Kideok Cho

WAVE: Popularity-based and collaborative in-network caching for content-oriented networks

In content-oriented networking, content files are typically cached in network nodes, and hence how to cache content files is crucial for the efficient content delivery and cache storage utilization. In this paper, we propose a content caching scheme, WAVE, in which the number of chunks to be cached is adjusted based on the popularity of the content. In WAVE, an upstream node recommends the number of chunks to be cached at its downstream node, which is exponentially increased as the request count increases. Simulation results reveal that the average hop count of content delivery of WAVE is lower than other schemes, and the inter-ISP traffic volume of WAVE is the second lowest (CDN is the lowest). Also, WAVE achieves higher cache hit ratio and fewer frequent cache replacements than other on-demand caching strategies.

SCAN: Scalable Content Routing for Content-Aware Networking

Since Internet routers are not aware of the contents being forwarded, the same content file is often delivered multiple times inefficiently. Similarly, users cannot exploit a nearby copy of the content of interest unless the content file is serviced by costly content delivery networks. Prior studies on the content-aware routing for efficient content delivery suffer from the scalability problem due to a large number of contents. We propose a scalable content routing, dubbed SCAN, which can exploit nearby and multiple content copies for the efficient delivery. SCAN exchanges the information of the cached contents using Bloom filter. Compared with IP routing, SCAN can offer reduced delivery latency, reduced traffic volume, and load balancing among links.

How can an ISP merge with a CDN

As delivering contents has become the dominant usage of the Internet, efficient content distribution is one of the hottest research areas in the network community. In future networks, it is anticipated that network entities such as routers will be equipped with in-network storage due to the trend of ever decreasing storage cost. In this article, we propose a novel content delivery architecture called ISP-centric content delivery (iCODE) by which an ISP can provide content delivery services as well. iCODE can provide efficient content delivery services since an ISP can cache contents in routers with storage modules considering traffic engineering and the locality of the content requests. Compared to CDN and P2P systems, iCODE can offer reduced delivery latency by placing the contents closer to end hosts, and incentives to ISPs by reducing inter- ISP traffic and allowing traffic engineering. We also discuss the technical and business issues to realize the iCODE architecture.

REACT: Rate Adaptation using Coherence Time in 802.11 WLANs

The channel coherence time in indoor WLANs normally exceeds multiple frame transmission times. In light of this, we propose a new rate adaptation scheme, termed as the Rate Adaptation using Coherence Time (REACT), that has the following key features. First, without exchanging RTS and CTS frames, the receiver in REACT informs the transmitter of the improved channel condition via altering the ACK transmission rate, so that the transmitter increases the data rate for subsequent data frames. This enables the transmitter to adapt to the time-varying channel conditions while inducing the marginal overhead. Second, the transmitter in REACT can identify the reasons of frame losses by exploiting the feedback from the receiver and the estimated coherence time. Frame losses are assumed to be caused only by collisions for the duration of the coherence time after receiving an ACK frame with the altered bit rate. The coherence time is also used to enhance the adaptive RTS probing, so that the REACT can prevent the transmitter from decreasing its bit rate when collisions occur. Extensive simulations reveal that REACT consistently performs better than the other rate adaptation schemes (ARF, CARA, RRAA, and RBAR) in all the testing scenarios.

Publisher mobility support in content centric networks

As the high speed Internet and the smart devices become prevalent, it is expected that the traffic volume of the video conferencing/broadcasting on the mobile devices is increasing explosively. One of the promising solutions for the traffic explosion problem is the content centric networking (CCN), which solves the problem by focusing on the content instead of the location. Even though CCN can provide better delivery efficiency, robustness, security, and native subscriber mobility, little attention is paid to the publisher mobility problem, where the mobile devices produce the real-time traffic. In this paper, we propose PMC, a publisher mobility support protocol in CCN. By introducing two names and corresponding operations at the routers, PMC supports publisher mobility for the mobile video conferencing and broadcasting without violating the original CCN architecture. We believe that PMC is a validated and secured scheme following the philosophy of the CCN architecture to support mobile publisher.

Content discovery for information-centric networking

The information-centric networking (ICN) adopts a content name as a network identifier and utilizes in-network storages to cache the contents. With the name-based routing and content caching, ICN can provide substantial benefits such as faster content retrieval and network traffic reduction by exploiting a nearby (cached) copy of content and reducing duplicated transmissions for the same content request. Prior researches on ICN usually rely on an opportunistic cache-hit (happen-to-meet) to utilize the in-network storages. In the happen-to-meet fashion, only the content cached on the path towards the content source can be utilized, which limits the network-wide usage of the in-network storages. To exploit cached contents better, we propose a content discovery scheme, dubbed SCAN, which can exploit nearby content copies for the efficient delivery. SCAN exchanges the cached content information among the neighbor routers using Bloom filters for the content discovery. With extensive simulations, SCAN shows better performance than a happen-to-meet cache-hit scheme in terms of average hop counts, traffic volume, and load balancing among links.

A probabilistic and opportunistic flooding algorithm in wireless sensor networks

In wireless sensor networks, many communication protocols and applications rely on flooding for various networking purposes. Prior efforts focus on how to design efficient flooding algorithms; that is, they seek to achieve full reliability while reducing the number of redundant broadcasting across the network. To achieve efficient flooding, most of the existing protocols try to reduce the number of transmissions, which is decided without considering any online transmission result. In this paper, we propose a probabilistic and opportunistic flooding algorithm that controls rebroadcasts and retransmissions opportunistically. It seeks to achieve a target reliability required by an application. For this purpose, it makes a given node select only the subset of its one-hop neighbors to rebroadcast the same message. It considers node relations such as link error rates among nodes in selecting eligible neighbors to rebroadcast. The sender controls the number of retransmissions opportunistically by tracking the current status of message reception at its neighbors. Simulation is carried out to reveal that our proposed scheme achieves the given target reliability with less overhead than other flooding algorithms in most cases, thus prolonging the network lifetime.

SRMS: SIP-based RFID Management System

Radio frequency identification (RFID) is a new technology for object identification/tracking systems. In this paper, we propose a novel RFID location management system: SIP-based RFID management system (SRMS). SRMS employs session initiation protocol (SIP), which is an Internet standard protocol for session management and mobility support. SRMS enhances the existing SIP architecture by introducing a surrogate user agent (SUA) and an SRMS name server (SNS). The SUA performs location registration procedures on behalf of RFID tags with limited capabilities, while the SNS provides name resolution services for location registration/tracking of RFID tags. To evaluate the location registration latency in SRMS, we carry out performance analysis based on queueing models. Compared with the existing RFID management systems, SRMS has advantages of service extensibility and reusability.

Decentralized and autonomous content overlay networking (DACON) with WiFi access points

Accessing contents from mobile devices becomes more and more proliferated and hence the need for the content distribution in the pervasive environment is growing. However, distributing contents in such environments taxes wireless network operators substantially. To provide the content distribution service in a reasonable cost, we pay attention to user-deployable WiFi access points (APs). In this paper, we propose a decentralized and autonomous content overlay networking (DACON) architecture for the pervasive content distribution services, which is the overlay network architecture comprised of public WiFi APs. We identify and answer major challenges in realizing the content distribution service in the pervasive environment by exploiting the overlay network of public WiFi APs.

Waterfall: Video Distribution by Cascading Multiple Swarms

Video on demand services have been increasingly proliferated in the Internet. One popular way to disseminate video files among numerous users is to leverage peer-to-peer (P2P) systems (e.g., BitTorrent). However, BitTorrent is not designed with video streaming requirements and hence suffers from long setup delay. In this paper, the drawbacks of existing P2P-based streaming solutions are analyzed in terms of sequential delivery. Then we propose Waterfall that splits the whole swarm into multiple swarms, which are then cascaded by the scene sequence. In this way, peers in a swarm download the chunks of the same video scene from the peers in the same swarm as well as the ones in the preceding swarm that already moved on to the next scene. The average setup delay and maximum playback rate of Waterfall are analyzed. Experiments from a wide area network testbed reveal that Waterfall achieves two to three times higher playback rate and significantly low setup delay than the prior BitTorrent-based streaming solutions.