Jihoon Sung

Multipath Video Real-Time Streaming by Field-Based Anycast Routing

Wireless mesh networking (WMN) for video surveillance provides a strong potential for rapid deployment in a large community, for which reliability and survivability for real-time streaming are the key performance measure. However, current routing protocols do not provide a robust solution to meet video transmission requirements such as providing load balancing for the high data rate and delay requirements. We propose an application of field-based anycast routing (FAR) protocol, which utilizes rapid routing dynamics inspired by an electrostatic potential field model governed by Poissons equation. This routing metric takes into account geometric proximity and congestion degree in order to increase delivery ratio and decrease end-to-end delay, which determine the quality of the delivered video. In addition, FAR protects node failure with an on-the-fly rerouting process that guarantees the continuity of video streaming. Simulation results show 100% delivery ratio in congestion situations and it shows tolerance to different delay requirements compared with AODV and FDMR protocols in terms of delivering real-time and non real-time video surveillance which verifies FAR as a strong candidate for video transmission over WMN.

Greedy Local Routing Strategy for Autonomous Global Load Balancing Based on Three-Dimensional Potential Field

We discuss a traffic load balancing scheme for three-dimensional (3D) wireless mesh networks (WMNs), which deals with global load balancing through only one-hop local information. With a finite element method (FEM), we derive a distributed form of a solution for 3D Poissons equation to construct a routing metric sensitive to traffic loads. For practical validation, we implement it on an IEEE 802.11-based WMN testbed platform. Experiment results show that our protocol chooses routing paths more efficiently for network-wide load balancing than a state-of-the-art routing protocol, OLSR-ETX.

Efficient Cache Placement Strategy in Two-Tier Wireless Content Delivery Network

Internet content caching for multimedia services has received much attention mainly in the field of large-scale wired networking as a primary solution to save network resources and improve quality of service (QoS). Rapidly increasing consumption of multimedia content in mobile networks brings a challenge of how to efficiently deliver content in local wireless access networks. Cache embedment in wireless mesh environment is an intriguing attempt to enhance the QoS and service capacity, leading to the question of how to design an efficient content delivery network considering the inherent characteristics of the wireless environment. We propose and investigate an efficient cache placement strategy in novel two-tier wireless content delivery networks, which utilize separate channels for content dissemination and content service. Such a two-tier network system model helps to achieve much better content delivery performance with a greatly reduced system design complexity compared to single-tier network system models. Further, we incorporate a delay cost due to contention, which is mainly responsible for performance in shared-medium wireless networks, as a key metric for cache placement under the system model. After formally formulating the cache placement problem, we propose a cross-layer heuristic algorithm and demonstrate its performance compared with an optimal solution by integer linear programming. Simulation results show significant performance improvements by our strategy compared to the performance of existing representative strategies in terms of service delay, packet delivery ratio, and the amount of delivered packets within a given delay deadline.

Joint optimization of cache server deployment and request routing with cooperative content replication

Content delivery network (CDN) with a high quality-of-service (QoS) requirement deals with three challenging problems: 1) a cache server deployment problem to determine where to locate cache servers, 2) a request routing problem to settle which cache server serves a user request, and 3) a content replication problem to decide which content is stored in a cache server. Cooperation among cache servers significantly improves the user QoS by increasing the cached content diversity of the network. Since the aforementioned problems are tightly coupled, we formulate a new CDN model which jointly considers all the three problems under the cooperative content replication with optimal solutions using integer linear programming. As the joint optimization problem is an NP-hard problem, we propose a greedy heuristic algorithm which is close to the optimal solution. We consider two scenarios for application of the algorithm, where the popularities of contents are identical and are different among nodes. The performance of the algorithm is investigated on the actual topology sampled from the Level 3 CDN network. By increasing the cached content diversity in the network, the joint optimization problem under the cooperative content replication shows higher performance than that of the non-cooperation case.

Energy-aware algorithms for network-assisted device-to-device content delivery networks

Due to explosively growing demands for mobile contents, network-assisted device-to-device (D2D) content delivery networks (CDNs) have emerged as an ancillary resource for content services. The key characteristics of the network system is that mobile devices are used as cache servers for localized content delivery via D2D communication that controlled by a cellular network. Recently, a few studies have reported that it can provide better content delivery performance at a low cost. However, mobile devices operating as cache servers have to inevitably make sacrifices for energy consumption by delivering requested contents to neighboring requesters. In this paper, we tackle the critical problem and finally propose two energy-aware algorithms: request routing and MAC scheduling. Simulation results exhibit that the algorithms can reconcile conflicting objectives such as extending the D2D network lifetime and achieving good content delivery performance.

Efficient cache placement strategy for wireless content delivery networks

An efficient cache placement strategy for wireless content delivery networks is devised for a novel wireless mesh content distribution network model using two independent channels for content dissemination and content access. An efficient interference metric is defined to estimate congestion in wireless environments to formulate the cache placement problem by integer linear programming. Simulation results exhibit the benefit of our approach compared to existing hop-count based schemes.

Efficient Content Replacement in Wireless Content Delivery Network with Cooperative Caching

Wireless content delivery networks (WCDNs) have received attention as a promising solution to reduce the network congestion caused by rapidly growing demands for mobile content. The amount of reduced congestion is intuitively proportional to the hit ratio in a WCDN. Cooperation among cache servers is strongly required to maximize the hit ratio in a WCDN where each cache server is equipped with a small-size cache storage space. In this paper, we address a content replacement problem that deals with how to manage contents in a limited cache storage space in a reactive manner to cope with a dynamic content demand over time. As a new challenge, we apply reinforcement learning, which is Q-learning, to the content replacement problem in a WCDN with coooperative caching. We model the content replacement problem as a Markov Decision Process (MDP) and finally propose an efficient content replacement strategy to maximize the hit ratio based on a multi-agent Q-learning scheme. Simulation results exhibit that the proposed strategy contributes to achieving better content delivery performance in delay due to a higher hit ratio, compared to typical existing schemes of least recently used (LRU) and least frequently used (LFU).

A novel content caching replacement strategy inspired by a human memory system

We propose an innovative content caching replacement strategy for future content delivery networks. Ultimately, we provide new insight in caching design by the inspiration of a human memory system.

One-touch caching for content delivery in wireless consumer networks

As consumer traffic rapidly increases, content caching becomes common in intermediate nodes for rapid content transportation reducing content-trip delay. Compared with wired content caching systems, wireless caching systems require a lighter-weight caching mechanism because of limited processing capability. In this paper, we address that one-touch caching just keeping the most-recently requested content and replacing a random content among existing contents for storage of the new content significantly enhances caching performance with little computational overhead. Through simulation results, it is demonstrated that our scheme shows hit-ratio comparable to LFU (least-frequently-used) and LRU (least-recently-used) caching strategies.