Young-Joo Suh

An efficient multicast routing protocol in wireless mobile networks

Providing multicast service to mobile hosts in wireless mobile networking environments is difficult due to frequent changes of mobile host location and group membership. If a conventional multicast routing protocol is used in wireless mobile networks, several problems may be experienced since existing multicast routing protocols assume static hosts when they construct the multicast delivery tree. To overcome the problems, several multicast routing protocols for mobile hosts have been proposed. Although the protocols solve several problems inherent in multicast routing proposals for static hosts, they still have problems such as non-optimal delivery path, datagram duplication, overheads resulting from frequent reconstruction of a multicast tree, etc. In this paper, we summarize these problems of multicast routing protocols and propose an efficient multicast routing protocol based on IEFT mobile IP in wireless mobile networks. The proposed protocol introduces a multicast agent, where a mobile host receives a tunneled multicast datagram from a multicast agent located in a network close to it or directly from the multicast router in the current network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent may start multicast join process, which makes the multicast delivery route optimal. The proposed protocol reduces data delivery path length and decreases the amount of duplicate copies of multicast datagrams. We examined and compared the performance of the proposed protocol and existing protocols by simulation under various environments and we got an improved performance over the existing proposals.

Implementation and performance study of IEEE 802.21 in integrated IEEE 802.11/802.16e networks

In this paper, we propose a framework for the implementation of the IEEE 802.21 Media Independent Handover (MIH) standard and evaluate its performance through experiments in integrated 802.11/802.16e networks. The IEEE 802.21 standard defines three types of MIH services (event, command, and information) that facilitate the mobility management and handover process in heterogeneous networks. To support MIH services, we develop a MIH-capable mobile node and the MIH information service server. Then, we introduce the Connection Manager (CM) which utilizes MIH services. Two main roles of CM are supporting seamless vertical handovers and efficient access point (AP) discoveries. From the experimental results in the real test-bed, we can know that the MIH services can be used to reduce packet losses during a vertical handover and to reduce the AP discovery time and energy consumption of mobile nodes.

Software-based rerouting for fault-tolerant pipelined communication

This paper presents a software-based approach to fault-tolerant routing in networks using wormhole or virtual cut-through switching. When a message encounters a faulty output link, it is removed from the network by the local router and delivered to the messaging layer of the local nodes operating system. The message passing software can reroute this message, possibly along nonminimal paths. Alternatively, the message may be addressed to an intermediate node, which will forward the message to the destination. A message may encounter multiple faults and pass through multiple intermediate nodes. The proposed techniques are applicable to both obliviously and adaptively routed networks. The techniques are specifically targeted toward commercial multiprocessors where the mean time to repair (MTTR) is much smaller than the mean time between router failures (MTBF), i.e., it is sufficient to tolerate a maximum of three failures. This paper presents requirements for buffer management, deadlock freedom, and livelock freedom. Simulation results are presented to evaluate the degradation in latency and throughput as a function of the number and distribution of faults. There are several advantages of such an approach. Router designs are minimally impacted, and thus remain compact and fast. Only messages that encounter faulty components are affected, while the machine is ensured of continued operation until the faulty components can be replaced. The technique leverages existing network technology, and the concepts are portable across evolving switch and router designs. Therefore, we feel that the technique is a good candidate for incorporation into the next generation of multiprocessor networks.

All to-all communication with minimum start-up costs in 2D/3D tori and meshes

All-to-all communication patterns occur in many important parallel algorithms. This paper presents new algorithms for all-to-all communication patterns (all-to-all broadcast and all-to-all personalized exchange) for wormhole switched 2D/3D torus- and mesh-connected multiprocessors. The algorithms use message combining to minimize message start-ups at the expense of larger message sizes. The unique feature of these algorithms is that they are the first algorithms that we know of that operate in a bottom-up fashion rather than a recursive, top-down manner. For a 2/sup d//spl times/2/sup d/ torus or mesh, the algorithms for all-to-all personalized exchange have time complexity of O(2/sup 3d/). An important property of the algorithms is the O(d) time due to message start-ups, compared with O(2/sup d/) for current algorithms. This is particularly important for modern parallel architectures where the start-up cost of message transmissions still dominates, except for very large block sizes. Finally, the 2D algorithms for all-to-all personalized exchange are extended to O(2/sup 4d/) algorithms in a 2/sup d//spl times/2/sup d//spl times/2/sup d/3D torus or mesh. These algorithms also retain the important property of O(d) time due to message start-ups.

Design of Efficient Multicast Protocol for IEEE 802.11n WLANs and Cross-Layer Optimization for Scalable Video Streaming

The legacy multicasting over IEEE 802.11-based WLANs has two well-known problems-poor reliability and low-rate transmission. In the literature, various WLAN multicast protocols have been proposed in order to overcome these problems. Existing multicast protocols, however, are not so efficient when they are used combining with the frame aggregation scheme of IEEE 802.11n. In this paper, we propose a novel MAC-level multicast protocol for IEEE 802.11n, named Reliable and Efficient Multicast Protocol (REMP). To enhance the reliability and efficiency of multicast services in IEEE 802.11n WLANs, REMP enables selective retransmissions for erroneous multicast frames and efficient adjustments of the modulation and coding scheme (MCS). In addition, we propose an extension of REMP, named scalable REMP (S-REMP), for efficient delivery of scalable video over IEEE 802.11n WLANs. In S-REMP, different MCSs are assigned to different layers of scalable video to guarantee the minimal video quality to all users while providing a higher video quality to users exhibiting better channel conditions. Our simulation results show that REMP outperforms existing multicast protocols for normal multicast traffic and S-REMP offers improved performance for scalable video streaming.

All-to-all personalized communication in multidimensional torus and mesh networks

All-to-all personalized communication commonly occurs in many important parallel algorithms, such as FFT and matrix transpose. This paper presents new algorithms for all-to-all personalized communication or complete exchange in multidimensional torus- or mesh-connected multiprocessors. For an R/spl times/C torus or mesh where R/spl les/C, the proposed algorithms have time complexities of O(C) message startups and O(RC/sup 2/) message transmissions. The algorithms for three- or higher-dimensional tori or meshes follow a similar structure. Unlike other existing message-combining algorithms in which the number of nodes in each dimension should be a power-of-two and square, the proposed algorithms accommodate non-power-of-two tori or meshes where the number of nodes in each dimension need not be power-of-two and square. In addition, destinations remain fixed over a larger number of steps in the proposed algorithms, thus making them amenable to optimizations. Finally, the data structures used are simple, hence making substantial savings of message-rearrangement time.

Adaptive polling MAC schemes for IEEE 802.11 wireless LANs supporting voice‐over‐IP (VoIP) services

The IEEE 802.11 standard specifies the point coordination function (PCF) in the MAC sublayer for the transfer of real-time traffic, such as voice. The transfer of real-time traffic over wireless LANs is rapidly gaining acceptance, but little work has been done concerning the efficient use of IEEE 802.11 PCF mode to support voice services. In this paper, we propose adaptive polling MAC schemes for IEEE 802.11 PCF. Our proposed schemes reduce the polling overhead significantly, and provide efficient QoS guarantees as other polling protocols do. Our schemes use statistical behaviors of voice traffic sources to increase the performance of PCF mode. We analyze the applicability of our schemes to IEEE 802.11 WLANs and compare them with other related works.

Access router information protocol with FMIPv6 for efficient handovers and their implementations

Mobile IPv6, which is a protocol being standardized by IETF for global IP mobility support, is expected to play a key role for future all-IP wireless networks. As the demands for delay sensitive real-time applications increase, the handover latency of mobile IPv6 becomes inadequate for these applications. There have been many proposals, such as fast handovers for mobile IPv6 (FMIPv6), to tackle this problem. However, FMIPv6 only concentrates on the protocol operation while it does not address other issues, such as radio access discovery and candidate access router discovery, that are critical to the handover performance of FMIPv6. Therefore, in this paper, we propose ARIP (access router information protocol), which performs a candidate access router discovery and a radio access network discovery in one protocol suite, to provide an efficient handover framework for MIPv6 and FMIPv6. ARIP is designed to cope with heterogeneous networks as well as homogeneous networks and to be closely coupled with FMIPv6 to provide an efficient handover operation. The performance evaluation of MIPv6, FMIPv6, and FMIPv6 with ARIP is performed in an actual network environment and the performance results show that FMIPv6 with ARIP gives the best performance in terms of handover latency

Comparison of the underestimation rate in cases with ductal carcinoma in situ at ultrasound-guided core biopsy: 14-gauge automated core-needle biopsy vs 8- or 11-gauge vacuum-assisted biopsy

OBJECTIVE The objective of this study was to compare the underestimation rate of invasive carcinoma in cases with ductal carcinoma in situ (DCIS) at percutaneous ultrasound-guided core biopsies of breast lesions between 14-gauge automated core-needle biopsy (ACNB) and 8- or 11-gauge vacuum-assisted biopsy (VAB), and to determine the relationship between the lesion type (mass or microcalcification on radiological findings) and the DCIS underestimation rate. METHODS We retrospectively reviewed imaging-guided biopsies of breast lesions performed from February 2003 to August 2008. 194 lesions were diagnosed as DCIS at ultrasound-guided core biopsy: 138 lesions in 132 patients by 14-gauge ACNB, and 56 lesions in 56 patients by 8- or 11-gauge VAB. The histological results of the core biopsy samples were correlated with surgical specimens. The clinical and radiological findings were also reviewed. The histological DCIS underestimation rates were compared between the two groups and were analysed for differences according to the clinical and radiological characteristics of the lesions. RESULTS The DCIS underestimation rate was 47.8% (66/138) for 14-gauge ACNB and 16.1% (9/56) for VAB (p<0.001). According to the lesion type on sonography, DCIS underestimation was 43.4% (63/145) in masses (47.6% using ACNB and 15.8% using VAB; p=0.012) and 24.5% (12/49) in microcalcifications (50.0% using ACNB and 16.2% using VAB; p=0.047). CONCLUSION The underestimation rate of invasive carcinoma in cases with DCIS at ultrasound-guided core biopsies was significantly higher for ACNB than for VAB. Furthermore, this difference does not change according to the lesion type on ultrasound. Therefore, ultrasound-guided VAB can be a useful method for the diagnosis of DCIS lesions presented as either mass or microcalcification.

Performance comparison of mobile IPv6 and fast handovers for mobile IPv6 over wireless LANs

The increase of mobile devices is addressing a mobility support to facilitate handovers of mobile devices. Mobile IPv6 (MIPv6) has been proposed by IETF to solve this problem in the Internet. But, in MIPv6, there is a time interval that a mobile node (MN) cannot send or receive any packets during the handovers. The time interval is long enough for packets to be lost so that it is intolerable to be used for real-time traffics. Therefore, it is necessary to find out the method to reduce a handover latency. For this reason, Fast Handovers for Mobile IPv6 (FMIPv6) protocol has been proposed to reduce the MIPv6 handover latency. In FMIPv6, there are two operation modes due to the unpredictability of MNs mobility; the predictive mode and the reactive mode. In this paper, we discuss two modes of FMIPv6 and compare their performance with MIPv6 in a real test-bed network. The performance result shows that FMIPv6 has better handover performance than MIPv6 does. But, it also shows that FMIPv6 still suffers from the handover disruption time due to the IEEE 802.11 MAC layer handover. I. INTRODUCTION