMAX for a promising broadband access solution. To efficiently put both benefits together, we propose an integration architecture of EPON-WiMAX based upon a Distributed Antenna (DA) environment, where collaborative Base Stations (BSs) concurrently transmit same wireless downlink signals (specifically for multicast and broadcast services (MBSs)) to Mobile Stations (MSs) in overlapped cell coverage areas. It helps enlarge the region of the available network coverage area by increasing Signal to Interference and Noise Ratio (SINR) in overlapped cell coverage areas through cooperation between Optical Line Terminal (OLT) and Optical Network Unit (ONU)- BS. We also present an cost-efficient cell planning to optimally control the size of overlapped cell coverage areas for the proposed DA-based integration architecture with a case study under a required region of the available network coverage area in consideration of the number of ONU-BSs and the distance between ONU-BSs. Performance evaluation results show that the proposed DA-based integration architecture enhances cost efficiency compared to the Traditional Antenna (TA) (non-DA)-based integration architecture with a similar level of spectral efficiency of MSs.

Trade-off guidelines for power management mechanism in the IEEE 802.16e MAC

Power management is an important part of the emerging standard of IEEE 802.16e (mobile WiMAX). The sleep-mode operation in power management helps to increase the life of a station by saving energy consumed, but at the same time it increases the response delay of awakening medium access control (MAC) service data units (SDUs). Its performance metrics, energy consumption and the average response delay of awakening MAC SDUs, are affected by correlations among the initial sleep window (Tmin), the final sleep window (Tmax), and the average interarrival time of awakening MAC SDUs (TI) during sleep-mode operation. There is a trade-off relationship between the performance metrics, so it is imperative to determine the most effective size for the two windows, Tmin and Tmax, in order to reduce energy consumption and still maintain a reasonable response delay time. To reach a fuller understanding of this problem, this paper first models sleep-mode operation in an IEEE 802.16e system and analyzes the effects of the size of the windows on the performance. Based on this analysis, the authors then present a decision making process for leveraging the two performance metrics by manipulating the size of the windows. The decision making process aims to provide some guidelines for determining the most advantageous size of each window to achieve the targeting performance goals.

Design of novel passive optical switching system using shared wavelength conversion with electrical buffer

We propose a novel optical switching system equipped with shared wavelength converters with electrical buffers. Simulation results show that the proposed system significantly reduces the blocking probability below 10-6 with low buffering delay. We present benefits of the proposed switching system compared with the conventional dedicated wavelength converter scheme in terms of blocking probability and average delay time. The proposed switching system is believed to be a technoeconomically feasible and implementable solution for optical packet/burst switching with current optical technologies.

Performance Evaluation of the Sleep Mode Operation in the EEE 802.16e MAC

The sleep mode operation is a significant part in power management in IEEE 802.16e for increasing life time of a station by saving energy consumption. In this operation, two key performance metrics, energy consumption and frame response delay, should be taken into account. These metrics are affected by initial sleep window (Tmin), final sleep window (Tmax), and average interarrival time (T1) of MAC frame to initiate awakening. Thus, this paper models the sleep mode operation in the IEEE 802.16e MAC and evaluates the effect of Tmin and Tmax on the performance of power management by considering T1. An analytical model for the operation is validated from computer simulation.

A tree-based slot allocation algorithm for loss-free slotted OBS networks

Optical burst switching (OBS) is regarded as one of the most promising switching technologies for next generation optical networks. However, the data burst contention problem is still unresolved thoroughly even though slotted OBS (SOBS) is studied as a new paradigm reducing the blocking rate. In this article, we propose a tree-based slot allocation (TSA) algorithm for loss-free SOBS networks, where the TSA algorithm originally avoids contention of the time-slots by reserving the time-slots with different time-slot positions for the source nodes, respectively. In order to manage the time-slots efficiently, we also propose an OBS superframe, which is a cyclic period and consists of multiple time-slots transmitted by the source nodes toward the same incoming port of a destination node. In addition, we attempt to optimize multiplexing of the OBS superframes to reduce wavelength consumption. On the other hand, when incoming traffic is beyond expectation, a source node may need more time-slots to prevent packet loss because of buffer overflow. For reallocation of the time-slots, we propose a flow control scheme managing some number of shared time-slots, where a control node adaptively allocates (or redeems) the time-slots to (or from) source nodes by utilizing the shared time-slots based on fluctuating traffic condition. Simulation results show that the blocking rate of the proposed TSA–OBS scheme is zero with acceptable queueing delay at moderate traffic offered loads. In addition, multiplexing optimization simulated in the 14-node NSFNET achieves a 63% reduction of wavelength consumption. Moreover, the proposed flow control scheme assisting the TSA algorithm maintains a target upper-bound of queueing delay at the source node, so that packet loss caused by buffer overflow is prevented.

An Adaptive Loss-Aware Flow Control Scheme for Delay-Sensitive Applications in OBS Networks

Optical Burst Switching (OBS) is one of the most promising switching technologies for next generation optical networks. As delay-sensitive applications such as Voice-over-IP (VoIP) have recently become popular, OBS networks should guarantee stringent Quality of Service (QoS) requirements for such applications. Thus, this paper proposes an Adaptive Loss-aware Flow Control (ALFC) scheme, which adaptively decides on the burst offset time based on loss-rate information delivered from core nodes for assigning a high priority to delay-sensitive application traffic. The proposed ALFC scheme also controls the upper-bounds of the factors inducing delay and jitter for guaranteeing the delay and jitter requirements of delay-sensitive application traffic. Moreover, a piggybacking method used in the proposed scheme accelerates the guarantee of the loss, delay, and jitter requirements because the response time for flow control can be extremely reduced up to a quarter of the Round Trip Time (RTT) on average while minimizing the signaling overhead. Simulation results show that our mechanism can guarantee a 10 -3 loss-rate under any traffic load while offering satisfactory levels of delay and jitter for delay-sensitive applications.

Service traffic management system for multiservice IP networks: lessons learned and applications

Next-generation networks offer new opportunities and challenges to Internet service providers as well as providers of other online services. Service providers can now deploy new services over an IP network infrastructure without building their own networks. In an open network environment, the network resources of ISPs should be fairly open to third parties that plan to launch their own services over the network. To actively respond to the changing network paradigm, it is essential to measure the traffic of individual services, and to estimate their cost for cost accounting between service provider and ISP. However, current traffic measurement techniques only provide the total traffic volume in links, without reporting the operator whose services flow through the links. Some commercial products can classify traffic into each application at a specific spot, but we should install monitoring systems at every spot throughout the entire network in order to observe which service traffic flows in every link. To satisfy the requirements of the NGN environment, we developed the Service Traffic Management System that can analyze the traffic of individual services based on user log data. STMS can report not only the traffic of individual services in every link, but also user behavior for each service. In addition, this article shares our experience of STMS development. We also introduce how we utilize STMS in IP network design, and discuss business and management support.