Impairment constraint multicasting in translucent WDM networks: architecture, network design and multicasting routing

The popularity of broadband streaming applications requires communication networks to support high-performance multicasting at the optical layer. Suffering from transmission impairments in multi-hop all-optical (transparent) WDM multicasting networks, the signal may be degraded beyond the receivable margin at some multicast destinations. To guarantee the signal quality, we introduce a translucent WDM multicasting network to regenerate the degraded signals at some switching nodes with electronic 3R (reamplification, reshaping and retiming) functionality. The translucent network is built by employing three kinds of multicasting capable switching architectures: (1) all-optical multicasting capable cross connect (oMC-OXC), (2) electronic switch and (3) translucent multicasting capable cross connect (tMC-OXC). Among them both the electronic switch and tMC-OXC are capable of electronic 3R regeneration. Furthermore, we propose a multicast-capable nodes placement algorithm based on regeneration weight, and two multicasting routing algorithms called nearest hub first and nearest on tree hub first to provide signal-quality guaranteed routes for the multicasting requests. The numerical simulation on two typical mesh networks shows that it is sufficient to equip 30% of the nodes or less with signal-regeneration capability to guarantee the signal quality.     

Comparison of different congestion control strategies for low priority controllable traffic in packet switched backbone networks

It is expected that a significant part of the data flows of future multi‐service packet switched backbone networks will use low priority, non‐real‐time data transmission services of the networks. The common benefit for both user applications and network operators is that the data flows of the low priority services could use the free capacity of the networks, after the load of higher priority data flows. Congestion control methods are needed for these low priority data flows to reach an optimal utilisation level of the networks, high throughput and low packet loss ratios. This kind of low priority data transmission service which adjusts the data rates of the data flows according to the data rate changes of higher priority data flows, but does not guarantee any specific service for these data flows, is called a controlled load service. In this paper, we have compared the performance, efficiency and scalability of four different congestion control methods designed for the controlled load service. Two of these methods were based on very simple congestion control algorithms and the other two used relatively complex control algorithms based on control methods utilising computational intelligence. The principal aim of this study was to research how remarkable were the effects that the different complexities of the congestion control methods had on the achieved level of service. The simulation tests indicate that the complexity of the methods clearly affects the performance and efficiency of the methods. Copyright © 2001 John Wiley & Sons, Ltd.     

A performance study on optical burst switched networks: the ring topology

Existing performance studies on optical burst switched (OBS) networks have been focusing on channel blocking, i.e., when the required wavelength is not available on a link along a burst’s route. However, we identify another type of blocking as the receiver blocking, i.e., when the receiver at a burst’s destination node is occupied by another burst. Receiver blocking may account for the much larger part of total burst blocking. Receiver blocking has been largely ignored in existing research. In this paper we propose using multiple receivers or fiber delay lines (FDL) in front of the receivers in order to reduce the receiver blocking probability. Extensive simulation results on bi-directional OBS rings are presented to illustrate the problem and the performance of our proposed approaches. The results indicate that receiver blocking can be almost eliminated by using as little as three receivers and can be reduced by using a FDL of small length. To our knowledge, this is the first performance study that covers both channel and receiver blocking for OBS networks.     

Traffic models for slotted optical packet switched networks

Optical packet switching (OPS) has emerged as a promising architecture for the future all-optical network scenario. In order to have a successful deployment of OPS networks, several networking issues must be resolved, e.g., how to resolve contentions and how to provide Quality-of-Service (QoS) differentiation. Such networking studies often rely on teletraffic analysis in order to quantify the performance of the OPS network. In this paper, we introduce new and review existing traffic models for slotted buffer-less OPS networks. In particular, we present a novel asymmetric traffic model, suitable for studying the effects of non-uniform traffic. Optical packet switches with and without wavelength conversion are studied. Numerical evaluations and a comparison study of the presented traffic models are reported. The main contributions of this paper are to advance the field of establishing a theoretical framework for slotted OPS networks and to act as a tutorial for teletraffic engineering in such networks. http://www.item.ntnu.no/~haraldov.     

An effective buffering architecture for optical packet switching networks

A novel optical buffering architecture for Optical Packet Switching (OPS) networks is proposed in this article. The architecture which adopts a fiber-sharing mechanism aims at solving the problem of using a large number of fiber delay lines that are used to solve resource contention in the core node in OPS networks. The new architecture employs fewer fiber delay lines compared to other simple architectures, but can achieve the same performance. Simulation results and analysis show that the new architecture can decrease packet loss probability effectively and achieve reasonable performance in average packet delay.

QoS-oriented packet scheduling scheme for opportunistic networks

The unique characteristics of opportunistic networks (ONs), such as intermittent connectivity and limited network resources, makes it difficult to support quality of service (QoS) provisioning, particularly to guarantee delivery ratio and delivery delay. In this paper, we propose a QoS-oriented packet scheduling scheme (QPSS) to make decisions for bundle transmissions to satisfy the needs for the delivery ratio and delivery delay constraints of bundles. Different from prior works, a novel bundle classification method based on the reliability and latency requirements is utilized to decide the traffic class of bundles. A scheduling algorithm of traffic class and bundle redundancy is used to maintain a forwarding and dropping priority queue and allocate network resources in QPSS. Simulation results indicate that our scheme not only achieves a higher overall delivery ratio but also obtains an approximate 14% increase in terms of the amount of eligible bundles.     

Joint scheduling and power control supporting multicasting in wireless ad hoc networks

This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem.     

Keeping the packet sequence in optical packet-switched networks

This paper deals with optical packet switches with limited buffer capabilities, subject to asynchronous, variable-length packets and connection-oriented operation. The focus is put on buffer scheduling policies and queuing performance evaluation. In particular a combined use of the wavelength and time domain is exploited in order to obtain contention resolution algorithms that guarantee the sequence preservation of packets belonging to the same connection. Four simple algorithms for strict and loose packet sequence preservation are proposed. Their performance is studied and compared with previously proposed algorithms. Simulation results suggest that by accepting some additional processing effort it is possible to guarantee very low packet loss probabilities while avoiding the out-of-sequence delivery.     

XCP-based transmission control mechanism for optical packet switched networks with very small optical RAM

According to a famous rule-of-thumb, buffer size of each output link of a router should be set to bandwidth-delay product of the network, in order to achieve high utilization with TCP flows. However, ultra high speed of optical networks makes it very hard to satisfy this rule-of-thumb, especially with limited choices of buffering in the optical domain, because optical RAM is under research and it is not expected to have a large capacity, soon. In this article, we evaluate the performance of our explicit congestion control protocol-based architecture designed for very small Optical RAM-buffered optical packet switched wavelength division multiplexing networks with pacing at edge nodes in order to decrease the required buffer size at core nodes. By using a mesh topology and applying TCP traffic, we evaluate the optical buffer size requirements of this architecture and compare with a common proposal in the literature.

A new architectural approach for optical burst switching networks based on a common control channel

The new architectural approach to Optical Burst Switching networks presented here features a common control channel and a node locally maintained network model. The Common Control Channel allows for a fast and efficient broadcast of the network Control Packets, which in turn are used by every node to update its Local Network Model. The Local Network Model allows efficient network resource planning as each node is aware of the reservation status intentions for the resources on each node. This paper describes the new C³-OBS architecture, evaluates its comparative performance to regular OBS, assesses the manageable bandwidth for a C³-OBS network and evaluates the common control channel manageable load. The concept of “Well-Informed Node” is defined as a metric of trustfulness on the information managed by the Local Network Model and the scope and application of C³-OBS networks are studied.     

On a new multicasting approach in optical burst switched networks

We introduce a new multicasting approach, called tree-shared multicast (TS-MCAST), in order to alleviate overheads due to control packets and guard bands associated with data bursts when transporting multicast IP traffic in optical burst-switched WDM networks. We describe three tree sharing strategies and discuss implementation issues in constructing shared multicast trees for supporting TS-MCAST. Finally, we show the efficiency of TS-MCAST using simulation results.     

A flexible MAC protocol for the integration of high- and low-quality video streams, voice and data traffic over high-speed packet switched wireless networks

In this work, we propose and evaluate mechanisms for the multiplexing and the integrated delivery of various traffic types such as video, data and voice, over a wireless cellular high-speed packet switched network. Two different scenarios are examined where the video traffic results from videoconference sessions and high-quality media playback, respectively. In both cases we focus on the uplink channel and we thoroughly investigate, by using actual MPEG-4 video streams, the system's performance under a variety of possible loads. Our goal is to achieve high-aggregate channel throughput while preserving the quality of service requirements of each traffic type.     

ASON中共享路径保护机制的实现方法

研究了自动交换光网络(ASON)中,保护资源可部分共享的共享路径保护机制(Shared Path Protection,SPP)如何实现的问题.设计了该机制在符合波长连续性限制条件的WDM光网络中的路由计算算法及在ASON上实现该机制的信令流程.在ASON实验平台上实现了该机制.     

United stabilizing scheme for edge delay in optical burst switched networks

A novel scheme, namely united stabilizing scheme for edge delay, is introduced in optical burst switched networks. In the scheme, the limits of burst length and assembly time are both set according to certain qualifications. For executing the scheme, the conception for unit input bit rate is introduced to improve universality, and the assembly algorithm with a buffer safety space under the self-similar traffic model at each ingress edge router is proposed. Then, the components of burst and packet delay are concluded, and the equations that limits of burst length and assembly time should satisfy to stabilize the burst edge delay under different buffer offered loads are educed. The simulation results show that united stabilizing scheme stabilizes both burst and packet edge delay to a great extent when buffer offered load changes from 0.1 to 1, and the edge delay of burst and packet are near the limit values under larger offered load, respectively.     

Modeling and performance analysis of IP access interface in optical transmission networks with packet switching

The article analyzes the influence of the Internet Protocol (IP) access interface on the packet loss probability and delay times in the optical packet switched network. The network and node model have been proposed, and the structure of the IP access interface, including assembler and holder, have been included in the analysis. It has been shown that the increase of the maximum optical packet sizes, as well as use of the holding feature as contention resolution mechanism, decrease the packet loss probability, but introduce delays at the optical network access points. Modeling and analysis were based on the discrete event simulation assuming self-similar traffic sources. IP packet lengths were modeled using empirical data. This work has been conducted while the author was affiliated with the Telecommunication Laboratory, Swiss Federal Institute of Technology (EPFL-STI-ITOP-TCOM), Lausanne, Switzerland     

Addressing self-similarity in optical switching networks by means of ant colony optimization

In this work, we propose the use of an Ant Colony Optimization (ACO) algorithm to mitigate packet loss in an optical packet switching network that carries self-similar traffic, which is known to have a great impact in the buffer performance in terms of loss probability as exemplified in this work. By adaptively routing the packets and balancing the network load, we demonstrate by some simulations the effectiveness of this approach when compared with a shortest-path routing scheme, achieving a performance that is comparable to the Poisson traffic scenario in some cases. The proposed algorithm can be used as a viable alternative to traffic shaping techniques.     

利用FDL实现OBS网络中的组播业务

本文给出了一种OBS网络中组播业务的实现机制。它利用由光分路器和光纤延迟线（FDL）构成的组播功能模块实现了组播数据包在多分支节点处的复制、存储以及转发。仿真分析结果表明，该机制可以通过引入一定的时延，大幅降低丢包率。     

异步光分组交换网的流量建模

研究了异步光分组交换网的流量特性，提出了网络流量的解析模型和近似模型。研究表明，在采用计时门限光分组组装算法的情况下，如输入IP流具有短程相关特性(ShortRangeDependent)，则光分组的到达间隔时间呈负指数分布，光分组的长度趋于高斯分布。     

数据分组网中自相似业务模型的研究进展

本文介绍了数据分组网络中业务模型的研究进展。数据分组网络中，传统的泊松或马尔科夫模型在描述网络业务的精确性方面有很大的不足，近年来发展的自相似（单元形）业务模型效果较好。最近，研究人员在实测网络业务数据的基础上提出的多分形模型，不但能很好地模拟网络业务的长相关性，还能表现其在小的时间尺度下的特性。本文简单介绍了单分形业务模型，然后对多分形业务模型进行了重点的阐述，对业务模型的研究进展做出了分析。     

Performance analysis of an improved soft preemptive scheme for unevenly distributed traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be unevenly distributed across the network causing inefficient utilization of resources. To solve this problem, an improved soft preemptive (SP) scheme is proposed by considering dynamic resource distribution to deal with the uneven network utilization. A novel unevenly distributed traffic model in cross-time-zone networks is also presented to evaluate the efficiency of the new scheme. Compared with other schemes such as normal shortest path first (SPF) routing and wavelength conversion (WC), the new proposed scheme results demonstrate significantly better performance with respect to the network utilization and overall network blocking probability.