Jen-Yi Pan

DOCSIS performance analysis under high traffic conditions in the HFC networks

Hybrid Fiber Coaxial (HFC) networks provide a wide bandwidth and represent the solution of choice for many residential networks nowadays. The Data Over Cable Service Interface Specification (DOCSIS) protocol is an important standard for HFC networks and is supported by the majority of current vendors. This protocol uses the Truncated Binary Exponential Back-off (TBEB) algorithm to resolve collisions within the network by means of a back-off window. However, the performance of this algorithm tends to deteriorate when the network load is high. Consequently, the present study develops a novel mathematical model for the TBEB algorithm and then uses this model to identify the window size which yields the optimal system throughput and minimum delay time under high traffic conditions. The present numerical results confirm that the performance is improved when the window settings identified from the developed model are applied.

Multiple Care-of Addresses Registration and Capacity-Aware Preference on Multi-Rate Wireless Links

Users demand not only seamless continuation but also high throughput of Internet access as they hop across different administrative domains and heterogeneous networks during an ongoing session. By extending the multiple care-of addresses registration based on mobile IPv6, the proposed mechanism may provide seamless access with soft handoff notion as well as high throughput with automatically selecting the best link among multiple interfaces when the wireless channel continuously changes. Moreover, our mechanism can fit for any access technologies because only layer three modification and techniques (like packet pair) are required. The simulation result shows the proposed scheme outperforms the conventional mobile IPv6 in both seamless continuation and throughput. This study also provides a further insight on the issues of multiple interfaces and heterogeneous networks, which can promote the technology of next generation wireless network.

Context-aware service protocol. An extensible and configurable framework for user context awareness services in pervasive computing systems

A pervasive computing system has to be context-aware because it cannot distract users. However, users context information can be quite rich and unpredictable. Therefore, how to design an extensible protocol to achieve these requirements and implement a context-aware Internet service is very important. In this paper, we propose a SIP-compatible protocol for context-aware services, and this protocol is easy to understand, implement, and deploy. We also demonstrate some scenarios about this protocol to show transactions between client and server as well as behaviors of proxy/redirect servers. Finally, our projects implemented by this protocol are introduced. This study also provides a further insight on the issues of context-aware concept in pervasive computing, and demonstrates a referable methodology to propose and implement a context-aware framework in pervasive computing, which can promote the technology of future Internet.

Optimal bandwidth guaranteed routing and time slot assignment for broadband PLC access networks

High infrastructure availability, easy installation, and low device cost make PLC become one of the promising technologies for broadband communication. In PLC based access network, relay nodes are deployed to extend network coverage and enhance communication quality. In this paper, we consider the bandwidth guaranteed routing and time slot assignment problem in multi-hop PLC networks. Spatial reuse is considered in our system so multiple communication pairs can work at the same time if they do not interfere each other. In particular, our design takes channel quality into consideration in determining the optimal routing. Depending on the receiver node, the sender node uses the best modulation scheme to maximize transmission rate. We formulate the problem as an integer linear programming (ILP) problem. The objective is to minimize the time usage for total data delivery. The output includes optimal routing and collision free slot assignment for each node. To reduce the computation time, we propose a multi-section based algorithm to resolve the problem. We have carried out extensive numerical experiments on several network topologies. Numerical results reveal that the proposed approach obtains significant performance improvement on network resource usage compared to those without taking spatial reuse, routing, and rate adaptation into account.

Quality-aware SCTP in wireless networks

SCTP (Stream control transmission protocol) is a new transport layer protocol that was published as RFC2960 by IETF (the Internet Engineering Task Force) in October 2000 and amended in RFC4960 in September 2007. SCTP provides reliable ordered and unordered transport services. The congestion control and flow control mechanisms for SCTP are very similar to those for TCP (transmission control protocol). SCTP can apply more than one IP address when establishing associations. SCTP multihoming can support multiple paths in association. These features provide SCTP with some network-level fault tolerance through network address redundancy. SCTP multihoming has tremendous transmission potential. However, SCTP path management is very simple in RFC4960 and therefore cannot effectively distinguish path conditions; it also has no path switch strategy appropriate for wireless networking. These factors all degrade SCTP performance. This study proposes a new path management (quality-aware SCTP) for wireless networks; this includes a new path failure detection method and ICE (idle path congestion window size estimation) mechanism. An experiment using NS2 was performed, showing that quality-aware SCTP can effectively improve the network performance. Quality-aware SCTP is simple and provides a more effective performance than SCTP alone.

Throughput analysis of a novel backoff algorithm for IEEE 802.11 WLANs

The IEEE 802.11 medium access control (MAC) adopts binary exponential backoff (BEB) to provide a contention-based channel access mechanism in the wireless medium. But many researches have shown that BEB may deteriorate the performance when the number of stations increases. In this paper, we propose a new contention window (CW) control algorithm called TB (Tender Backoff) which can tenderly adjust the appropriate CW size. We will analyze the saturated throughput and compare TB with other backoff algorithms. The approach will be examined both by numerical analysis and simulation results. Furthermore, we also do a thorough analysis on the relationship between the CW size and throughput with the incremental amount of stations.

Vulnerability Assessment of IPv6 Websites to SQL Injection and Other Application Level Attacks

Given the proliferation of internet connected devices, IPv6 has been proposed to replace IPv4. Aside from providing a larger address space which can be assigned to internet enabled devices, it has been suggested that the IPv6 protocol offers increased security due to the fact that with the large number of addresses available, standard IP scanning attacks will no longer become feasible. However, given the interest in attacking organizations rather than individual devices, most initial points of entry onto an organizations network and their attendant devices are visible and reachable through web crawling techniques, and, therefore, attacks on the visible application layer may offer ways to compromise the overall network. In this evaluation, we provide a straightforward implementation of a web crawler in conjunction with a benign black box penetration testing system and analyze the ease at which SQL injection attacks can be carried out.

Improving R-score of Adaptive VoIP codec in IEEE 802.16 networks

Worldwide Interoperability for Microwave Access (WiMAX) technology, which is based on the IEEE 802.16 standard, supports different quality of service (QoS) for different services. WiMAX is expected to support QoS in real-time applications such as Voice over Internet Protocol (VoIP). When network congestion occurs, the VoIP bit rate needs to be adjusted to achieve the best speech quality. In this study, we propose a new scheme called Adaptive VoIP Level Coding (AVLC). This scheme takes into consideration network conditions (packet delay and packet loss) and a connection’s modulation scheme. The amount of data that can be transmitted increases with the speed of the modulation scheme. When network congestion occurs, AVLC scheme prioritizes reducing the bit rate of a connection that has a slower modulation scheme to mitigate congestion. Depending on network conditions, such as modulation scheme, packet delay, packet loss, and residual time slot, we use the G.722.2 codec to adjust each connection’s bit rate. Simulations are conducted to test the performance (network delay, packet loss, number of modulation symbols, and R-score) of the proposed scheme. The simulation results indicate that speech quality is improved by the use of AVLC.

A distributed multicast tree migration scheme for ATM based personal communication networks

A distributed multicast tree migration scheme for the ATM based personal communication networks is proposed. This distributed scheme automatically recognizes inefficient multicast trees and migrates them to better ones, if any. During the migration, the property of multicast services is also preserved and the data transmissions are synchronized. The performance of this scheme is evaluated via simulation, which shows that the proposed multicast tree migration scheme dramatically reduces the number of channels consumed per multicast tree. As a result, the number of successful established multicast trees is increased, the tree construction blocking rate is reduced significantly, and the diameters of multicast trees are kept as small as possible.

Hybrid Network Defense Model Based on Fuzzy Evaluation

With sustained and rapid developments in the field of information technology, the issue of network security has become increasingly prominent. The theme of this study is network data security, with the test subject being a classified and sensitive network laboratory that belongs to the academic network. The analysis is based on the deficiencies and potential risks of the networks existing defense technology, characteristics of cyber attacks, and network security technologies. Subsequently, a distributed network security architecture using the technology of an intrusion prevention system is designed and implemented. In this paper, first, the overall design approach is presented. This design is used as the basis to establish a network defense model, an improvement over the traditional single-technology model that addresses the latters inadequacies. Next, a distributed network security architecture is implemented, comprising a hybrid firewall, intrusion detection, virtual honeynet projects, and connectivity and interactivity between these three components. Finally, the proposed security system is tested. A statistical analysis of the test results verifies the feasibility and reliability of the proposed architecture. The findings of this study will potentially provide new ideas and stimuli for future designs of network security architecture.