Keuntae Park

Railroad: virtual infrastructure for data dissemination in wireless sensor networks

In this paper, we present Railroad, a data dissemination architecture for large-scale wireless sensor networks. Railroad system proactively exploits a virtual infrastructure called Rail, which is an area where all the metadata of event data are stored. There is only one Rail in the network and it acts as a rendezvous area of the events and the queries. Rail is placed in the middle area of the field so that every node can easily access it. Once a query is issued, it circulates around Rail and searches relevant data stored in Rail. When a relevant metadata is found, the source node of the data transmits the corresponding data to the sink node which has issued the query. By using Rail, Railroad achieves a scalable and energy-efficient data dissemination architecture under dynamic conditions with multiple mobile observers and targets. We evaluate and compare the communication cost and the hot spot message complexity of Railroad with previous approaches.

An Energy-Efficient Scheduling MAC Protocol for Wireless Sensor Networks

This paper proposes a novel MAC protocol for sensor networks which is energy efficient and has a good performance as well. Energy is the most important resource in battery-operated sensor networks. Sensor nodes need the wireless network interface to forward data and it has to be always awake to handle possible traffics. This occupies most energy wastes in sensor nodes and pervious works solved this problem by periodic listen and sleep. However, periodic listen and sleep causes the loss of performance. Our protocol also uses periodic sleeping but listen period are used for multi-hop schedule reservations and data transmission is delayed until schedule time. Schedules are reserved as data are pipelined for energy efficiency and performance. In addition, we suggest an energy efficient error recovery mechanism for data transmissions. We evaluate our protocol and compare with previous MAC protocols through ns-2 simulations.

Look-ahead scheduling for energy-efficiency and low-latency in wireless sensor networks

The operation of a sensor node is limited by the initially equipped battery which is hard to be recharged or replaced. Thus reducing unnecessary energy consumption is one of the most important requirements. Most energy waste is from the always-on wireless interface and many new MAC protocols have been suggested to solve the problem. However, they sacrifice the MAC latency, especially, with multi-hop forwarding.In our approach, we designed a novel MAC protocol which has both low latency and power efficiency by separating channel reservation process and data transmission process. The sensor nodes having data to forward are efficiently scheduled during reservation process. The other nodes with no schedule go to sleep to save energy and only scheduled nodes are awake during scheduled time and transmit data. The performance of our protocol is evaluated through simulations.

MTCP: A Transmission Control Protocol for Multi-Provider Environment

Transmission schemes that gain content from multiple servers concurrently have been highlighted due to their ability to provide bandwidth aggregation, stability on dynamic server departure, and load balancing. Previous approaches employ parallel downloading in the transport layer to minimize the receiver buffer size and maximize bandwidth utilization. However, they only focus on the receiver operations and induce considerable overhead at the senders in contradiction to the main goal of a multi-provider environment, offloading popular servers through replication. In the present work, the authors propose MTCP, a novel transport layer protocol that focuses on reduction of the sender overhead through the elimination of unnecessary disk I/Os and efficient buffer cache utilization. MTCP also balances trade-off objectives to minimize buffering at receivers and maximize the request locality at senders.

New peer-to-peer overlay network for content-based publish/subscribe systems

Publish/subscribe has become a prevalent model for distributed content delivery due to its ability to decouple communication between participants. It has remained a challenge to design a scalable overlay supporting the complexity of content-based publish/subscribe systems, while satisfying the desirable properties large distributed systems should have. This paper presents the design of Mirinae, a new structured peer-to-peer overlay mesh based on the interests of peers. To fulfil the gap between the rich subscription language of publish/subscribe and the logical address of overlay network, we devise a bloom-filter based mapping scheme. Given an event, Mirinae provides a flexible and efficient dissemination tree minimizing the participation of non-matching nodes. Our evaluation demonstrates that Mirinae is able to achieve its goals of scalability, efficiency, and adaptiveness.

A fast and highly adaptive peer-to-peer lookup system for medium-scale network

This paper presents the design and evaluation of FastAd, a fast and highly adaptive peer-to-peer (P2P) lookup system for medium-scale network where the number of nodes is not more than tens of thousands. Using routing tables larger than those of previous schemes, a lookup can be performed at just two hops, while maintenance cost of tables can be minimized by adopting lazy consistency with piggybacking. In addition, assigning dynamic node identifier (nodeId) instead of a fixed nodeId by hashing the nodes IP address, FastAd network can be organized more adaptively and adjusted dynamically with system state such as load distribution, node dynamics, and so on. As a result, each node has different responsibility to exploit its heterogeneity.

Mobility Aware Transmission Power Control in Mobile Ad-hoc Network

The energy efficient algorithm which saves network energy consumption by reducing transmission range in static networks cannot maintain the energy efficiency in dynamic networks because of link failure by node mobility and asymmetric links. So we present MATPC which keeps 20% better energy efficiency compare to other approaches in dynamic networks

Negotiation-based transport layer protocol for many-to-one transmission

Traditional approaches to utilize the multi-provider environment that has the servers with the same contents are classified into bandwidth aggregation on client-side and load reduction and balancing on server-side. However, previous approaches, client-side and server-side approaches, are hard to work together. In this paper, we present a transport layer protocol for many-to-one transmission that harmonies client and server reduction with a negotiation mechanism. It provides the way to inform clients of server contents and enhanced request distribution mechanism. Experimental results from our implementation on the Linux show that the protocol efficiently specializes each server for the certain contents while the out-of-order packets at clients are minimized

Thread-aware garbage collection for server applications

In recent years server applications using Java become popular. However, they have different performance requirements from other applications: high throughput and small response time. One of obstacles for achieving those requirements is a Java Virtual Machine (JVM). Among the services that a JVM provides, garbage collection affects server applications in throughput and latency. Some JVMs have various garbage collectors for server-side Java but they do not still consider the behavior of server applications. We show that the lifetime pattern of objects is distinguished by the thread that allocates them in server applications. Separating objects and applying different collection policies according to threads, we propose that a garbage collector can achieve both high throughput and small pause time. Experiments show that the throughput of our collector is up to 1.7 times greater than that of previous generational collectors with the same pause time and the pause time of minor collection is smaller by almost 10% given the same throughput.

Enhancing TCP performance over wireless network with variable segment size

TCP, which was developed on the basis of wired links, supposes that packet losses are caused by network congestion. In a wireless network, however, packet losses due to data corruption occur frequently. Since TCP does not distinguish loss types, it applies its congestion control mechanism to non-congestion losses as well as congestion losses. As a result, the throughput of TCP is degraded. To solve this problem of TCP over wireless links, previous researches, such as split-connection and end-to-end schemes, tried to distinguish the loss types and applied the congestion control to only congestion losses; yet they do nothing for non-congestion losses. We propose a novel transport protocol for wireless networks. The protocol called VS-TCP (Variable Segment size Transmission Control Protocol) has a reaction mechanism for a non-congestion loss. VS-TCP varies a segment size according to a non-congestion loss rate, and therefore enhances the performance. If packet losses due to data corruption occur frequently, VS-TCP decreases a segment size in order to reduce both the retransmission overhead and packet corruption probability. If packets are rarely lost, it increases the size so as to lower the header overhead. Via simulations, we compared VS-TCP and other schemes. Our results show that the segment-size variation mechanism of VS-TCP achieves a substantial performance enhancement.