Chuck Yoo

One-way delay estimation and its application

Delay estimation is a difficult problem in computer networks. Accurate one-way delay estimation is crucial because it serves a very important role in network performance and thus application design. RTT (Round Trip Time) is often used as an approximation of the delay, but because it is a sum of the forward and reverse delays, the actual one-way delay cannot be estimated accurately from RTT. To estimate one-way delay accurately, this paper proposes a new scheme that analytically derives one-way delay, forward and reverse delay, respectively. We show that the performance of TCP can improve dramatically in asymmetric networks using our scheme. A key contribution of this paper is that our one-way delay estimation is much more accurate than RTT estimation so that TCP can quickly find the network capacity in the slow start phase. Since RTT is the sum of the forward and reverse delays, our scheme can be applied to any protocol that is based on RTT.

Eliminating the performance anomaly of 802.11b

In this paper, we propose a mechanism to eliminate the performance anomaly of IEEE 802.11b. Performance anomaly happens when nodes that have different transmission rates are in the same wireless cell. All the nodes in the cell might experience the same throughput even though their transmission rates are different because DCF of WLAN provides equal probability of channel access, but it does not guarantee the equal utilization of the wireless channel among the nodes. To reduce such a performance anomaly, we adjust the frame size proportionally depending on the bit rate. Additionally, our scheme eliminates the performance anomaly in multi-hop case. Simulation study shows that our scheme achieves an improvement in the aggregate throughput and the fairness.

Scalable ROI algorithm for H.264/SVC-based video streaming

H.264/SVC has been widely adopted to smart CE devices for network-adaptive video transmission. However, current H.264/SVC does not support sufficiently high subjective QoS (Quality of Service) because its scalability methods provide only coarse-grained network adaptivity. To address this problem, we propose Scalable ROI (SROI) algorithm that applies ROI (Region of Interests) concept to SVC (Scalable Video Codec). While existing methods use fixed size of enhancement layers, our method utilizes only ROI area as an enhancement layer so that it can improve subjective QoS with low transmission overhead. Through some experiments, we show that our method can increase PSNR (Peak Signal-to-Noise Ratio) by 4∼5 dB in ROI areas.

MobiVMM: a virtual machine monitor for mobile phones

Mobile phones have evolved into complex systems as they have more and more new applications built-in. As a result, they are less reliable and less secure than before. Virtual Machine Monitors (VMM) or hypervisors have been introduced to help the reliability and security of mobile phones but the existing research does not completely address three issues critical to mobile phones: real-time support, resource limitation, and power efficiency. In this paper we propose building a new VMM called MobiVMM for mobile phones to deal with these issues. MobiVMM enables real-time support using priority based scheduling and a pseudo-polling mechanism. Resource and power efficiency is achieved through light-weight design and implementation, highly customized guest operating systems, and a virtual hardware abstraction layer. We present our design considerations and report some preliminary experimental results based on the OMAP 2430 development platform.

A Step to Support Real-Time in Virtual Machine

Real-time is one of the unique requirements in embedded systems. In this paper, we perform a feasibility study on how to support real-time in an embedded virtual machine system. Firstly, we argue that the I/O model of the current virtual machine monitor like Xen is not suitable to support real-time applications because it lacks in predictability and it does not guarantee a deterministic I/O processing. We provide an alternative I/O model for virtualized embedded systems. Devices are categorized into four groups: dedicated, active, running, dynamic. Dedicated devices make a virtual machine simple because they do not need to be virtualized for isolation. However, dedication does not mean the performance isolation. Our experimental results with dedicated device show that traditional dedication cannot guarantee the timely responsiveness in heavy interrupt cases. Specifically, responsiveness of real-time OS degrades as interrupt load increases. There-ore, a proper interrupt control mechanism is required at virtual machine monitor level in order to support timely responsiveness. In addition, our result supports that 1) short and prioritized interrupt processing helps responsiveness in a virtual machine system; 2) smaller time quantum results in better responsiveness also.

HAVS: hybrid adaptive video streaming for mobile devices

This paper presents a new Scalable Video Codec (SVC)-based hybrid adaptive video streaming scheme, named HAVS, for mobile devices in wireless environments. The proposed approach takes two existing video streaming technologies, viz., progressive download and adaptive streaming, and switches them in a hybrid manner. To this end, HAVS employs the H.264/SVC encoding scheme, where each video chunk is encoded into one base layer and several enhancement layers. Since clients request the base layer every time a video is streamed, HAVS performs progressive download for the base layer and adaptive streaming for the enhancement layers. Through wireless test-bed experiments, it is demonstrated that the proposed scheme can be easily implemented on mobile devices without any server-side modification. This scheme effectively prevents video freeze thereby providing better quality video streaming than the existing non-hybrid streaming technologies.

Toward under-millisecond I/O latency in Xen-ARM

This paper addresses the I/O latency issue within Xen-ARM. Although Xen-ARMs split driver presents reliable driver isolation, it requires additional inter-VM scheduling. Consequently, the credit scheduler within Xen-ARM results in unsatisfactory I/O latency for real-time guest OS. This paper analyzes the I/O latency in Xen-ARMs interrupt path, and proposes a new scheduler to bound I/O latency. Our scheduler dynamically assigns priorities to guest OSs so that Xen-ARM ensures to schedule the most urgent task within the system. The experimental results show that Xen-ARM with our new scheduler reduces delay spikes, latency larger than 1ms, from 16% to 1% while retaining the split driver model.

DAoT: Dynamic and energy-aware authentication for smart home appliances in Internet of Things

The Internet of Things (IoT) is beneficial to individuals, business, and society because it creates a wide range of value-added services by interconnecting diverse devices and information objects. However, as IoT devices have resource constraints to employ powerful security mechanisms, they are vulnerable to sophisticated security attacks such as the main-in-the-middle (MITM) attack. Therefore, an intelligent authentication mechanism that considers both resource constraints and security is required. In this paper, we suggest a dynamic and energy-aware authentication scheme for the Internet of Things (DAoT). DAoT uses a feedback control scheme to dynamically select an energy-efficient authentication policy. With DAoT, IoT devices with limited resources can be safely interconnected because DAoT finds and adopts the best cost-effective authentication mechanism.

Network interface virtualization in wireless communication for multi-streaming service

In this paper, we suggest a multiple streaming method with virtualized network interface in wireless environment. A virtualization provides new interface mechanism to system by mitigating restrictions of hardware. Our virtualized system which has virtualized network interface can communicate with multiple AP(Access Point)s as system has several network interfaces in wireless environment. Each several virtualized network interface connect with several APs. The most stable connection becomes main-connection and others become sub-connections. By this mechanism we can improve streaming performance such as multi-path streaming without relay server, ensuring flexibility for mobile communication, providing better quality of service with SVC encoded video and improving error resilience in wireless environment.

Analytic end-to-end estimation for the one-way delay and its variation

Delay estimation is a difficult problem in computer networks. RTT (round trip time) is often used as an approximation of the delay, but because it is a sum of the forward and reverse delays, the actual one-way delay cannot he estimated accurately from RTT. Accurate one-way delay estimation becomes crucial because it serves a very important role in network and application design. This paper proposes a new scheme to estimate one-way delay and its variation. The scheme calibrates estimated one-way delay so in a brief duration as to be used in many protocols that adjust their behavior depending on the network condition. We analytically derive one-way delay, forward and reverse delay respectively, and show that our one-way delay estimation is much more accurate than RTT estimation by simulation.