Wei-Kuo Chiang

The ( n,k )-star graph: a generalized star graph

The objective of this paper is to propose a new topology, called the (n,k)-star graph, such that it removes the restriction of the number of nodes n! in the n-star graph, and preserves many attractive properties of the n-star graph, such as node symmetry, hierarchical structure, maximal fault tolerance and simple shortest routing.

On the arrangement graph

Abstract The arrangement graph was proposed as a generalization of the star graph topology. In this paper we investigate the topological properties of the (n, k)-arrangement graph An,k. It has been shown that the (n, n − 2)-arrangement graph An,n − 2 is isomorphic to the n-alternating group graph AGn. In addition, the exact value of average distance of An,k has been derived.

TOPOLOGICAL PROPERTIES OF THE (n,k)-STAR GRAPH

The star graph, though an attractive alternative to the hypercube, has a major drawback in that the number of nodes for an n-star graph must be n!, and thus considerably limits the choice of the number of nodes in the graph. In order to alleviate this drawback, the arrangement graph was recently proposed as a generalization of the star graph topology. The arrangement graph provides more flexibility than the star graph in choosing the number of nodes, but the degree of the resulting network may be very high. To overcome that disadvantage, this paper presents another generalization of the star graph, called the (n,k)-star graph. We examine some topological properties of the (n,k)-star graph from the graph-theory point of view. It is shown that two different types of edges in the (n,k)-star prevent it from being edge-symmetric, but edges in each class are essentially symmetric with respect to each other. Also, the diameter and the exact average distance of the (n,k)-star graph are derived. In addition, the fault-diameter for the (n,k)-star graph is shown to be at most the fault-free diameter plus three.

Topological properties of hierarchical cubic networks

Abstract The hierarchical cubic network (HCN), which takes hypercubes as basic clusters, was first introduced in [6]. Compared with the hypercube of the same size, the HCN requires only about half the number of links and provides a lower diameter. This paper first proposes a shortest-path routing algorithm and an optimal broadcasting algorithm for the HCN. We then show that the HCN is optimal fault tolerant by constructing node-disjoint paths between any two nodes, and demonstrate that the HCN is Hamiltonian. Moreover, it is shown that the average dilation for hypercube emulation on the HCN is bounded by 2. This result guarantees that all the algorithms designed for the hypercube can be executed on the HCN with a small degradation in time performance.

Distributed fault-tolerant routing in Kautz networks

Abstract For a Kautz network with faulty components we propose a distributed fault-tolerant routing scheme, called DFTR, in which each nonfaulty node knows no more than the condition of its links and adjacent nodes. We construct a rooted tree for a given destination in the Kautz network, and use it to develop DFTR such that a faulty component will never be encountered more than once. In DFTR, each node is attempting to route a message via the shortest path. If a node detects a faulty node at the next hop, a best alternative path for routing the message around the faulty component is to be obtained. A best alternative path is first generated by the reduced concatenation of this node and the destination, and then is checked to make sure that it does not contain any of encountered faulty nodes. If it does, a new alternative path is generated as before. We invent an efficient approach in the checking step to reduce computational time. With a slight modification, DFTR may adapt to de Bruijn networks as well.

Network-Initiated Terminal Mobility in Voice over 3GPP-WLAN

This paper proposes a network-initiated terminal mobility mechanism (NITM) to facilitate handover with the session initiation protocol (SIP) in 3GPP Voice over WLAN (3GPP VoWLAN). We design the E2E tunnel state model running on the packet data gateway (PDG) using the CAMEL concept, and introduce the mobility server (MS) as a SIP application server to re-establish sessions with third party call control (3PCC). The MS is triggered to provide the terminal mobility service from the PDG by detecting the state transition of the E2E tunnel state model that represents the occurrence of a handover. This mechanism can advance the time to re-establish sessions. That is, our approach can provide smaller handover delay than mobileinitiated terminal mobility; moreover, it can handle mobility without additional support from the mobile host (MH). In addition, the handover missing problem (messages lost) might happen when the MH moves under communication. With the help of the MS, the lost messages are re-sent, and the handover missing problem, including simultaneous movement, is therefore solved.

Cross-layer handover for SIP applications based on media-independent pre-authentication with redirect tunneling

With the media-independent pre-authentication (MPA), a mobile node (MN) performs the pre-authentication and pre-configuration to get the new care-of-address (nCoA) as the layer 3 handover before the layer 2 handover, in order to lessen handover delay. However, in reality, the MN may perform the layer 2 handover due to the link going down before completing the layer 3 handover. It will cause the packet loss if there are packets destined to the MN with the old care-of-address (oCoA). To avoid packet loss, the MPA can be enhanced with redirect tunneling (RT), denoted by MPA-RT. Before performing the link layer handover, the MN would request the old access router (oAR) to create a redirect tunnel with the new access router (nAR) after deleting the proactive handover tunnel (PHT) that was built between the MN and the nAR. Then the oAR will forward data packets to the nAR via the redirect tunnel. The nAR also starts to buffer those packets until the MN completes the link layer handover, and flushes the packets to the MN. In addition, we integrate the MPA-RT with media independent handover (MIH) and session initiation protocol (SIP) to provide a seamless handover for SIP applications. Simulation results shows that the cross-layer handover can significantly reduce the packet transmission delay and the temporary packet buffer size, as compared with current alternatives.

IMS-Based Centralized Service Continuity

The IP Multimedia Subsystem (IMS) has been selected as a telecommunication industrial standard for the signal processing in the heterogeneous access networks. It is also brought up to handle the mobility management. However, the mobility of the user equipment (UE) may disrupt or even intermittently disconnect an ongoing real-time session, which heavily affects the satisfaction of the users. Therefore, how to reduce the service disruption time gets more and more important. This paper first proposes a centralized service continuity scheme, abbreviated as CSC, in IMS-based networks. The CSC treats handover as a service in the IMS network. Its architecture and operation are based on service invocation. The service continuity procedure is performed by an application server called CSC AS. The CSC AS can carry out the third-party call control for fast session re-establishment by initiating two INVITE requests concurrently. In addition, a variant of the CSC, denoted by CSC*, is derived by adopting the E-IMS AKA with one-pass authentication for achieving the acceleration of IMS registration during the handover. Analytical results show that both schemes could shorten the handover latency significantly, as compared with the standard IMS-based service continuity.

Integrating SIP-Based Network Mobility into IP Multimedia Subsystem

The combination of SIP-NEMO and IMS brings benefits of power saving, low complexity and few handoff to both end users and service providers. In this article we investigate the integration of SIP-NEMO in the IMS, and propose two interworking architectures: loosely coupled and tightly coupled. We also present three basic scenarios: registration, session establishment and optimized handoff with context transfer in the two architectures, respectively. The loosely coupled architecture maintains the original characteristics of SIP-NEMO and IMS. Control signals for the call setup are passed through the interrogating network in the IMS. The tightly coupled architecture utilizes the network agent of SIP-NEMO as a back-to-back user agent to integrate SIP-NEMO into IMS with minor modification of the IMS network and provides the security offered by IMS. The discussions on deployment and security issues show that the proposed approaches achieve the integration with minimal changes to the existing standards.

Simultaneous Handover Support for Mobile Networks on Vehicles

With high mobility rates of vehicles, there may be frequent occurrences of simultaneous handover. Our work focuses on and straightens out the problems resulting from simultaneous handover in SIP-NEMO. This article proposes a proxy-aided simultaneous handover (PASH) mechanism for the architecture of mobile networks operating on vehicles. The system architecture is modified from SIP-NEMO. We design a Fast Route/local routE re-Establishment (FREE) algorithm capable of re-establishing the optimized routing path fast and ensuring signaling messages buffered in local proxy could be sent to the correct destination without loss. Moreover, the Master- Slave Determination procedures derived from H.245 are introduced to handle the racing conditions fairly when two local proxies involved in a simultaneous handover issue re-INVITE requests at about the same time. Analytical results show that the handover delay can be improved significantly using the PASH, compared with the home-aided simultaneous handover.