Yangwoo Ko

InterX: A service interoperability gateway for heterogeneous smart objects

Due to the advances in wireless networking and microelectronics, more and more smart objects are equipped with wireless networking as well as high computing capability. Heterogeneity of service protocols inhibits the interoperation among smart objects using different service protocols. Existing works overcome the heterogeneity by assuming that service protocols used are known in advance so that components necessary for interoperations can be deployed before runtime. This assumption prevents existing works from being applied to situations where a user wants to spontaneously configure her smart objects to interoperate with smart objects found nearby without (or with minimal) user intervention. In this paper, we propose a service interoperability gateway that discovers service protocols used in a given environment, finds smart objects using these protocols, and instantiates proxies for interoperability between smart objects.

An Overlay-Based Resource Monitoring Scheme for Social Applications in MANET

The popularity of Social Networking Service and the ubiquity of handheld devices improve chances of social interactions. Mobile social software emerges as a key part of this new trend. In order for users to enjoy this social experience, the resource state of member needs to be monitored so applications can adapt to dynamics of MANET and resource constraints on mobile devices. Previous work in resource monitoring for MANETs focuses on providing a general monitoring scheme. Therefore important group semantics, such as membership information, are not considered. This lack of consideration generates unnecessary traffic overhead and delay in responses. In this paper, we propose a resource monitoring scheme for group-based applications in MANETs. The proposed scheme is based on clusters of information that communicate each other using a group-based overlay. An evaluation shows that the proposed scheme shows shorter response time and smaller traffic overhead without accuracy degradation compared with previous work.

A Reactive Local Positioning System for Ad Hoc Networks

Existing ad hoc location systems measure locations proactively by continuous measurements and communication among all nodes in an ad hoc network. However, in certain location-based applications only a few nodes need the location of a few other nodes, in which case the proactive approach results in an unnecessarily large overhead. We propose a scheme for a reactive ad hoc location system, which avoids the overhead of a proactive scheme by limiting multi- lateration and coordination of coordinate systems to nodes centered around the route between the source node requesting the location and the target node whose location is being requested. Simulations show that our scheme reduces overheads substantially compared to an existing proactive scheme.

A social transitivity-based data dissemination scheme for opportunistic networks

A social-based routing protocol for opportunistic networks considers the direct delivery as forwarding metrics. By ignoring the indirect delivery through intermediate nodes, it misses chances to find paths that are better in terms of delivery ratio and time. To overcome this limitation, we propose to incorporate transitivity, which considers the indirect delivery through intermediate nodes, as one of the forwarding metrics. We also found that some message forwards do not improve the delivery performance. To reduce the number of these useless forwards, the proposed scheme forwards messages to an encountered node when the increase of total utility value is greater than a threshold. Using a simulator with real world trace data sets, we compare the proposed scheme with the existing protocols, epidemic routing and SimBetTS. Compared with SimBetTS, the proposed scheme increases delivery ratio by 1.5 percent and decreases delay time by 2 percent while reducing overhead by 30 percent.

Interference-aware routing protocol in multi-radio wireless mesh networks

Utilization of multiple radio interfaces increases throughput of wireless networks. Existing work proposes a multi-radio routing protocol exploiting link quality and channel diversity of a path. While an established path is deteriorated by interferences incurred by any changes in a network, and existing work does not detect the deterioration. In this paper, we propose an interference-aware multi-radio routing protocol detecting and resolving dynamic path deterioration in wireless mesh networks.

SGR: A Shared Generic Routing Support for Ad Hoc Ubiquitous Computing Environments

One of the most evident characteristics of an ad hoc ubiquitous computing environment is the dynamism of connections. Due to the mobility of nodes, paths between communicating peers change over time and hence should be discovered continually. Applications also dynamically discover available services and replace connections to provide contextually more appropriate services. In such an environment, the reduction of discovery cost and the reflection of context are main design factors. In order to avoid discovery cost being paid by both application and routing layer and to delay a service binding until forwarding time, we propose a shim layer called shared generic routing (or SGR) that discovers paths by accommodating application layer labels as well as IP addresses as routing targets and manages forwarding states. On top of SGR, IP and application layer routing can be efficiently implemented. Through simulation, we show that SGR can effectively remove duplicated discovery efforts.

An Efficient Shared Learning Scheme for Layered Video Streaming over Application Layer Multicast

Layered video multicast such as RLM (Receiver- driven layered multicast) is a promising technique for delivering streaming video to a set of heterogeneous receivers over ALM (Application Layer Multicast) as well as over IP multicast. However, this approach may suffer from unnecessary fluctuation of video quality due to overlapped and failed join-experiments. Though a shared learning scheme was introduced to resolve these problems in IP multicast-based layered video streaming, it may cause high control overhead and slow convergence problem when used with ALM. In this paper, we propose a new shared learning scheme for ALM-based layered video multicast which reduces control overhead and convergence latency while keeping the number of fluctuation reasonably small. Through the analysis of link sharing in ALM, we redefine the range of receivers that are affected by overlapped or failed join-experiments and incorporate it into the proposed scheme. The simulation results show that the proposed scheme performs better than an ALM-based layered video multicast with shared learning in terms of control overhead and convergence latency.

A nondisruptive multi-path handoff scheme for peer-to-peer live video streaming

The key challenge to provide a seamless peer-to-peer live video delivery over mobile heterogeneous networks is to handle dynamic changes of networks due to vertical handoff. To adapt to the network changes, it is required to support path adaptation which changes an overlay path by selecting a new sending peer and adjusts a reception rate to the new overlay path. In order to handle the path adaptation seamlessly, multi-path handoff schemes have been proposed, which preserve an old overlay path in an overlapped area while adapting to a new network. In the existing schemes, however, flows from old and new paths may compete for the bandwidth of a shared link with each other and this causes users video quality degradation during handoff, which we call a shared bottleneck problem. We propose a nondisruptive handoff scheme to solve the shared bottleneck problem. By detecting a shared bottleneck link when probing potential paths, the proposed scheme adjusts underestimated bandwidth of potential paths during peer selection and makes the flow from an old path yield its bandwidth smoothly during rate adaptation.

A Nondisruptive Adaptation Scheme for Peer-to-Peer Live Video Streaming during Vertical Handoff

In this paper, we propose QoS-constrained peer selection and nondisruptive rate adaptation schemes with considering shared bottleneck problem to provide a stable peer-to-peer live video streaming service during vertical handoff. In the proposed scheme, a QoS-constrained peer is selected by estimating bandwidth with active probing, and a reception rate converges to a stable state without any QoS degradation with help of multi-path handoff. The shared bottleneck problem is addressed by adjusting the estimated bandwidth and yielding the redundant bandwidth usage.