Wushao Wen

Signal-quality consideration for dynamic connection provisioning in all-optical wavelength-routed networks

We investigate new connection-provisioning algorithms to efficiently provide signal-quality-guaranteed connections in an all-optical WDM mesh network. In the all-optical network, signal degradations incurred by non-ideal transmission medium accumulate along a lightpath. When the signal degradation reaches a certain level, the connection is not usable and is blocked due to transmission impairments in the physical layer. To ensure high service quality of provisioned connections, it is essential to develop intelligent routing and wavelength assignment (RWA) algorithms which can combat the effects of impairments when setting up a connection. For this purpose, we propose two impairment-aware RWA algorithms, namely impairment-aware best-path (IABP) algorithm and impairment-aware first-fit (IAFF) algorithm. The optical signal-to-noise raito (OSNR) requirement and polarization mode dispersion (PMD) effect are used as signal-quality constraints to avoid setting up a connection with unacceptable quality due to the effects of transmission impairments. With the signal-quality consideration, as compared to algorithms that are not impairment aware in a realistic optical network, our proposed impairment-aware algorithms efficiently provide signal-quality-guaranteed connection while significantly reducing connection-blocking probability, better utilizing network resources, and having a reasonable computational requirement. Also, the effect of channel bit rate is studied in this paper.

LVMSR: an efficient algorithm to multicast layered video

Layered video is a video-compression technique to encode video data in multiple layers. It typically consists of a base layer and some additional layers that provide enhanced video quality. The multicasting operation of layered video consists of many receivers dynamically joining and leaving different multicast sessions of different layers depending on their network condition. A layered video multicasting system needs to satisfy: (i) bounded end-to-end delay from the video source to each receiver; (ii) minimum total cost; and (iii) minimum delay jitter between the various video streams received by each receiver. The problem of computing such data distribution paths is NP-complete. This paper presents a new heuristic algorithm, called layered video multicast super-tree routing algorithm, with O(Rn2) time complexity and O(R2) message complexity, where n is the number of nodes in the network and R is the receiver group size. Our investigation shows that the multicast data paths computed by our algorithm can always satisfy the delay constraint with reasonably low total cost.

A New Protection Model to Provide Availability-Guaranteed Service for Reliable Optical WDM Networks

Reliability is a crucial concern in high-speed optical networks. A service-level agreement (SLA), which mandates high service availability even in face of network failures, must be met in provisioning reliable connection. In this study, we investigate a generalized connection-provisioning and protection model to provide availability-guaranteed services in a wavelength-division multiplexing (WDM) optical mesh network. A novel link-state model is proposed to represent physical-layer availability and resource status for an optical link. This information can be used by a standard link-state routing protocol to efficiently provide reliable connections. In our proposed link-state-modeling mechanism, current network resource information and the physical components’ failure characteristics are aggregated to form a comprehensive dynamic link-state parameter, called link and resource availability (LRA). Based on such a dynamic link-state parameter, we also propose an algorithm for availability-guaranteed connection provisioning. A new generalized protection model is developed through our dynamic LRA-based provisioning. The dynamic LRA-based connection-provisioning algorithm efficiently provides SLA-guaranteed services while significantly improving connection reliability, better utilizing network resources, and achieving fast failure recovery.

Design and Analysis of a WDM Client/Server Network Architecture

In this article, we describe a novel wavelength-division multiplexing (WDM) client/server network architecture which is a passive-star-coupler-based, broadcast-and-select network. In this architecture, all down-stream data traffic uses WDM data channels and all upstream requests, upstream control messages, and down-stream control messages use an Ethernet channel (called the control channel). This architecture is broadcast and multicast capable. We describe a detailed point-to-point connection-setup procedure for this architecture. An internetworking scheme of this system with other networks is also described. The systems performance is analyzed in terms of whether the control channel or the data channels are the bottleneck. We also analyze the request delay, the requests channel-holding time, and the system throughput following the model description. The analysis shows that the control channel is not a bottleneck. When the user request rate is high, the server-channel scheduler is the most important adjustable factor to reduce the user response time. An illustrative analysis of FCFS scheduling policy for the system is also provided. Keywords: wavelength-division multiplexing (WDM); client/server network; bottleneck; scheduling; Ethernet; data channel; control channel; internetworking

Quality-of-service-based protection in MPLS control WDM mesh networks

Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality of service (QoS)-based protection in term of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and its impact to the sharing of their backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and fully automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration when deciding backup lightpaths. A simple analysis of the proposed algorithm in terms of computation, time, and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based sharing backup algorithms indicates that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network-resource utilization.

LVMSR-an efficient algorithm to multicast layered video

Layered video is a video compression technique to encode video data in multiple layers. It typically consists of a base layer and additional layers that provide enhanced video quality. The multicasting operation of a layered video may need to satisfy: (i) bounded end-to-end delay from a source to each receiver, (ii) minimum total cost, and (iii) minimum delay jitter between the various video streams received by the receivers. Because different nodes may request different video quality and because of limited bandwidth on the networks links, different layers of video data may reach their destinations over different distribution trees, and not all receivers may receive all of their requested layers. The problem of computing such data distribution paths is NP-complete, which means that no optimal solution method is available. This paper presents a new heuristic algorithm called LVMSR. With O(Rn/sup 2/) time complexity and O(R/sup 2/) message complexity, where n is the number of nodes in the network and R is the receiver group size. Our simulation results show that the multicast data paths computed by our algorithm can always satisfy the delay constraint with reasonably small total cost.

Design and analysis of a WDM client server network architecture

We propose a WDM client-server network architecture based on a passive-star-coupler-based broadcast-and-select network. In this architecture, all down-stream data traffic uses WDM data channels and all up-stream requests, up-stream control messages, and down-stream control messages use an Ethernet channel (control channel). This architecture is broadcast and multicast capable. We propose a detailed point-to-point connection-setup procedure for this architecture. The systems performance is analyzed in terms of whether the control channel or the data channels are the bottleneck. We also analyze the request delay, requests channel-holding time and system throughput following the model description. We conclude that the control channel is not a bottleneck in the system. When the user request rate is high, the server-channel scheduler is the most important adjustable factor to reduce the user response time. An illustrative analysis of FCFS scheduling policy for the system is provided.