Te-Lung Liu

Performance of adaptive routing strategies in wavelength-routed networks

As the trend of increased reconfigurability emerges in wavelength division multiplexing (WDM) networks, lightpath establishment would be moved from static toward dynamic regimes. Therefore our interest is in real-time traffic where connection requests arrive dynamically and last for a random holding time if granted. We are concerned with the performance of adaptive routing algorithms in wavelength-routed networks with wavelength conversion capability. We first investigate several adaptive routing strategies, including the shortest path strategy, the least-loaded path strategy, and the proposed weighted-shortest path strategy . We then develop an analytical model to estimate blocking performance and compare the analyses with simulations. The numerical results show that the weighted-shortest path strategy can enhance blocking performance and fairly distribute load among the links.

Virtual LAN internetworking over ATM networks for mobile stations

One of the most attractive features of the virtual LAN (VLAN) is the capability to group users into broadcast domains, which are independent of their locations on the physical network. This paper deals with the VLAN services using ATM LAN emulation technology which operates on a client/server model. The focuses are on the issues of supporting transparent VLAN services and internetworking among VLANs for mobile stations. A mobile VLAN (MVLAN) architecture is proposed, perhaps for the first time, to efficiently maintain multiple VLAN broadcast domains over a single ATM network even when the VLANs contain mobile stations. The proposed solution (1) ensures that layer 2 frames between a mobile station and any station, either static or mobile, that belongs to the original registered VLAN can be exchanged transparently, (2) provides transparent communications between VLANs using the layer 2 bridging approach, and (3) handles excessive server-to-server traffic efficiently, including the broadcast/multicast frames. The proposed MVLAN architecture moves one step closer towards facilitating the mobility management in an ATM network while conforming to the emerging LAN emulation standard.

Mobility management of interconnected virtual LANs over ATM networks

One of the most powerful virtual LAN (VLAN) features is the capability to group users into broadcast domains, which are independent of their locations on the physical network. This paper deals with VLAN services using ATM LAN emulation technology which operates on a client/server model, and focuses on the issues of supporting transparent VLAN services for mobile terminals. A mobile VLAN architecture is proposed to efficiently maintain multiple VLAN broadcast domains over ATM networks even if the topology is changed dynamically due to mobility. This architecture exploits a hypercube over tree (HOT) hierarchical structure, i.e., trees are connected in a hypercube manner, to interconnect different VLANs servers. To filter excessive server-to-server traffic, an intelligent frame forwarding algorithm is proposed for the servers. The proposed mobile VLAN system brings us a step closer towards facilitating mobility and conforms to existing LAN emulation environment.

Dynamic traffic scheduling for QoS support in WDM/TDM networks with arbitrary tuning latencies

With the rapid growth of development of multimedia applications, the trend of accommodating a large variety of traffic with various quality-of-service (QoS) requirement has emerged. Optical networks based on wavelength division multiplexing (WDM) technology are capable of providing several terabits per second bandwidth; such attractive characteristics also makes WDM be considered as the most promising approach to achieve this goal. In order to efficiently exploit the extraordinary high bandwidth offered by optical fiber, WDM divides the bandwidth into a few wavelengths and there is no interference between transmissions on different wavelengths. Generally, there are two architectures, single-hop and multi-hop [17][18]. In a single-hop system, communications between a source node and a destination node complete in one hop. Conversely, in a multi-hop system, it is not necessary to satisfy the constraint of direct communication path; passing through one or more intermediate nodes is allowed.

Multicast routing for wavelength-routed WDM networks with dynamic membership

Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work, we explore the optical link control layer on the top of optical layer that enables the possibility of bandwidth on-demand service directly over wavelength division multiplexed (WDM) networks. Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks. Currently, it is difficult to provide wavelength multicast over the optical switches without optical/electronic conversions although the conversion takes extra cost. In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks. The goal is to joint a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as less as possible. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.

On the support of bandwidth on demand service over wide-area WDM optical networks

Future broadband networks must support integrated services and offer flexible bandwidth usage. Most existing proposals for wide-area wavelength division multiplexed (WDM) networks employ circuit switching adopting the concept of lightpath, in which each circuit or lightpath occupies an entire wavelength. This, however, is not suited for end-to-end transport of information streams, typically with each stream having its unique traffic characteristics such as the bandwidth needed, different traffic bursty nature, and diverse service requirements. In this paper, we explore the extensions of the functions of what we refer as the optical link control (OLC) layer, native on top of optical layer, to offer finer granularity of wavelength usage and further enable the possibility of bandwidth on-demand (BoD) service directly over WDM networks. The objective is to facilitate the support of integrated services over WDM networks and to mitigate the changes needed in the upper layers as well. The proposed approach attempts to exploit the strengths of both optics and electronics, in which packets are either routed end-to-end over a lightpath transparently, or forwarded from wavelength to wavclength by electronic switching, whenever required. Furthermore, in order to establish an end-to-end BoD connection, the issue of how to select the best wavelength to route the given connection is also investigated. The effectiveness of the proposal is evaluated by simulation.