JaeSheung Shin

Mobility management alternatives for migration to mobile Internet session-based services

Session-based Internet protocol (IP) applications, such as Internet telephony, are an important component of the emerging mobile Internet. The ubiquitous availability of these services is critical to the success of the mobile Internet. Because all-IP networks will be deployed in phases and current mobile telecommunication systems will be in operation for decades to come, the interworking and migration between current network services and all-IP services is a key problem. In this paper, we address seamless roaming for session initiation protocol-based services across current cellular telecommunication networks and emerging all-IP wireless networks, such as those using third-generation and WiFi networks. We present an abstract mobility model, and map this model to three basic approaches for supporting seamless mobility: a master-slave approach, a federated system, and a unified approach. We discuss the challenges and implementation of an instance of the unified mobility management approach, called the Unified Mobility Manager, and then compare the tradeoffs of the three systems using a comparative performance analysis. We conclude that unified mobility management is most efficient if a great deal of interworking is required, and as more users invoke IP-based services; the federated approach is efficient when a single network technology is dominant and data access is limited, but requires sharing of data across networks; the master-slave approach is the least efficient, but is easy to introduce if the number of network types is small.

ASR: anonymous and secure reporting of traffic forwarding activity in mobile ad hoc networks

Nodes forward data on behalf of each other in mobile ad hoc networks. In a civilian application, nodes are assumed to be selfish and rational, i.e., they pursue their own self-interest. Hence, the ability to accurately measure traffic forwarding is critical to ensure proper network operation. These measurements are also often used to credit nodes based on their level of participation, or to detect loss. Past solutions employ neighbor monitoring and reporting on traffic forwarding of nodes. These methods are not applicable in civilian networks in which neighbor nodes lack the desire or ability to perform the monitoring function. Such environments occur frequently in which neighbor hosts are resource constrained, or in networks where directional antennas are used and reliable eavesdropping is difficult or impossible. In this article, we propose a protocol that uses nodes on the data path to securely produce packet-forwarding reports. Reporting nodes are chosen randomly and secretly so that malicious nodes cannot modify their behavior based upon the monitoring point. The integrity and authenticity of reports are preserved through the use of secure link layer acknowledgments and monitoring reports. The robustness of the reporting mechanism is strengthened by forwarding the report to multiple destinations (source and destination). We explore the security, cost, and accuracy of our protocol.

Multi-Hop Wireless Relay Networks of Mesh Clients

In typical deployments of infrastructure wireless mesh networks, mesh clients are directly connected to a mesh router. The mesh routers form a multi-hop wireless mesh backbone to provide connectivity to the Internet. In this paper, we propose and evaluate a set of distributed algorithms that enable mesh clients to form a multi-hop wireless relay network to have access to the mesh backbone. The proposed algorithms include path discovery, channel allocation, path selection, and local tuning of the resulting relay network. Results show that the performance of the relay network formed by our algorithms is very close to the optimal performance that the network can achieve.

Secure reporting of traffic forwarding activity in mobile ad hoc networks

Nodes forward data on behalf of each other in mobile ad hoc networks. In a civilian application, nodes are assumed to be selfish and rational, i.e., they pursue their own self-interest. Hence, the ability to accurately measure traffic forwarding is critical to ensure proper network operation. These measurements are often used to credit nodes based on their level of participation, or to detect loss. Past solutions employ neighbor monitoring and reporting on node forwarding traffic. These methods are not applicable in civilian networks where neighbor nodes lack the desire or ability to perform the monitoring function. Such environments occur frequently in which neighbor hosts are resource constrained, or in networks where directional antennas are used and reliable monitoring is difficult or impossible. In this paper, we propose a protocol that uses nodes on the data path to securely produce packet forwarding reports. Reporting nodes are chosen randomly and secretly so that malicious nodes cannot modify their behavior based upon the monitoring point. The integrity and authenticity of reports are preserved through the use of secure link layer acknowledgments and monitoring reports. The robustness of the reporting mechanism is strengthened by forwarding the report to multiple destinations (source and destination). We explore the security, cost, and accuracy of our protocol.

Relay-based Multi-hop Access to Wireless Mesh Networks

Wireless mesh networks are emerging as a means to provide ubiquitous network connectivity using various radio technologies. In this paper we propose and evaluate a set of distributed algorithms to form a multi-hop relay network to access the backbone in wireless mesh networks. The proposed algorithms include path discovery, frequency allocation, path selection, and local tuning of the resulting relay network. Our results show that the performance of the relay network formed by our algorithms is very close to the optimal performance that the network can achieve.

Channelization for Network Coding in Wireless Networks

Network coding is increasingly being investigated as an alternative to routing to increase throughput in packet networks. Like most data transfer schemes, the effectiveness of network coding may be limited by extreme congestion. When using network coding, these congested conditions are mitigated somewhat, but may still occur. We propose a selective channelization scheme in which links that experience congestion at a level that cannot be overcome by network coding are given reserved communication resources. This method has the following benefits. First, the algorithm proposed allows network coding full opportunity to overcome congestion before performing channelization, thus reducing the number of reserved resources used. Second, when triggered, the channelization of severely congested links greatly improves the end-to-end performance of flows that traverse the channelized link. To determine the point at which channelization should be triggered, we perform a thorough analysis of potential coding gains in a network facing errors due to collisions, and determine the point at which network coding loses its effectiveness.

Channelization for dynamic multi-frequency, multi-hop wireless cellular networks

Multi-hop relaying in cellular networks can greatly increase capacity and performance by exploiting the best available links to a base station. We envision an environment in which relay networks are dynamically formed when performance on the radio access network is degraded and then dissolved when the performance improves or the radio spectrum on which the relay network is operating is reclaimed. Each relay network operates on a different frequency band. Likewise, a relay network may channelize its frequency band to offer non-interfering links among the mobile nodes within a single relay network. We propose a set of algorithms used to form such relay networks on-demand. Each algorithm provides a simple and distributed frequency assignment scheme. We also propose two enhancements to improve network throughput of resulting relay networks. We evaluate these algorithms in terms of the overhead of the relay network formation. The evaluation results show that having nodes outmost from the BS initiate route discovery first is the best approach for reducing the formation overhead. The results also show that there is a large increase in throughput when using multiple frequencies in a relay network. Further, the performance of the network using multiple frequencies based on our simple frequency assignment is very close to that of a network using optimal frequency assignment.

Accurate hybrid mode analysis of hollow optical fibers

The dispersion relation equation of hybrid modes in hollow optical fiber is derived in the closed form by modeling the fiber in a three-layered structure and by rigorous hybrid mode analysis. The effective refractive indices of hybrid modes as a function of wavelength are accurately calculated. Modal characteristics and transverse field distributions of hollow optical fiber are precisely analyzed by use of the derived hybrid mode dispersion relation equation and the compact 2-D finite difference time domain method. In addition, the effects of the fiber dimension on propagating properties are presented. The number of hybrid modes that can exist in hollow optical fiber is calculated as a function of fiber dimension. We believe that this rigorous analysis is very accurate and provides precise computing methods to design and characterize hollow optical fiber based optical devices.

On-demand diversity wireless relay networks

There has been much recent attention on using wireless relay networks to forward data from mobile nodes to a base station. This network architecture is motivated by performance improvements obtained by leveraging the highest quality links to a base station for data transfer. With the advent of agile radios it is possible to improve the performance of relay networks through intelligent frequency assignments. First, it is beneficial if the links of the relay network are orthogonal with respect to each other so that simultaneous transmission on all links is possible. Second, diversity can be added to hops in the relay network to reduce error rates. In this paper we present algorithms for forming such relay networks dynamically. The formation algorithms support intelligent frequency assignments and diversity setup. Our results show that algorithms that order the sequence in which nodes join a relay network carefully, achieve the highest amount of diversity and hence best performance.

Analysis of hollow optical fiber couplers using the compact two-dimensional finite-difference time-domain method

The coupling characteristics of newly proposed hollow optical fiber (HOF) couplers are rigorously analyzed using the compact 2-D finite-difference time-domain (FDTD) method. The FDTD-simulated coupling efficiency as a function of the coupling length, and the transverse electric field distributions of the higher-order mode converted by the HOF couplers, are investigated. We propose that the designed HOF couplers can be used for various optical devices such as side-pumping double-clad fibers, mode splitters, and power monitors.