Ikjun Yeom

Mobility support in content centric networks

Content-centric networking (CCN) is designed for efficient dissemination of information. Several architectures are proposed for CCN recently, but mobility issues are not considered sufficiently. We classify traffic types of CCN into real-time and non real-time. We examine mobility problems for each type, and suggest the possible hand-off schemes over CCN. Then, we analyze the delay performance in terms of simulation study. We believe that the proposed schemes can be merged as a part of the CCN easily, since they comply with the inherent nature and rules of the CCN.

TCP-Aware Uplink Scheduling for IEEE 802.16

In IEEE 802.16 networks, a bandwidth request-grant mechanism is used to accommodate various QoS requirements of heterogeneous traffic. However, it may not be effective for TCP flows since (a) there is no strict QoS requirement in TCP traffic; and (b) it is difficult to estimate the amount of required bandwidth due to dynamic changes of the sending rate. In this letter, we propose a new uplink scheduling scheme for best-effort TCP traffic in IEEE 802.16 networks. The proposed scheme does not need any bandwidth request process for allocation. Instead, it estimates the amount of bandwidth required for a flow based on its current sending rate. Through simulation, we show that the proposed scheme is effective to allocate bandwidth for TCP flows.

Performance analysis of in-network caching for content-centric networking

With the explosion of multimedia content, Internet bandwidth is wasted by repeated downloads of popular content. Recently, Content-Centric Networking (CCN), or the so-called Information-Centric Networking (ICN), has been proposed for efficient content delivery. In this paper, we investigate the performance of in-network caching for Named Data Networking (NDN), which is a promising CCN proposal. First, we examine the inefficiency of LRU (Least Recently Used) which is a basic cache replacement policy in NDN. Then we formulate the optimal content assignment for two in-network caching policies. One is Single-Path Caching, which allows a request to be served from routers only along the path between a requester and a content source. The other is Network-Wide Caching, which enables a request to be served from any router holding the requested content in a network. For both policies, we use a Mixed Integer Program to optimize the content assignment models by considering the link cost, cache size, and content popularity. We also consider the impact of link capacity and routing issues on the optimal content assignment. Our evaluation and analysis present the performance bounds of in-network caching on NDN in terms of the practical constraints, such as the link cost, link capacity, and cache size.

Modeling and Performance Analysis of Address Allocation Schemes for Mobile Ad Hoc Networks

Address allocation is an essential part in maintaining a mobile ad hoc network (MANET) effectively, and several address allocation schemes have been proposed. In this paper, we present a set of analytical models to evaluate the efficiency of address allocation schemes. The derived models quantitatively characterize the efficiency of four popular address allocation schemes in terms of latency and communication overhead. Through the analysis, we achieve numerical results that show the impact of network parameters on the efficiency of these schemes. We also conduct simulations and compare with analytical results to validate our models. The analytical model developed in this paper is able to more accurately predict the performance of address allocation schemes over a various range of loss rates and would be useful in providing more insights for the study of an efficient address allocation scheme in MANETs. To our understanding, this is the first attempt in mathematically investigating the performance of addressing schemes in ad hoc networks.

Active Queue Management for Flow Fairness and Stable Queue Length

Two major goals of queue management are flow fairness and queue-length stability However, most prior works dealt with these goals independently. In this paper, we show that both goals can be effectively achieved at the same time. We propose a novel scheme that realizes flow fairness and queue-length stability. In the proposed scheme, high-bandwidth flows are identified via a multilevel caching technique. Then, we calculate the base drop probability for resolving congestion with a stable queue, and apply it to individual flows differently depending on their sending rates. Via extensive simulations, we show that the proposed scheme effectively realizes flow fairness between unresponsive and TCP flows, and among heterogeneous TCP flows, while maintaining a stable queue.

Congestion control for sudden bandwidth changes in TCP

In this paper, we propose a novel technique to deal with sudden bandwidth changes in transmission control protocol (TCP). In the current Internet, sudden bandwidth changes may occur because of vertical handovers between heterogeneous access networks, routing path changes, cognitive ratio, and multi-rate wireless local area network. The current implementation of TCP is designed and optimized for stable networks and does not adapt well upon sudden bandwidth changes. Consequently, it might suffer from packet losses in burst upon sudden bandwidth decrement and under-utilization upon sudden bandwidth increment. To resolve this problem, we propose to modify the current TCP algorithm to include a new phase, called fast adaptation (FA). The FA phase is triggered upon detecting sudden bandwidth changes, and a TCP sender in the FA phase attempts to recover lost packets quickly to avoid spurious timeouts upon sudden bandwidth decrement. Upon sudden bandwidth increment, it increases its window size drastically to realize full utilization. Through extensive simulations, experiments, and analysis, it is shown that the proposed scheme can effectively deal with sudden bandwidth changes. Copyright

Distributed Fair Scheduling for Wireless Mesh Networks Using IEEE 802.11

In IEEE-802.11-based wireless mesh networks (WMNs), unfair bandwidth sharing may arise, because the carrier sense multiple access with collision avoidance protocol is designed to provide per-station fairness only in one hop. As the hop count from a mobile client to the gateway node increases, the throughput of the node drastically decreases. In this paper, we propose a fair bandwidth allocation scheme for multiradio multichannel WMNs. This scheme provides fair bandwidth sharing among the nodes in a WMN, regardless of their hop distance from the gateway node. To achieve fairness, we first estimate the number of active nodes attached to each router and calculate the effective weights of routers based on the estimation. Then, we differentiate their contention window using their weights. For this method, we derive a multihop packet collision model. The proposed scheme is fully distributed and does not require any global information. Through an extensive simulation study, we show that our scheme ensures per-node fairness without loss of the total aggregate throughput.

End-to-end mobility support in content centric networks

Content-centric networking CCN has been recently proposed as an alternative to traditional IP-based networking. In CCN, content is accessed by content name instead of a host identifier locational identifier. This new type of access methodology rapidly and efficiently disseminates content in combination with the in-network caching mechanism. For practical use of CCN, many network properties studied in IP-based networking are being revisited, and new types of CCN architecture components are being designed. Although mobility is an essential aspect of the future networking system, it has not been sufficiently studied. We therefore address fundamental mobility issues, such as seamless handover, optimal access point selection, network mobility, and handling of persistent interests. In addition, for each issue, we propose practical solutions that efficiently align to a CCN environment. To ensure seamless handoff, we propose various handoff schemes and compare their performance in terms of handoff latency using packet-level simulation. Because our proposed schemes are consistent with the characteristics and rules of CCN, we believe that they can easily be integrated as a part of CCN. Copyright

Efficient content delivery in mobile ad-hoc networks using CCN

Information-centric networking (ICN) is emerging as a future network technology. It has introduced the great advantage of information dissemination with low bandwidth consumption in wired testbed networks. Recently, ICN is also studied for mobile ad-hoc networks environments for efficient content distribution. In the existing works in the literature, broadcast delivery is actively utilized for designing new routing schemes since it seems well fitted to the nature of ICN conceptually. In this paper, we raise questions about this research direction by analysing the performance of reliability and energy efficiency of both broadcast and unicast delivery schemes. Our analysis shows that unicast delivery outperforms broadcast delivery, unless topological changes incur too much packet flooding overhead. Based on this observation, we present a novel energy efficient content distribution scheme that delivers the content in a unicast manner while minimizing flooding overhead by taking advantage of ICN features. Via ns-3 simulation, we compare the performance of the proposed scheme with that of other comparative schemes, and show that the proposed scheme achieves much higher reliability and energy efficiency in content distribution under mobile ad-hoc network environments.

Enhanced cooperative communication MAC for mobile wireless networks

In this paper, we propose a new MAC (medium access control) protocol called enhanced cooperative communication MAC (ECCMAC) based on IEEE 802.11. The major objective of ECCMAC is to maximize the benefits of cooperative communication. We first propose a scheme for selecting and maintaining the best relay node. Second, since both cooperative communication and network coding rely on the selection of a relay node, we consider exploiting a network coding technique for additional throughput improvement. Third, to accommodate asymmetric link rates between a sender and a relay node, we employ ECCMAC to measure forward and reverse link rates, whereas prior works have simply assumed symmetric rates. ECCMAC is evaluated in this paper through theoretical analysis, extensive simulation, and simulation with measured data, and the results show that ECCMAC effectively improves wireless network performance.