Title: YouSlow: What Influences User Abandonment Behavior for Internet Video?
Authors: Hyunwoo Nam and Henning Schulzrinne
Tech report

Abstract: With the proliferation of online video, measuring quality of experience (QoE) has become a crucial aspect for the analysis of today's over-the-top (OTT) video streaming. To monitor video QoE, we introduce YouSlow, a monitoring tool that can detect various playback events (e.g., start-up delay, rebufferings and bitrate changes) from video players while a video is being played. Using YouSlow, we have collected more than 1,400,000 YouTube views from more than 110 countries. We measured the impact of these playback events on video abandonment and found that about 10% of viewers abandoned YouTube videos when the pre-roll ads lasted for 15 seconds. We observe that more viewers abandoned YouTube videos when they suffered from the initial buffering than the rebufferings in the middle of a playback. Our regression analysis shows that bitrate changes do not affect video abandonment significantly and the abandonment rate can be estimated accurately using the rebuffering ratio and the number of rebufferings (R² = 0.94).

Title: QoE Matters More Than QoS: Why People Stop Watching Cat Videos
Authors: Hyunwoo Nam, Kyung-Hwa Kim and Henning Schulzrinne
Published in: IEEE INFOCOM 2016

Abstract: With the proliferation of online video, measuring quality of experience (QoE) has become a pivotal aspect for the analysis of today's over-the-top (OTT) video streaming. To monitor video QoE, we introduce YouSlow that can detect various playback events (e.g., start-up latency, rebufferings and bitrate changes) from video players while a video is being played. Using YouSlow, we have collected more than 400,000 YouTube views from more than 100 countries. We measured the impact of these playback events on video abandonment and found that rebufferings incur abandonment rates six times higher than start-up latency, mostly caused by pre-roll ads. A single rebuffering event has three times the impact of a bitrate change. Even increasing the bitrate can raise abandonment rates by a factor of four compared to keeping the bitrate constant.

Title: Generating Realistic YouTube-like Stall Patterns for HTTP Video Streaming Assessment
Authors: Martín Varela, Hyunwoo Nam, Henning Schulzrinne, and Toni Mäki
Published in: IEEE QOMEX 2016

Abstract: Abstract—In this short paper we briefly describe the results of analyzing a large-scale data set of actual YouTube stall patterns collected world-wide as part of Columbia University’s YouSlow project, and how we used it to create a simple model for generating realistic stalling patterns with a given number of stalls, a given average stall duration, and a pattern structure (describing the relative length of the stalling events). These stall patterns can be used to perform subjective assessment of HTTP video under realistic conditions. A tool for generating the patterns and the data accompanying this paper has been released for the research community to use.

Title: Towards Dynamic MPTCP Path Control Using SDN
Authors: Hyunwoo Nam, Doru Calin and Henning Schulzrinne
Published in: IEEE NETSOFT 2016

Abstract: MPTCP (MultiPath TCP) boosts application network performance by aggregating bandwidth over multiple paths. However, it may cause poor performance due to the large number of out-of-order packets especially when the paths have different bandwidths and delays. To resolve this issue, we propose to dynamically add or remove MPTCP paths with the leverage of software-defined networking (SDN). The key idea is to track the available capacity of connected paths and pick the most appropriate paths depending on varying network conditions. To show the feasibility of our approach, we create an SDN platform using Mininet over Wi-Fi networks. Our analysis shows that a faster download and improved quality of experience (QoE) in adaptive rate video streaming is possible with our dynamic MPTCP path control mechanism using SDN.

Title: Intelligent Content Delivery over Wireless via SDN
Authors: Hyunwoo Nam, Doru Calin and Henning Schulzrinne
Published in: IEEE WCNC 2015 Best paper

Abstract: On the Internet, most traffic is generated by content delivery applications such as video streaming, P2P and web surfing. With the proliferation of mobile applications that offer on-demand access to services, the ability to track end-users' perceived service quality has become a pivotal aspect for future networks such as 5G. Software defined networking (SDN) and network functions virtualization (NFV) in the mobile core offer unprecedented flexibility for opportunistic traffic steering, leading to advanced levels of quality-of-service (QoS) control. We leverage the SDN concept to dynamically control network traffic over wide area networks (WANs) from edge nodes of wireless networks (e.g., a PDN gateway in LTE), depending on changing network conditions and application types. Our SDN-based application-aware routing system allows mobile network operators to achieve better utilization of their networks, service providers to improve customer satisfaction, and end-users to experience desirable service quality for various network applications. As for a prototype, we attach 802.11g to Mininet's virtual networks in order to show the feasibility of our approach.

Title: Towards QoE-aware Video Streaming using SDN
Authors: Hyunwoo Nam, Kyung-Hwa Kim, Jong Yul Kim and Henning Schulzrinne
Published in: IEEE GLOBECOM 2014

Abstract: Today's over the top (OTT) video service providers take advantage of content distribution networks (CDNs) and adaptive bitrate (ABR) streaming where a video player adjusts resolutions based on end-to-end network conditions. Although the mechanisms are useful to improve user-perceived video quality, they do not resolve the root causes of congestion problems. To pinpoint a bottleneck and improve video quality-of-experience (QoE), we leverage a software-defined networking (SDN) platform from OTT video service provider's point of view. Our proposed SDN application is designed to monitor network conditions of streaming flow in real time and dynamically change routing paths using multi-protocol label switching (MPLS) traffic engineering (TE) to provide reliable video watching experience. We use an off- the-shelf SDN platform to show the feasibility of our approaches.

Title: YouSlow: A Performance Analysis Tool for Adaptive Bitrate Video Streaming
Authors: Hyunwoo Nam, Kyung-Hwa Kim, Doru Calin and Henning Schulzrinne
Published in: ACM SIGCOMM 2014 POSTER

Abstract: Adaptive bitrate (ABR) technologies are being widely used in today’s popular HTTP-based video streaming such as YouTube and Netflix. Such a rate-switching algorithm em- bedded in a video player is designed to improve video quality- of-experience (QoE) by selecting an appropriate resolution based on the analysis of network conditions while the video is playing. However, a bad viewing experience is often caused by the video player having difficulty estimating transit or client-side network conditions accurately. In order to ana- lyze the ABR streaming performance, we developed YouS- low, a web browser plug-in that can detect and report live buffer stalling events to our analysis tool. Currently, YouS- low has collected more than 20,000 of YouTube video stalling events over 40 countries.

Title: Towards Dynamic Network Condition-Aware Video Server Selection Algorithms over Wireless Networks
Authors: Hyunwoo Nam, Kyung-Hwa Kim, Doru Calin and Henning Schulzrinne
Published in: IEEE ISCC 2014

Abstract: We investigate video server selection algorithms in a distributed video-on-demand system. We conduct a detailed study of the YouTube Content Delivery Network (CDN) on PCs and mobile devices over Wi-Fi and 3G networks under varying network conditions. We proved that a location-aware video server selection algorithm assigns a video content server based on the network attachment point of a client. We found out that such distance-based algorithms carry the risk of directing a client to a non optimal content server, although there may exist other better performing video delivery servers. In order to solve this problem, we propose to use dynamic network information such as packet loss rates and Round Trip Time (RTT) between an edge node of a wireless network (e.g., an Internet Service Provider (ISP) router in a Wi-Fi network and a Radio Network Controller (RNC) node in a 3G network) and video content servers, to find the optimal video content server when a video is requested. Our empirical study shows that the proposed architecture can provide higher TCP performance, leading to better viewing quality compared to location-based video server selection algorithms.

Title: Towards Dynamic QoS-aware Over-The-Top Video Streaming
Authors: Hyunwoo Nam, Kyung-Hwa Kim, Bong Ho Kim, Doru Calin and Henning Schulzrinne
Published in: IEEE WOWMOM 2014 in Best paper finalist

Abstract: We present a study of traffic behavior of two pop- ular over-the-top (OTT) video streaming services (YouTube and Netflix). Our analysis is conducted on different mobile devices (iOS and Android) over various wireless networks (Wi-Fi, 3G and LTE) under dynamic network conditions. Our measurements show that the video players frequently discard a large amount of video content although it is successfully delivered to a client. We first investigate the root cause of this unwanted behavior. Then, we propose a Quality-of-Service (QoS)-aware video streaming architecture in Long Term Evolution (LTE) networks to reduce the waste of network resource and improve user experience. The architecture includes a selective packet discarding mechanism, which can be placed in packet data network gateways (P-GW). In addition, our QoS-aware rules assist video players in selecting an appropriate resolution under a fluctuating channel condition. We monitor network condition and configure QoS parameters to control availability of the maximum bandwidth in real time. In our experimental setup, the proposed algorithm (and platform) achieves nearly 21% improvement in downlink bandwidth saving, creating a better user experience under challenging radio conditions.

Title: A Mobile Video Traffic Analysis: Badly Designed Video Clients Can Waste Network Bandwidth
Authors: Hyunwoo Nam, Bong Ho Kim, Doru Calin and Henning Schulzrinne
Published in: IEEE GLOBECOM 2013 WORKSHOP

Abstract: Video streaming on mobile devices is on the rise. According to recent reports, mobile video streaming traffic accounted for 52.8% of total mobile data traffic in 2011, and it is forecast to reach 66.4% in 2015. We analyzed the network traffic behaviors of the two most popular HTTP-based video streaming services: YouTube and Netflix. Our research indicates that the network traffic behavior depends on factors such as the type of device, multimedia applications in use and network conditions. Furthermore, we found that a large part of the downloaded video content can be unaccepted by a video player even though it is successfully delivered to a client. This unwanted behavior often occurs when the video player changes the resolution in a fluctuating network condition and the playout buffer is full while downloading a video. Some of the measurements show that the discarded data may exceed 35% of the total video content.

Title: Application-aware Routing Platform Using SDN
Authors: Hyunwoo Nam, Kyung-Hwa Kim and Henning Schulzrinne
Published in: NYC Media Lab's Summit Demo 2014

Abstract: We introduce an application-aware routing platform using software-defined networking (SDN). SDN provides programmatic traffic control in software over both physical and virtual network devices. We take advantage of the SDN platform to dynamically control network traffic over wide area networks (WANs), depending on changing network conditions and service types. Our SDN-based application-aware routing system allows 1) network operators to achieve better utilization of capacity in their networks, 2) service providers to improve customer satisfaction, and 3) end-users to have better service quality for various network applications. In the demo, we show the feasibility of our approach and introduce our monitoring system in a simulated WAN network.

Title: Flexible Network Address Mapping for Container-based Clouds
Authors: Kyung-Hwa Kim, Jae Woo Lee, Michael Ben-Ami, Hyunwoo Nam, Jan Janak and Henning Schulzrinne
Published in: IEEE NETSOFT 2015 (short paper)

Abstract: Container-based clouds have recently received great attention from the industry. However, we notice that this new type of cloud inevitably requires complex network setups and configurations from both providers and customers when deployed on an existing cloud system; Providers need to install additional network elements such as proxy servers and Network Address Translation (NAT), and customers need to use subdomain names and randomly assigned port numbers to access their services. Thus, we propose a new network architecture that performs Mto-N mapping between network addresses and containers in order to simplify the network setup and configuration. To achieve our goals, we adopt a software-defined networking (SDN) approach. We discuss the benefits and use cases of our approach, and present detailed designs and implementation.

Title: MoT: A Collaborative Network Troubleshooting Platform for the Internet of Things
Authors: Kyung-Hwa Kim, Hyunwoo Nam, Jin-Hyung Park and Henning Schulzrinne
Published in: IEEE WCNC 2014

Abstract: Troubleshooting network problems on networked home devices is not easy, because most devices have insufficient computing power to run sophisticated diagnostic tools and have no user interfaces to debug the problem directly. We propose MoT, a network problem diagnosis platform that leverages the collaboration of smart objects, smartphones, and computers. We take advantage that recent devices have multiple communication interfaces. Therefore, when a device has a problem with an interface, it can send a probe request to other devices using an alternative interface. We use collaborative mechanisms to diagnose the root cause of a network problem. It can use coop- eration from internal nodes or send requests to external nodes. We demonstrate the feasibility of this approach by implementing an Android application and an algorithm that diagnoses a push notification failure.

Title: DYSWIS: Crowdsourcing a Home Network Diagnosis
Authors: Kyung-Hwa Kim, Hyunwoo Nam, Vishal Singh, Daniel Song and Henning Schulzrinne
Published in: IEEE ICCCN 2014

Abstract: Existing failure diagnostic techniques for end users are insufficient to pinpoint the root causes of network failures due to their limited capabilities to probe other net- work elements. We present DYSWIS, an automatic network fault detection and diagnosis system for end-users. DYSWIS leverages user collaboration to distinguish important network faults from false positive indications, and diagnoses the root cause of the fault using diagnostic rules that consider diverse information from multiple nodes. Our rule system is specially designed to support crowdsourcing and distributed probes. We have implemented DYSWIS and compared its performance with other tools to prove that several network failures which are difficult to be diagnosed by the single-user probe can be detected and diagnosed successfully with our approach.

Title: WiSlow: A Wi-Fi Network Performance Troubleshooting Tool for End Users
Authors: Kyung-Hwa Kim, Hyunwoo Nam and Henning Schulzrinne
Published in: IEEE INFOCOM 2014

Abstract: Slow Internet connectivity is often caused by poor Wi-Fi performance. The main reasons of such performance degra- dation include channel contention and non-Wi-Fi interference. Although these problem sources can be easily removed in many cases once they are discovered, it is difficult for end users to identify the sources of such interference. We investigated the characteristics of different sources that can degrade Wi-Fi performance, and developed WiSlow, a software tool that diagnoses the root causes of poor Wi-Fi performance using user-level network probes, and leveraging peer collaboration to identify the physical location of these causes. WiSlow uses two main methods: packet loss analysis and 802.11 ACK number analysis. The accuracy of WiSlow exceeds 90% when the sources are close to Wi-Fi devices. Also, our experiment proves that the collaborative approach is feasible for determining the relative location of an interfering device.

Title: WiSlow: A Performance Troubleshooting Tool for Wi-Fi Networks
Authors: Kyung-Hwa Kim, Hyunwoo Nam and Henning Schulzrinne
Published in: USENIX NSDI 2014 POSTER

Abstract: Today, it is common for a household to install a wire- less Access Point (AP) for its home network. How- ever, the increasing number of APs and wireless devices inevitably results in more contention and interference, which causes unsatisfactory Wi-Fi network performance. Furthermore, isolating the root causes of poor perfor- mance is nontrivial because the problem may be caused by collision with packets from other Wi-Fi devices us- ing the same channel, i.e., channel contention or interfer- ence from non-Wi-Fi devices such as microwave ovens, cordless phones, and baby monitors. Since these devices and 802.11b/g operate on the same 2.4-GHz spectrum, they generate severe interference when they operate to- gether. Although these sources of problems can be easily removed in many cases (e.g., by relocating the baby monitor), it is difficult for technically non-savvy users to even notice the existence of channel contention or non-Wi-Fi interference. Instead, properly working routers or service providers are frequently misidentified as the culprit.

Title: On Access Control in the Internet of Things
Authors: Jan Janak, Hyunwoo Nam, and Henning Schulzrinne
Published in: IETF 2012

Abstract: Existing authorization frameworks, commonly used to control access to online services and nodes in the Internet, are role based and not suitable for IP based networks of sensors, actuators, and controllers. First, the identity of the user is established and then his or her access privileges are determined from the user's role within an organization. A light actuator, for example, does not need to know the identity of the switch, as long as the switch can prove that it is located in the same room. Even ordinary actuators, and controllers in the real world are subject to access control restriction. There, authorization decisions are usually made based on a number of attributes claimed by the controller, not identity. We are designing an attribute based authorization framework for IoT devices to be used to implement common access restrictions that had been present in those actuators and controllers before they were upgraded and connected to the Internet. We want to be able to keep such devices connected to the global network, while preserving common access restrictions (now implemented in software).