Hui-Kai Su

An objective-oriented service model for VoIP overlay networks over DiffServ/MPLS networks

Bandwidth provisioning and QoS mapping are key issues to support multimedia services such as VoIP in the emerging network technologies. The classification feature enables MPLS (Multi-protocol Label Switch) to support differentiated types of services (DiffServ) with needed QoS. The differentiated service model provides a variety of mechanisms to achieve different objectives (such as call level or packet level satisfaction). To design a good service model, which can balance the call level and packet level QoS performances, is a challenging task. In this paper, we propose two objective-oriented service models for the VoIP services over the DiffServ/MPLS networks. They can be modeled as the continuous time Markov chains (CTMC) and the performance are assessed in details. The salient point for the proposed service models is to solve the myth of the trade-off between the service quality (users concern) and the system revenue (system providers concern) - involving how to meet each users SLA requirements while maximizing system revenue. The analytical results in this paper can provide useful information to both user and service provider for signing a cost-effective contract which provides a better trade-off between cost and QoS.

A hybrid indoor-position mechanism based on bluetooth and WiFi communications for smart mobile devices

With the development of embedded systems and the advance of communication network technologies, the positioning and creative value-added applications have been used widely. The global positioning system (GPS) cannot satisfy the requirements of indoor position applications. The GPS signals cannot be received in the indoor environment. Although the Wi-Fi position technologies are used for indoor location applications, the position accuracy is not accepted. Thus, this paper proposes a hybrid indoor-position mechanism based on Bluetooth and Wi-Fi communications. In the experiments, the position performance of using Wi-Fi and Bluetooth wireless signals with Neighboring Weighted Positioning method is better than that of using only Wi-Fi wireless signals. The average deviation of less than 5 meters and standard deviation of less than 2 meters.

Cooperative Power and Contention Control MAC Protocol in Multichannel Cognitive Radio Ad Hoc Networks

In this paper, we will propose a Cooperative Power and Contention control MAC (CPC-MAC) protocol in Cognitive Radio Ad Hoc Networks to solve the multichannel hidden terminal Primary User (PU) problem by build appropriate number of monitor nodes in suitable positions. There are two functions in this mechanism. First, secondary user (SU) transmitter sends the RTS frame including transmission power to SU receiver, SU receiver sends CTS frame including receiving power to SU sender. Monitor nodes send position and receiving power to SU sender and SU receiver. SU transmitter selects three monitors that their receiving powers are approach to each other. SU transmitter estimates its position and sending power by deterministic propagation model. This will reduce the interference to hidden PU terminal. Second, the SU in the transmission range of the PU will send one highest priority interrupt frame in control channel to one-hop SU neighbors to protect the PU. We also compare our proposed scheme to the existing IEEE 802.11 DCF and the other MAC protocols in Cognitive Radio ad hoc networks using ns2 simulation tool. We will show that CPC-MAC will improve the system throughput and reduce the energy consumption.

ASIC design of fast IP-lookup for next generation IP router

One of the prime designs for the next generation IP routers is the IP-lookup mechanism. The IP lookup has become a major performance bottleneck for the routers. In this paper, we propose a complete hardware architecture which includes searching, updating, inserting, and deleting functions. A simple hash hardware design is used to reduce the lookup time, and a CAM is also used to solve the collision problems effectively. The ASIC includes search unit, memory controller, 1M-byte cache and 3.18 Kbytes CAM for a 32000 entries routing table. The searching, updating and deleting functions only need 1 cycle and it is 96.88% to chance to hit the correct next hop in the first cycle.

A fast update scheme for TCAM-based IPv6 routing lookup architecture

With the rapid development of the Internet applications and the explosion of end users, IP address has been exhausted and routing lookup speed is the bottleneck of router design. In addition TCAM is widely used for implementation fast IP forwarding table lookup. However, the need to maintain a sorted list incremental updates may slow the lookup speed in a TCAM. In this paper, a fast TCAM update scheme is proposed for TCAM-Based IPv6 routing lookup architecture. Based on the characteristic of prefix distribution, we design a TCAM-Based router architecture for IPv6 routing lookup. As simulation result shows more than 90% update do not need any memory movement in updating operation. The worse case is (D-2)/2, where D is the length of chain.

IP Local Node Protection

Network survivability has become one of the most important QoS (quality of service) parameters in IP network services. IP protection can improve network resilience and avoid service disruption better than traditional routing recovery or other lower layer recovery technologies. In this paper, we proposed an IP local node-protection (IPLNP) scheme based on the characteristic of shortest path routing in IP networks. Our schemes working in an intra-area routing domain provide simple and efficient solutions to improve IP network survivability. Unlike source-routing-based MPLS (multiprotocol label switching) fast-reroute which needs an extra MPLS layer and complex control protocols, our scheme are applicable to a network employing only conventional IP routing and forwarding. Our scheme can prevent service disruption and packet loss caused by the loops which normally occur during the re-convergence of the network upon a failure. Because the backup next hops are predetermined in advance, the service interrupted time can be limited to a few milliseconds. In the simulation results, we observe that IP local node-protection scheme can efficiently improve network survivability while single node failure occurs.

A Local Fast-Reroute mechanism for single node or link protection in hop-by-hop routed networks

Network survivability has become one of the most important QoS (Quality of Service) parameters in IP network-based applications, particularly with regard to real-time multimedia applications. IP-based protection that enable recovery from failure in just a few milliseconds can provide greater network resilience than traditional routing recovery or other lower-layer recovery technologies. This paper proposes an IP protection scheme, called IP Local Fast-Reroute (IPLFRR), for single node or link protection. This scheme works in an intra-area routing domain, providing a simple and efficient solution to improve the survivability of IP networks. Unlike MPLS Fast-Reroute, which requires an extra MPLS layer and related protocols, the proposed scheme is applicable to a network employing conventional IP routing and forwarding. Moreover, our mechanism is capable of preventing service disruptions and packet loss caused by the transient loops that normally occur during reconvergence of the network following a failure. Because the backup next-hops are predetermined, service interruption can be limited to a few milliseconds, which is on par with the failure detection time. Simulation results show that IPLFRR is capable of improving network survivability, following the failure of a single node or link.

Design of Knowledge Management Learning System based on Service-Oriented Architecture

In this paper, we propose a framework of Knowledge Management Learning System (KMLS) for adult education based on a learning process and a Service- Oriented Architecture (SOA). Accordingly, this paper presents a case example to describe how to aid adult learning and making e-Learning more effective according to the principles of constructivism, knowledge management (KM) and the characteristics of adult learning and lifelong learning.

A Oneself Adjusts Backoff Mechanism for Channel Access in IEEE 802.11 DCF WLAN

In recent years, Wireless Local Area Networks (WLANs) are becoming more and more popular. The IEEE 802.11 protocol is one of the most widely deployed wireless access technologies. In order to minimize the collision probability due to multiple simultaneous transmissions, all stations compete for the wireless channel with a contention resolution method, namely the Binary Exponential Back off (BEB). In the BEB scheme, the contention window (CW) is doubled every time a station experiences transmission collision and decreases to its minimum value after a successful transmission. However, the performance degradation will be resulted from the aggressive reduction in the CW size. Accordingly, Exponential Increase Exponential Decrease (EIED) is proposed to suggest a slower reduction in a back off period after a successful transmission. Actually, the variation of CW causes unsteady system performance. In this paper, we proposed an Oneself Adjusts Back off (OAB) mechanism to improve system performance over contention-based Distributed Coordination Function (DCF) WLANs. In the OAB, the variation of CW state will be kept based on the number of the consecutive collision or successful transmission. The numerical results show that the OAB mechanism provides a better system throughput and collision rate than the related back off schemes.

An Integrated Two-Tier Multicast-Agent Architecture for All-IP Multicast Transport Services

Current group communication applications need to overcome inter-domain and heterogeneous multicast transport challenges. All-IP multicast over Internet is proposed to achieve the efficiency and transparency on IP multicast packet delivery not only for native IP multicast domains, but also for non-IP multicast supported domains. To guarantee the efficient IP multicast packet delivery over heterogeneous networks, therefore application level multicast (ALM) and overlay multicast (OM) were introduced for the connectivity of inter-domain coordination and local hetero-geneous access. In this paper, we propose two-tier multicast agent (MA) mechanism to integrate ALM with overlay tunnel connections to inter-domain multicast and network level connections to local heterogeneous multicast access. In our experimental results, the proposed MA mechanism can achieve all-IP multicast transport services with multicast packet transmission over inter-domain and heterogeneous local wired/wireless access networks.