Bird C. Lo

HOPSMAN: An Experimental Testbed System for a 10-Gb/s Optical Packet-Switched WDM Metro Ring Network

For future WDM MANs, optical packet-switching has been considered to be a promising paradigm that efficiently supports a wide range of Internet-based applications having time-varying and high bandwidth demands and stringent delay requirements. This article presents the design of an experimental testbed system for a high-performance optical packet-switched WDM metro ring network, HOPSMAN. HOPSMAN boasts three crucial features. First, it has a scalable architecture in which the number of nodes is unconstrained by the number of wavelengths. Second, HOPSMAN nodes are equipped with high-speed photonic hardware components, including fast tunable receivers and optical slot erasers, capable of performing speedy optical packet-switching operations. Third, HOPSMAN incorporates a MAC scheme that embodies efficient and dynamic bandwidth allocation, resulting in exceptional delay-throughput performance. The article presents the key hardware components by highlighting the challenging issues we faced and the solutions we proposed for the testbed implementation. Finally, to demonstrate the feasibility of HOPSMAN, the article describes the experimental setup and presents the results obtained from running a commercially available remote media player application on the system.

A High-Performance Optical Access and Control System for Packet-Switched WDM Metro Ring Networks

In this paper, we present the access and control design of a high-performance optical packet-switched WDM metro ring network (HOPSMAN). HOPSMAN has been designed for networks and nodes to be unconstrained by the number of wavelengths. It includes a handful of nodes that are equipped with fast optical slot erasers making bandwidth reusable and achieving greater bandwidth efficiency. In essence, HOPSMAN incorporates a versatile medium access control (MAC) scheme, which embodies efficient and fair bandwidth allocation in accordance with a quota being exerted probabilistically. The quota is analytically derived with the number of slot-eraser-nodes taken into account. The scheme also employs a new notion of credit to regulate flexible access of remaining bandwidth that is suitable for the metro environment with bursty traffic. With the MAC scheme, HOPSMAN is shown to achieve exceptional throughput, delay, and fairness performance under a wide range of traffic settings via simulation results.

Hexanary-feedback contention access with PDF-based multiuser estimation for wireless access networks

Most existing contention access schemes are inherently unstable resulting in exponentially deteriorating throughput under increased traffic loads. In this paper, we propose a wide-sense stable (WSS) efficient hexanary-feedback contention access (HFCA) scheme, capable of providing signaling traffic high performance while retaining maximal throughput for wireless access networks. HFCA performs incremental contention resolution, managing a small subset of users at a time via a two-phase process. In the first phase, a group of users is probabilistically admitted, with a negligible probability of the group size greater than five. In the second phase, all users in the group are efficiently resolved. The two-phase process is augmented with hexanary feedback control facilitated by a probability density function (pdf)-based multiuser estimator (PMER) implemented at the physical layer. Basically, PMER measures the exact number of transmitting users (zero to five) in a contention slot by matching the envelope-phase pdfs histograms of received signals to a preconstructed pdfs library. To formally justify the performance of HFCA, we present throughput and stability analysis in which HFCA is shown WSS and the strict-sense stability condition is derived. Finally, analytic and simulation results delineate that, HFCA is highly robust against estimation discrepancy. Significantly, HFCA achieves high performance with respect to maximum stable and saturated throughputs, access delay, and blocking probability.

A synchronization paradigm with QoS guarantees for multimedia communications

We propose a synchronization paradigm, called SYNC*, offering two quality of service (QoS) requirements, skew and throughput, for multimedia communications, SYNC* is composed of three components: an intelligent video smoother (IVS), synchronizer, and multi-thread priority manager (MPM). While IVS and synchronizer achieves intramedia and intermedia synchronization, respectively, MPM ensures satisfactory throughput before playout. The main goal of the paper is to present in detail the design and performance analysis of the second component, the synchronizer. The synchronizer is aimed at achieving bounded skew between different media through periodic marking of correlated frames. The minimum marking interval yielding a given skew is analytically determined based on a Markov batch Bernoulli process (MBBP)/D/K/1 queueing model. We demonstrate the profound agreement between analytic and simulation results. The results also indicate that, the playout quality with respect to skew is highly relevant to the traffic burstiness and decoder buffer size. On the basis of a fixed marking interval, the greater the burstiness and buffer size, the poorer the playout quality.

A collision resolution paradigm for random access channel control in multi-access wireless networks

The random access channel (RACH) incurs a collision if more than one user make signaling requests over the same time slot, spreading code, or antenna element, in TDMA, CDMA, or SDMA wireless networks, respectively. We propose a hexanary-feedback collision resolution paradigm (HFCRP), capable of leveraging access efficiency of the RACH for all above wireless networks. HFCRP performs incremental contention resolution, managing a small subset of users at a time via a two-phase process. In the first phase, a group of users is probabilistically admitted, with a negligible probability of the group size greater than five. In the second phase, all users in the group are efficiently resolved. The two-phase process is augmented with hexanary feedback control facilitated by an envelope-PDF-based multi-user estimator (MR) implemented at the physical layer. Significantly, the MR measures the exact number of transmitting users (zero to five) in a contention slot by matching the envelope PDFs histograms of received signals to a library of pre-constructed PDFs. These six outcomes comprise the hexanary feedback being broadcast to users during the real-time operation of the two-phase process. Analytic and simulation results delineate that, performing in conjunction with the MR, HFCRP achieves high performance with respect to maximum stable throughput, saturated throughput, access delay, and blocking probability.

A perfectly stable contention access scheme for wireless access networks

Existing TDM-based contention access schemes exhibit the unstable or load-susceptible problem in which throughput exponentially deteriorates as the traffic offered load increases or fluctuates. In this paper, we propose a persistently stable, efficient hexanary-feedback-based contention access (HFCA) scheme, aiming to provide QoS guarantee while retaining stable and maximal network throughput. Unlike existing schemes that consider all contending mobile terminals as a whole, HFCA incrementally resolves a small group of terminals each time via a two-phase selection/resolution process. The incremental resolution repeats until the minimum non-blocking probability (QoS for signaling traffic) is satisfied. To accelerate resolution within the process, the number of simultaneously transmitting terminals is estimated based on an envelope-pdf-based estimator (EPER), by matching the corresponding normalized envelope histogram of the receiving signal with the priori envelope-pdf library. Facilitated with incremental resolution and the EPER, HFCA achieves the highest maximum throughput (0.574) and saturated throughput (0.52) reported to date irrespective of traffic increase and variation.

HOPSMAN: An Experimental Optical Packet-Switched Metro WDM Ring Network with High-Performance Medium Access Control

The paper presents the design and experimentation of a high-performance optical packet-switched metro WDM ring network (HOPSMAN). Equipped with novel medium access control, HOPSMAN achieves superior bandwidth efficiency, access delay, fairness, and bursty traffic adaptation.

An intelligent synchronization platform with QOS guarantees for multimedia communications

Quality of service (QOS) for diverse multimedia applications can be satisfied by the provision of synchronization platforms furnishing intramedia/intermedia synchronization and efficient process multitasking at end systems. As a result, the design of viable platforms should confront two concerns: network delay and jitter, and system multitasking. In this paper, we propose an intelligent synchronization platform, called SYNC*, satisfying given QOSs in terms of skew and throughput. SYNC* is composed of three components: intelligent video smoother (IVS), synchronizer, and multi-thread priority manager (MPM). While IVS and synchronizer deal with the network delay/jitter concern, MPM manages the challenge of system multitasking. We demonstrate via prototyping results that SYNC* achieves superior playout with respect to skew and throughput. We also observe that, the absence of either IVS/synchronizer or MPM results in unsatisfactory playout.

Wide-sense stable hexanary-feedback contention access for wireless networks

Most existing contention access schemes are inherently unstable resulting in exponentially deteriorating throughput under increased traffic loads. In this paper, we propose a wide-sense stable, efficient hexanary-feedback contention access (HFCA) scheme, capable of providing signaling traffic high performance while retaining maximal throughput for wireless access networks. HFCA performs incremental contention resolution via a two-phase process. The two-phase process is augmented with hexanary feedback control facilitated by a pdf-based multiuser estimator (PMER) implemented at the physical layer. We present throughput and stability analyses in which HFCA is shown wide-sense stable, and the strict-sense stability condition is derived. Finally, analytic and simulation results delineate that, HFCA achieves high performance with respect to maximum stable and saturated throughputs, access delay, and blocking probability.

A QoS-guaranteed MAC protocol using variable frame granularity for wireless access networks

In this paper, we propose a MAC protocol, called QMAC+, which adopts variable frame granularity, aiming to provide bandwidth-on-demand and QoS guarantees while retaining maximal network throughput. QMAC+ supports three traffic types-BR, VBR, and reservation request (RVR) for making CBR/VBR connection reservation. Essentially, QMAC+ governs weight-based reservation access (for VBR/CBR) and premier contention access (for RVR) over dynamically allocated reservation and premier contention bandwidths, respectively. In particular, the premier contention access performs incremental contention resolution by means of feedback control using an envelope-pdf-based estimator for the estimation of the number of concurrently transmitting users. As a result, the frame granularity is dynamically changed adapting to traffic fluctuations. Simulation results demonstrate that QMAC+ achieves superior performance with respect to throughput, delay, and blocking probability.