Chunming Qiao

Integrated cellular and ad hoc relaying systems: iCAR

Integrated cellular and ad hoc relaying systems (iCAR) is a new wireless system architecture based on the integration of cellular and modern ad hoc relaying technologies. It addresses the congestion problem due to unbalanced traffic in a cellular system and provides interoperability for heterogeneous networks. The iCAR system can efficiently balance traffic loads between cells by using ad hoc relaying stations (ARS) to relay traffic from one cell to another dynamically. This not only increases the systems capacity cost effectively, but also reduces the transmission power for mobile hosts and extends system coverage. We compare the performance of the iCAR system with conventional cellular systems in terms of the call blocking/dropping probability, throughput, and signaling overhead via analysis and simulation. Our results show that with a limited number of ARSs and some increase in the signaling overhead (as well as hardware complexity), the call blocking/dropping probability in a congested cell and the overall system can be reduced.

QoS performance of optical burst switching in IP-over-WDM networks

We address the issue of how to provide basic quality of service (QoS) in optical burst-switched WDM networks with limited fiber delay lines (FDLs). Unlike existing buffer-based QoS schemes, the novel offset-time-based QoS scheme we study in this paper does not mandate any buffer for traffic isolation, but nevertheless can take advantage of FDLs to improve the QoS. This makes the proposed QoS scheme suitable for the next generation optical Internet. The offset times required for class isolation when making wavelength and FDL reservations are quantified, and the upper and lower bounds on the burst loss probability are analyzed. Simulations are also conducted to evaluate the QoS performance in terms of burst loss probability and queuing delay. We show that with limited FDLs, the offset-time-based QoS scheme can be very efficient in supporting basic QoS.

Optical burst switching: a new area in optical networking research

In this tutorial, we give an introduction to optical burst switching and compare it with other existing optical switching paradigms. Basic burst assembly algorithms and their effect on assembled burst traffic characteristics are described first. Then a brief review of the early work on burst transmission is provided, followed by a description of a prevailing protocol for OBS networks called just-enough-time (JET). Algorithms used as an OBS core node for burst scheduling as well as contention resolution strategies are presented next. Trade-offs between their performance and implementation complexities are discussed. Recent work on QoS support, IP/WDM multicast, TCP performance in OBS networks, and labeled OBS is also described, and several open issues are mentioned.

Assembling TCP/IP packets in optical burst switched networks

Optical burst switching (OBS) is a promising paradigm for the next-generation Internet infrastructure. We study the performance of TCP traffic in OBS networks and in particular, the effect of assembly algorithms on TCP traffic. We describe three assembly algorithms in this paper and compare them using the same TCP traffic input. The results show that the performance of the proposed adaptive-assembly-period (AAP) algorithm is better than that of the min-burstlength-max-assembly-period (MBMAP) algorithm and the fixed-assembly-period (FAP) algorithm in terms of goodput and data loss rate. The results also indicate that burst assembly mechanisms affect the behavior of TCP in that the assembled TCP traffic becomes smoother in the short term, and more suitable for transmission in optical networks.

A hybrid optical switching approach

Optical circuit switching (OCS) is a sophisticated technology widely deployed in current optical networks, and has many advantages in the transport of stable and long-duration traffic flows. However, it is not suitable for bursty data traffic. On the other hand, an alternative technology, optical burst switching (OBS), well addresses bursty IP traffic transport, but is not suitable for stable and large flows. To transport both types of traffic effectively, a hybrid optical switching approach is proposed which combines OCS and OBS to exploit the merits of both technologies. The performance has been evaluated in terms of throughput and blocking probability.

Proportional differentiation: a scalable QoS approach

The proportional service model has gained attention as an effective solution for quantitative service differentiation in IP networks. In particular, this differentiation scheme is controllable, consistent, and scalable. Thus, it gives network operators convenient management of services and resources even in a large-scale network. We give an overview of research efforts on this QoS model. Details about implementation strategies for various QoS metrics are provided. We also discuss how to achieve absolute service bounds in this relative differentiation model with different approaches. Several problems such as feasibility in differentiation are mentioned as open research issues at the end.

Schedule burst proactively for optical burst switched networks

Optical Burst Switching (OBS) is a promising paradigm for the next-generation Internet infrastructure. In OBS, a key problem is to schedule bursts on channels with both fast and bandwidth efficient algorithms so as to reduce burst loss. To date, most scheduling algorithms avoid burst contention locally (or reactively). In this paper, we propose several novel algorithms for scheduling bursts in OBS networks with and without wavelength conversion capability. The basic idea of our algorithms is to serialize the bursts on an outgoing link to reduce the number of bursts that may arrive at downstream nodes simultaneously (and thus pro-actively reduce the burst contention and burst loss probability at downstream nodes). This can be accomplished by judiciously delaying locally assembled bursts beyond a pre-determined offset time at an ingress node using the electronic memory. Compared with the existing algorithms, our proposed algorithms can significantly reduce the loss rate while ensuring that maximum delay of a burst does not exceed its prescribed limit.

Multilayer versus single-layer optical cross-connect architectures for waveband switching

Waveband switching (WBS) in conjunction with multigranular optical cross-connect (MG-OXC) architectures can reduce the cost and complexity of switching nodes. In this paper, we study two MG-OXC architectures: the single-layer and the multilayer MG-OXCs, and compare their performances with both off-line (static) and on-line (dynamic) traffic. In the off-line case, a near-optimal integer linear programming models (called off-ILP models) for each of the MG-OXC architectures aims to reduce the size of the MG-OXC, and compares them with the balanced path routing with heavy-traffic first waveband assignment (BPHT) heuristic developed for the multilayer MG-OXCs. The two architectures are then compared in terms of the number of wavelength a fixed number of wavelengths on each link. We also propose a novel efficient heuristic algorithm, called maximum overlap ratio (MOR) to satisfy new requests and compare it with the on-ILP, first-fit, and random-fit algorithms. We compare the two architectures in terms of the blocking probability, weighted (request) acceptance ratio, which serves as an indication of hops (WH) and MG-OXC ports required to satisfy a given set of traffic demands. In the on-line case, we develop an on-line ILP model called on-ILP, which aims to minimize the number of used ports for each of the MG-OXC architectures, given the revenue generated by satisfying the requests. Our results indicate that using WBS with either single-layer or multilayer MG-OXCs can reduce the number of ports (hence the size and cost) of the switching nodes compared to using ordinary OXCs (without waveband switching). In particular, in the off-line case, using single-layer MG-OXCs provides a greater reduction in size than multilayer MG-OXCs, while in the online case, using the multilayer MG-OXC is better

Synchronous optical burst switching

We introduce a new protocol based on the optical-burst-switched (OBS) transport to support synchronous services such as SONET/SDH. We term this protocol synchronous optical burst switching (SOBS) and describe the problems and challenges of supporting both synchronous and asynchronous traffic with various bandwidth granularities. We discuss the problems of path signaling, periodic reservations, and burst framing. We also highlight the importance of burst-level grooming, develop related analytical formulations, and present results of various simulations.

Performance comparison of OBS and SONET in metropolitan ring networks

This paper explores the feasibility of deploying optical burst switching (OBS) in metropolitan area networks (MANs) as an alternative to synchronous optical network (SONET), over wavelength-division multiplexing. We present a comparison between two OBS architectures (with centralized and distributed scheduling schemes), SONET, and next-generation SONET (NG-SONET), respectively. We quantify some of the performance metrics such as end-to-end delay and loss rate when supporting Ethernet traffic in metro ring networks. Our simulation results show that OBS offers significant performance improvement over SONET and NG-SONET. In general, the OBS architecture with distributed scheduling has a superior delay performance, whereas the OBS architecture with centralized scheduling has a better loss metric.