LaeYoung Kim

Dynamic Deflection Routing with Virtual Wavelength Assignment in Optical Burst-Switched Networks

In optical burst-switched networks, one of the most significant issues is contention resolution. There have been several deflection routing techniques as contention resolution. While contention is resolved by traditional deflection routing, it cannot guarantee that the control packet will reserve all the wavelengths successfully to the destination on the alternate path, especially when traffic load in a network is high. Therefore, in this paper, we propose a Deflection Routing with Virtual Wavelength Assignment (DR-VWA) algorithm in order to provide a higher resource guarantee for loss-sensitive traffic bursts. The proposed DR-VWA scheme (1) dynamically decides the alternate path with the least traffic load and (2) allows high-priority bursts in terms of loss to be assigned available wavelengths over the path virtually. The proposed scheme is evaluated through simulation, and it is shown that significant improvement with regard to burst loss and wavelength conversion cost can be achieved.

Dropping Policy with Burst Retransmission to Improve the Throughput of TCP Over Optical Burst-switched Networks

A major concern in optical burst-switched (OBS) networks is contention, which occurs when more than one bursts contend for the same data channel at the same time. Due to the bufferless nature of OBS networks, these contentions randomly occur at any degree of congestion in the network. When contention occurs at any core node, the core node drops bursts according to its dropping policy. Burst loss in OBS networks significantly degrades the throughput of TCP sources in the local access networks because current TCP congestion control mechanisms perform a slow start phase mainly due to contention rather than heavy congestion. However, there has not been much study about the impact of burst loss on the performance of TCP over OBS networks. To improve TCP throughput over OBS networks, we first introduce a dropping policy with burst retransmission that retransmits the bursts dropped due to contention, at the ingress node. Then, we extend the dropping policy with burst retransmission to drop a burst that has experienced fewer retransmissions in the event of contention at a core node in order to reduce the number of events that a TCP source enters the slow start phase due to contention. In addition, we propose to limit the number of retransmissions of each burst to prevent severe congestion. For the performance evaluation of the proposed schemes, we provide an analytic throughput model of TCP over OBS networks. Through simulations as well as analytic modeling, it is shown that the proposed dropping policy with burst retransmission can improve TCP throughput over OBS networks compared with an existing dropping policy without burst retransmission.

OPN05-2: Congestion Control Scheme based on Peak Load in Optical Burst Switching Networks

The most important design goal in Optical Burst Switching (OBS) networks is to reduce burst loss resulting from resource contention. Especially, the higher the congestion degree in the network is, the higher the burst loss rate becomes. To improve the burst loss performance, this paper proposes a novel congestion control scheme that operates based on the highest (called peak load) of the loads of all links over the path between each pair of ingress and egress nodes in an OBS network. This paper also proposes an algorithm that dynamically determines a load threshold for adjusting burst sending rate, according to the traffic load in a network. Simulation results show that the proposed scheme reduces the burst loss rate significantly, compared to existing OBS protocols (with and without congestion control), while maintaining reasonable throughput and fairness.

A dynamic load-aware congestion control scheme in optical burst switching networks

The most important design goal in Optical Burst Switching (OBS) networks is to reduce burst loss resulting from resource contention. Especially, the higher the congestion degree in the network is, the higher the burst loss rate becomes. The burst loss performance can be improved by employing an appropriate congestion control. In this paper, to actively avoid contentions, we propose a dynamic load-aware congestion control scheme that operates based on the highest (called ‘peak load’) of the loads of all links over the path between each pair of ingress and egress nodes in an OBS network. We also propose an algorithm that dynamically determines a load threshold for adjusting burst sending rate, according to the traffic load in a network. Further, a simple signalling method is developed for our proposed congestion control scheme. The proposed scheme aims to (1) reduce the burst loss rate in OBS networks and (2) maintain reasonable throughput and fairness. Simulation results show that the proposed scheme reduces the burst loss rate significantly, compared to existing OBS protocols (with and without congestion control), while maintaining reasonable throughput and fairness. Simulation results also show that our scheme keeps signalling overhead due to congestion control at a low level.

Dropping policy for improving the throughput of TCP over optical burst-switched networks

Burst loss due to contention in Optical Burst-Switched (OBS) networks significantly degrades the throughput of TCP sources in the local access networks because TCP congestion control mechanism makes a TCP source enter a slow start phase regardless of the congestion degree of OBS networks In this paper, to improve TCP throughput over OBS networks, we first introduce a dropping policy (DP) with retransmission of the bursts dropped due to contention, by the ingress node Then, we extend the DP with retransmission to drop a burst that has experienced fewer retransmissions in the event of contention in order to reduce the number of events that a TCP source enters the slow start phase due to contention Additionally, we propose to limit the number of retransmissions of each burst to prevent severe congestion For the performance evaluation of the proposed schemes, we provide an analytic model of TCP throughput over OBS networks It is shown via numerical and simulation results that the proposed schemes can achieve better TCP throughput performance than an existing DP without retransmission.

MIPv6-Based Power Saving Scheme in Integrated WLAN and Cellular Networks

In the integrated Wireless LAN (WLAN) and cellular networks, power efficiency is one of the most important aspects as in existing wireless networks. Especially, we note that in the idle state, a mobile device with dual interfaces needs to receive periodic beacons from the access point and downlink control information from the base station, resulting in significant power consumption. To save the power, we propose a power saving scheme with Hibernation mode to completely turn off the WLAN interface during the idle state, instead of entering Power Save (PS) mode and turn it on only when there is a need to receive data. However, if the WLAN interface is turned on even for a momentary traffic, it must repeat turning on and off continuously, dissipating power. Thus, we also develop a Mobile IPv6 (MIPv6)-based signaling to turn on the WLAN interface for long-lived traffic. It is shown via simulations that the proposed power saving scheme results in better power efficiency.

Peak Load-Based Congestion Control Scheme in Optical Burst Switching Networks

A method for controlling congestion based on peak load values in optical burst switching networks is provided to maintain reasonable level in the aspect of flow rate fairness and signaling overhead. A method for controlling congestion based on peak load values in optical burst switching networks comprises the following steps of: periodically transmitting load messages from an output node to an input node(s100); processing the load messages received from an intermediate node and transmitting an NAK(Negative Acknowledge Character) message to the input node(s200); increasing/decreasing a burst transmission rate by comparing NAK messages or peak-load value with the load message(s300); and initializing the NAK messages to zero by a congestion controlling unit(s400).

A Power Saving Scheme for Heterogeneous Wireless Access Networks

In integrated WLAN and cellular networks, we propose a power saving scheme that completely turns off WLAN interface in the idle state and wakes it up when there is incoming data from long-lived traffic. We also develop a Mobile IPv6 (MIPv6)-based signaling to turn on the WLAN interface only for long-lived traffic. It is shown via simulations that the proposed power saving scheme improves power efficiency over typical WLAN system.

Performance improvement of TCP over optical burst switching networks with drop policy

In Optical Burst Switching (OBS) networks, the TCP performance is significantly affected by burst loss. This is because burst loss in OBS networks occurs mostly due to contention instead of heavy congestion so that a Time Out (TO) event will trigger unnecessary TCP congestion control resulting in significant throughput degradation. However, there has not been much study about the impact of burst loss on the performance of TCP over OBS networks. Therefore, in this paper, we propose a Drop Policy (DP) with burst retransmission where a new concept of retransmission-count for bursts is introduced to mitigate unnecessary TCP congestion control. For the performance evaluation of the proposed DP, we provide an analytical throughput model of TCP over OBS networks. The analytical and simulation results show that the TCP throughput is improved by our proposed DP with burst retransmission.

Novel congestion control scheme in next-generation optical networks

In this paper, to improve the burst loss performance, we actively avoid contentions by proposing a novel congestion control scheme that operates based on the highest (called peak load) of the loads of all links over the path between each pair of ingress and egress nodes in an Optical Burst Switching (OBS) network.