一种基于OBGP协议的光网络域间路由的新型机制

本文提出一种采用光边界网关协议(OBGP)实现WDM光格状网的域间路由的新型机制;该机制基于最小跳选择策略建立最优化路径的思想,同时引进"迂回路由"策略和"并行信令"方式,实现了动态、分布式的光通道确立过程.在OPNet平台上针对两种网络拓扑进行仿真实验,结果表明:该机制能够在网络繁忙时期降低阻塞率,提高网络性能;同时发现:网络规模、单信道波长数以及网络负载等网络参数对于网络性能具有一定的影响.     

Signaling Schemes for Distributed Connection Management in Wavelength-Routed Optical Mesh Networks

The next-generation optical transport network will evolve from point-to-point connectivity to mesh networking, which can provide fast and automatic provisioning with enhanced flexibility and survivability. Signaling is used to support connection setup, maintenance, and teardown in such a network. In this paper, we study the performance of two hop-by-hop and one parallel signaling schemes in wavelength-routed optical mesh networks. Based on the sequence between optical crossconnect (OXC) switching and signaling message processing, we classify hop-by-hop signaling into two types that comply with the requirements of GMPLS signaling protocols. These two types are forward before switching configuration (FBSC) and forward after switching configuration (FASC). Also, we propose a parallel signaling scheme that is different from the existing hop-by-hop GMPLS signaling protocols. Considering OXC architectures and traffic patterns, we compare the FBSC, FASC, and parallel signaling schemes using simulation experiments, in terms of network blocking probability and reservation time. The simulation data reveal that the performance of a signaling scheme depends on the nature of the signaling as well as the network setting (e.g., the OXC architecture and traffic pattern). We analyze reasons for this result and discuss tradeoffs between these signaling schemes. This work offers some insight into designing an efficient signaling protocol for wavelength-routed optical mesh networks.     

An Efficient Distributed Control Scheme for Lightpath Establishment in Dynamic WDM Networks

An adaptive hybrid reservation protocol (AHRP) is proposed for the purpose of quickly and efficiently establishing a lightpath in dynamic wavelength routed networks. This protocol uses a special reservation-and-probe (RESV_PROB) packet and extends the signaling to integrate forward reservation and backward reservation into one monolithic process. To decrease the blocking probability that happens in cases where two end nodes associated with a specific link simultaneously reserve the same wavelength, an adaptive wavelength selection policy is specially employed in AHRP. A discrete-event simulation tool based on ns-2 is developed to investigate AHRP's performance, including its blocking probability, average lightpath setup delay, and signaling overhead. AHRP is also compared with existing protocols. Results show that during highly dynamic traffic conditions, AHRP possesses the lowest blocking probability, shorter setup delay, and less signaling overhead.     

自动交换光网络中恢复路径提供机制的研究

为了获得高效的网络生存性能,基于自动交换光网络(ASON)的框架,该文提出了一种新型的可恢复路径选择算法-联合可变权重可恢复路径(JVWR)选择算法,并进行了数值仿真分析,仿真结果表明,此恢复路径选择算法具有明显的业务量均衡能力,并降低了动态连接请求的阻塞概率,同时具有良好的带宽利用率和恢复资源共享效率。该文还对mesh网络业务路径和恢复路径的建立机制进行了讨论,在ASON功能框架之内,基于通用多协议标记交换提出了并行mesh共享恢复路径建立机制,从而较系统地对分布式恢复路径动态建立机制进行了研究。     

Spectrum-efficient optical drop-add-drop network with a centralized multi-carrier light source

Traditional ROADM networks strictly follow the coarse ITU-T standard wavelength grids and channel spacings, which would result in low optical spectrum utilizations under dynamic traffic requests of variable spectrum lightpaths. This paper presents a spectrum-efficient optical drop-add-drop network with a centralized multi-carrier light source (C-MCLS). The C-MCLS generates thousands of optical carriers with uniform and narrow channel spacings. The optical carriers are distributed to each network node as light sources on demand through ROADMs designed with the carrier-drop function. Spectrum-aware optical carrier allocation is studied first in the proposed network. This paper proposes a Minimum Fragmentation Request First (MinFragRF) optical carrier allocation algorithm compared with the Maximum Spectrum Request First (MaxSRF) and Minimum Spectrum Request First (MinSRF) allocation algorithms. This paper also studies how channel spacings of optical carriers impact on the network performance under variable traffic demands. We perform both network analysis and simulations to evaluate the network performance in terms of the lightpath blocking probability (LP_BP) and the effective spectrum efficiency. We analytically derive the formulas of LP_BP and average effective spectrum efficiency in the proposed network. Simulation results show that the proposed network with more narrow channel spacings greatly reduces the lightpath blocking probability compared with the traditional ROADM network. The average effective spectrum efficiency of the proposed network can be improved about 100 % compared with that of the traditional ROADM network by choosing appropriate network design parameters. The MinFragRF allocation algorithm has a better LP_BP performance than that of the MaxSRF and has a better spectrum utilization efficiency than that of the MinSRF. The optimal channel spacing evaluations show that narrow channel spacings such as 6.25 and 12.5 GHz greatly improve LP_BP performance when low bit-rate traffic requests dominate in the traffic model. However, as the high bit-rate traffic requests increase, the performance advantage of narrow channel spacings is gradually disappearing.     

An in-band signaling protocol for optical packet switching networks

Advances in optical networking reveal that all optical networks offering a multigigabit rate per wavelength will soon become economical as the underlying backbone in wide-area networks, in which the optical switch plays a central role. One of the central issues is the design of efficient signaling protocols which can support diversified traffic types, in particular the bursty IP traffic. This paper introduces a novel signaling protocol called the sampling probe algorithm (or SPA) to be used in a class of optical packet switching systems based on wavelength division multiplexing (WDM). The proposed scheme takes a drastically different approach from all existing signaling protocols. The salient features are 1) the pretransmission coordination is using an in-band signaling protocol, and thus does not require separate control channel(s) for transmission coordination; 2) the protocol is based on a reservation (connection) scheme which is capable of supporting multimedia traffic; 3) a gated service is adopted in which each successful reservation allows multiple packets (train of packets) to be transmitted, which can significantly reduce the per packet overhead; 4) the scheduling algorithm is adaptive by allowing flexible assignment of bandwidth on-demand; 5) the channel status gathering is done in a distributed fashion, and uses a passive listening mechanism, which itself does not interfere with packet transmissions. The results demonstrate that the proposed in-band signaling protocol can achieve high throughput and stability under heavy traffic condition.     

Label Preference Schemes for Lightpath Provisioning and Restoration in Distributed GMPLS Networks

In wavelength-routed networks based on a GMPLS control plane, the resource reservation protocol with traffic engineering extensions (RSVP-TE) allows to establish end-to-end lightpaths. The resource reservation can be blocked due to lack of available resources (forward blocking) or due to resource contentions (backward blocking). In wavelength-routed networks, the backward blocking is the predominant blocking contribution, when traffic load is low or highly-dynamic and when lightpath restoration takes place. To reduce the backward blocking, the paper proposes two label preference (LP) schemes compliant with RSVP-TE message exchanges. LP schemes provide the destination node with a label identifying the preferred wavelength to reserve. The preferred label is computed in a distributed way during the forward signaling phase, with the objective of assigning disjoint wavelengths to reservation attempts that may contend the resources. Simulation results demonstrate that, compared to other schemes, LP schemes are effective in reducing the backward blocking during both lightpath provisioning and restoration, without negatively impacting the forward blocking.     

Block Reservation Time Division Multiple Access (BRTDMA) Protocol for a High Capacity Wireless Network

Next generation high capacity wireless networks need to support various types of traffic, including voice, video and data, each of which have different Quality of Service (QoS) requirements for successful transmission. This paper presents an advanced reservation packet access protocol BRTDMA (Block Reservation Time Division Multiple Access) that can accommodate voice and data traffic with equal efficiency in a wireless network. The proposed BRTDMA protocol has been designed to operate in a dynamic fashion by allocating resources according to the QoS criteria of voice and data traffic. Most of the existing reservation protocols offers reservation to voice traffic while data packets are transmitted using contention mode. In this paper we propose a block reservation technique to reserve transmission slots for data traffic for a short duration, which minimizes the speech packet loss and reduce the end-to-end delay for wireless data traffic. The optimum block reservation length for data traffic has been studied in a cellular mobile radio environment using a simulation model. Simulation results show that the BRTDMA protocol offers higher traffic capacity than standard PRMA protocol for integrated voice and data traffic and offers flexibility in accommodating multimedia traffic.     

A non-competing hybrid optical burst switch architecture for QoS differentiation

In this paper, we present a new hybrid optical burst switch architecture (HOBS) that takes advantage of the pre-transmission idle time during lightpath establishment. In dynamic circuit switching (wavelength routing) networks, capacity is immediately hard-reserved upon the arrival of a setup message at a node, but it is used at least a round-trip time delay later. This waste of resources is significant in optical multi-gigabit networks and can be used to transmit traffic of a lower class of service in a non-competing way. The proposed hybrid OBS architecture, takes advantage of this idle time to transmit one-way optical bursts of a lower class of service, while high priority data explicitly requests and establishes end-to-end lightpaths. In the proposed scheme, the two control planes (two-way and one-way OBS reservation) are merged, in the sense that each SETUP message, used for the two-way lightpath establishment, is associated with one-way burst transmission and therefore it is modified to carry routing and overhead information for the one-way traffic as well. In this paper, we present the main architectural features of the proposed hybrid scheme and further we assess its performance by conducting simulation experiments on the NSF net backbone topology. The extensive network study revealed that the proposed hybrid architecture can achieve and sustain an adequate burst transmission rate with a finite worst case delay.     

Analysis of a dynamically wavelength-routed optical burst switchednetwork architecture

The concept of optical burst switching (OBS) aims to allow access to optical bandwidth in dense wavelength division multiplexed (DWDM) networks at fractions of the optical line rate to improve bandwidth utilization efficiency. This paper studies an alternative network architecture combining OBS with dynamic wavelength allocation under fast circuit switching to provide a scalable optical architecture with a guaranteed QoS in the presence of dynamic and bursty traffic loads. In the proposed architecture, all processing and buffering are concentrated at the network edge and bursts are routed over an optical transport core using dynamic wavelength assignment. It is assumed that there are no buffers or wavelength conversion in core nodes and that fast tuneable laser sources are used in the edge routers. This eliminates the forwarding bottleneck of electronic routers in DWDM networks for terabit-per-second throughput and guarantees forwarding with predefined delay at the edge and latency due only to propagation time in the core. The edge burst aggregation mechanisms are evaluated for a range of traffic statistics to identify their impact on the allowable burst lengths, required buffer size and achievable edge delays. Bandwidth utilization and wavelength reuse are introduced as new parameters characterizing the network performance in the case of dynamic wavelength allocation. Based on an analytical model, upper bounds for these parameters are derived to quantify the advantages of wavelength channel reuse, including the influence of the signaling round-trip time required for lightpath reservation. The results allow to quantify the operational gain achievable with fast wavelength switching compared to quasistatic wavelength-routed optical networks and can be applied to the design of future optical network architectures     

A Lagrangean relaxation based near-optimal algorithm for advance lightpath reservation in WDM networks

Advance lightpath reservation is a new research topic for connecting high-speed computer servers in lambda grid applications and for dynamic lightpath provisioning in the future optical internet. In such networks, users make call requests in advance to reserve network resources for communications. The challenge of the problem comes from how to jointly determine call admission control, lightpath routing, and wavelength assignment. In this paper, we propose an efficient Lagrangean relaxation (LGR) approach to resolve advance lightpath reservation for multi-wavelength optical networks. The task is first formulated as a combinatorial optimization problem in which the revenue from accepting call requests is to be maximized. The LGR approach performs constraint relaxation and derives an upper-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LGR approach employs a new heuristic algorithm to arrive at a near-optimal solution. By upper bounds, we assess the performance of LGR with respect to solution accuracy. We further draw comparisons between LGR and three heuristic algorithms—Greedy, First Come First Serve, and Deadline First, via experiments over the widely-used NSFNET network. Numerical results demonstrate that LGR outperforms the other three heuristic approaches in gaining more revenue by receiving more call requests.     

Experimental GMPLS-based provisioning for future all-optical DPRing-based MAN

Given the abundance and strategic importance of ring fiber plants in metropolitan area networks (MANs), and the accelerating growth of Internet traffic, it is crucial to extend the existing Internet protocol (IP)-based generalized multiprotocol label switching (GMPLS) framework to provision dynamic wavelength division multiplexing (WDM) optical rings. Nevertheless, the emerging GMPLS-based lightpath provisioning does not cover the intricacies of optical rings. No GMPLS standard exists for optical add-drop multiplexer (OADM) rings, relying instead upon proprietary static solution. The objective of this paper is to propose and evaluate novel GMPLS-based lightpath signaling and wavelength reservation schemes specifically designed for dedicated protection ring (DPRing)-based MANs. Performance evaluation has been carried out in a GMPLS-based testbed named ADRENALINE.     

Providing traffic tolerance in optical packet switching networks: a reinforcement learning approach

The servitization of network resources leads to new challenges for optical networks. For instance, to provide on-demand lightpaths as a service while keeping the probability of packet loss (PPL) low, issues such as lightpath setting up, resource reservation and load balancing must be addressed. We present a self-adaptive framework to process lightpath requests on packet switching optical networks that considers and handles the aforementioned issues. The framework is composed of a dimensioning phase that adds up new resources to an initial topology and a learning phase based on reinforcement learning that provides self-adaptation to tolerate traffic changes. The framework is tested on three realistic mesh topologies achieving a PPL between \(1 \times 10^{-1}\) and \(1 \times 10^{-6}\) for different traffic loads. Compared to fixed multi-path routing strategies, our framework reduces PPL between \(19\%\) and up to \(80\%\). Furthermore, no packet loss can also be achieved for traffic loads equal to or lower than 0.4.     

在IP/MPLS over WDM网络中基于准入机制的区分服务

在IP over WDM网络中,光层可以通过建立新的光路来为IP层提供带宽.如何利用光层有限的资源使网络服务提供商的利润最大化是流量疏导的一个重要目标.文章基于迭加网络模型,研究IP/MPLS over WDM网络的准入机制,设计算法在不影响整体效率的前提下为网络提供区分服务.     

Design and Performance Evaluation of a Separated Control Signaling Protocol for WDM Optical Networks

In WDM optical networks, an efficient control signaling protocol is required to dynamically establish lightpaths. This paper proposes a separated control signaling protocol (SCSP) and compares the performance of SCSP with a conventional integrated control signaling protocol (ICSP). The conventional ICSP makes reservations sequentially from the source to the destination for setting up and tearing down lightpaths. It increases the control overhead and wastes the network resource if it cannot reserve the network resource at an intermediate node. Specifically, if the receiver at the destination is not available after successful reservation at intermediate nodes, it wastes a lot of bandwidth. It causes decreasing chances of reservation for other lightpaths. Instead, SCSP separates bearer control from call control to reduce the waste of network resources. The call control function checks the availability of network resources such as wavelengths and receivers. Bearer control reserves, allocates, and releases network resources. To evaluate the performance of the two protocols, they are mathematically analyzed using a probabilistic model. Simulation results are also provided to compare the proposed protocol with the conventional ICSP in terms of utilization and blocking probability. From the results of simulation and iterative analysis, we can observe that SCSP performs better than ICSP.     

Virtual-topology adaptation for WDM mesh networks under dynamic traffic

We present a new approach to the virtual-topology reconfiguration problem for a wavelength-division-multiplexing- based optical wide-area mesh network under dynamic traffic demand. By utilizing the measured Internet backbone traffic characteristics, we propose an adaptation mechanism to follow the changes in traffic without a priori knowledge of the future traffic pattern. Our work differs from most previous studies on this subject which redesign the virtual topology according to an expected (or known) traffic pattern, and then modify the connectivity to reach the target topology. The key idea of our approach is to adapt the underlying optical connectivity by measuring the actual traffic load on lightpaths continuously (periodically based on a measurement period) and reacting promptly to the load imbalances caused by fluctuations on the traffic, by either adding or deleting one or more lightpath at a time. When a load imbalance is encountered, it is corrected either by tearing down a lightpath that is lightly loaded or by setting up a new lightpath when congestion occurs. We introduce high and low watermark parameters on lightpath loads to detect any over- or underutilized lightpath, and to trigger an adaptation step. We formulate an optimization problem which determines whether or not to add or delete lightpaths at the end of a measurement period, one lightpath at a time, as well as which lightpath to add or delete. This optimization problem turns out to be a mixed-integer linear program. Simulation experiments employing the adaptation algorithm on realistic network scenarios reveal interesting effects of the various system parameters (high and low watermarks, length of the measurement period, etc.). Specifically, we find that this method adapts very well to the changes in the offered traffic.     

WDM疏导网络中基于光路的动态恢复

针对波分复用(WDM)网络中单链路出错的生存性流量疏导问题,文章提出了一种基于光路的动态恢复机制(DRAL).DRAL不预留任何资源,当链路出错时,通过在网络中动态地发现资源来对错误链路进行恢复,将一个出错的光路转发到一条新建立的光路或其他可用的光路上.仿真结果显示,DRAL拥有很高的恢复概率.     

New signaling procedures in ATM networks for advance resource reservation

Currently, communication with resource reservation on ATM networks has been required by popularization of multimedia applications. Types of resource reservation are classified into two types according to reservation timing. One type invokes resource reservation just before communication between users. Another type invokes it in advance. In this type, resources can be reserved with communication time periods invoked by a user, well before actual communication. For the former type, several standardization committees, such as the ATM Forum and ITU‐T, have provided some signaling protocols. However, the latter type has no signaling protocol although necessity of this type has increased. This paper presents approaches of this type at first. Next, it proposes new signaling protocols to support this type keeping consistency with the conventional protocols for the former type, and compares proposed protocols. Moreover, it presents mechanisms to reserve resources cooperating with proposed signaling protocols. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optical resources provisioning: multipoint‐to‐point lightpaths mapping in all‐optical networks

In wavelength‐division multiplexing (WDM) optical networks, the bandwidth request of a traffic stream can be much lower than the capacity of a lightpath. Efficiently grooming low‐speed connections onto high‐capacity lightpaths will improve the network throughput and reduce the network cost. In this paper, we propose and evaluate a new concept of traffic aggregation in WDM mesh networks that aims to eliminate both the bandwidth under‐utilization and scalability concerns that are typical in all‐optical wavelength routed networks. This approach relies on the multipoint‐to‐point lightpath concept. In order to assess the efficiency of our proposal, all underlying network costs are compared. To achieve this aim, we devise a new provisioning algorithm to map the multipoint‐to‐point lightpaths in the network. Our results show that the proposed aggregation technique can significantly improve the network throughput while reducing its cost. Copyright © 2005 John Wiley & Sons, Ltd.