业务光网络中光服务等级协定的研究

从业务光网络的角度对比服务等级协定(SLA)定义了光服务等级协定(O-SLA)的框架结构,在此基础上重点分析了O-SLA协商机制并提出一种动态协商的概念,对动态协商机制的实现流程进行了分析研究.随后总结了O-SLA得以有效实施的关键技术,并提出一种支持区分服务的O-SLA实施流程,此流程对于向端用户提供可定制化的光层业务提供了一种新思路.     

Full service optical access networks: ATM transport on passiveoptical networks

Multimedia communication has become the driving force for installing broadband systems in the public network. Different alternative solutions have been presented to realize a broadband interactive access network, such as installing optical fiber or upgrading the existing copper network with ADSL for twisted pair or hybrid fiber coax for CATV networks. Among these alternatives, optical fiber access networks are seen as the most future-safe solution. Especially, passive optical networks prove to be a cost-effective way to introduce fiber into the access network. This article presents ATM-based transport on passive optical networks, starting with a current implementation of an ATM-PON (APON) system that has already been installed for various trials. It further describes the evolution of APON systems to high-splitting, long-range PONs. The increase in both number of subscribers and distance range is discussed in combination with some specific technological issues such as upstream burst mode optical amplification. Special emphasis is placed on the work carried out within the scope of the ACTS PLANET project     

High availability path design in ring-based optical networks

This work develops mathematical models for path availability and provisioning resources required in various strategies for realizing high availability service paths in a transport environment of bidirectional line-switched rings or shared protection optical (wavelength division multiplexing) rings. The work originated in response to user requests for SONET service paths with unavailabilities under 30 s/year. A number of schemes for redundant routing and ring interconnection are considered as options to meet such a demanding target in the most economic way. An analytical framework for comparison of various provisioning schemes allows a “cost effectiveness” assessment of four high-performance alternatives, in terms of total resource investment and the corresponding service unavailability relative to a single-fed path construction. The logical models of cost and availability can be used in a variety of SONET or optical-ring transport planning studies or perhaps in future automated provisioning tools. An important finding is that while the availability benefit of dual-ring interconnection is high in metro-ring networks, the availability of paths through long-haul ring networks may be relatively poor due to lower limits from two-failure intra-ring combinations     

一种光网络中可用性的计算方法

光纤骨干通信网中,一条光纤的断裂会引起大量业务中断.因此,对于每一条工作光路可配置一条链路分离的保护光路.采用共享通路保护时光路连接的可用性计算是网络设计时的重要问题.现对共享通路保护方式下光路连接可用性的计算给出了推导过程和一种明显的计算公式.最后给出实例,通过与仿真结果的比较验证了计算方法的正确性.     

On management of CATV full service networks: a European perspective

The CATV network operators hope to offer digital services and evolve their networks to full service networks. There are many hurdles for them at the moment in the transition to a digital network and digital service offering from the current analog-based technology. Key to the success of the transition will be a well-integrated and capable management system to allow CATV operators and service providers to control the network as well as the services they will offer. The CATV operators need to agree on a common data communication infrastructure and plan how their new digital services will be offered to subscribers without disrupting the current customer base of analog service users. The choice of network technology and data communication protocols will have a strong influence on the network management technology chosen. A vital element for the provision of a common open communication architecture as well as for the purposes of network management is that the IP is used. The adoption of existing standards is vital in order to establish a fast route to open network management for CATV networks. It is possible that CATV operators and service providers will have to integrate existing SNMP management systems and TMN/OSI management, with newer integrated service management systems based on TINA and implemented on a CORBA platform. There is a strong need to address security issues before any of these technologies can be deployed for service. There is currently investment (deployed systems and research) which uses each of the technologies mentioned, so these technologies will need to coexist. This article highlights the differences between the North American and European network architectures, and outlines the European network and network management scenario. This is based on the authors involvement in a Pan-European CATV project, Integrated Broadband Communication over Broadcast Networks-IBCoBN     

A cost-based scheduling algorithm for differentiated service on WDM optical networks

One of the important issues in the design of future generation of high-speed networks is to provide differentiated services to different types of traffic with various time constraints. We propose an adaptive scheme to manage message transmission in single-hop passive-star coupler based wavelength-division multiplexing (WDM) optical networks. This study suggests that when scheduling message transmission in WDM networks a differentiated service should be considered in order to meet the time constraint to transmission of real-time messages while non real-time messages are being served so that the overall performance of the network could be improved.     

Survivable elastic optical networks: survey and perspective (invited)

Elastic optical networks (EONs) have been receiving extensive attention because of their inherent flexibility and the efficiency with which they allocate fiber-bandwidth. For an EON, survivability is of crucial importance because of the very high bandwidth that it carries on each optical channel. In this article, we review the current state of the art of survivable EONs which reviews the literature to summarize the following aspects: (a) spectrum resource sharing among backup lightpaths, (b) sharing of high-speed optical transponders, (c) effect of spectrum conversion, (d) bandwidth squeezed restoration (BSR), (e) joint restoration by multiple sub-band optical channels, (f) multi-layer survivability, and (g) energy efficiency. Apart from a summary on the current research status, we also discuss open research issues which are important to survivable EONs from the perspectives of (a) impact of spectrum conversion, (b) impact of elastic optical transponder configuration, (c) impact of physical layer impairments and limitations, (d) protection-path-based spectrum defragmentation, and (e) network availability.     

A generalized protection framework using a new link-State availability model for reliable optical networks

This paper investigates a generalized protection framework for availability-guaranteed connection provisioning in an optical wavelength-division-multiplexed (WDM) network. Reliability is a crucial concern in high-speed optical networks. A service level agreement (SLA), which mandates high service availability even in the face of network failures must be met in provisioning a reliable connection. In this study, a new link-state-modeling mechanism is developed to form a dynamic link-state parameter called link and resource availability (LRA), which represents physical-layer availability and resource status for an optical link. Such up-to-date link-state information can be used by a standard link-state routing protocol to efficiently provision reliable connections. Based on the link-state availability model, LRA, a connection-provisioning algorithm is then proposed which can guarantee customers' availability requirements. A new generalized protection model is developed through dynamic LRA-based provisioning. Numerical results demonstrate the performance of the proposed provisioning approach to be promising.     

A framework of scalable optical metropolitan networks for improvingsurvivability and class of service

The issues of scalability and class of service have been among the most important research focuses in design of the control plane for wavelength-routed WDM networks. We introduce a framework for achieving a scalable design in metropolitan area networks with WDM as the core technology (called optical metropolitan networks). The framework is summarized with the topics of survivability, scalability and class of service. A novel design concept, called interarrival planning, which aims to achieve scalable control and management in optical metropolitan networks, is addressed     

Time-dependent load-balancing service degradation in optical data center networks

Optical data center networks (ODCNs) are constructed by connecting geographically distributed data centers with optical networks. Due to the superiorities in computing and transmission performances, ODCNs have been widely acknowledged as a promising network paradigm to support the popular enterprise IT applications such as cloud computing and 3D rendering. However, the ever-increasing traffic burst and the expensive hardware upgrading impose more severe challenges on the design of resource allocation scheme in ODCNs, which is urgently required to take into account not only the service quality but also the economical profit of service provider. In this paper, we focus on the service degradation in ODCNs which has been proven efficient in reducing the denied requests in the overloaded network scenario by releasing portion of the occupied network resources with the acceptable service quality loss. Unlike the service degradation scheme in previous works, we first consider the impact of the time characteristics of service requests on the resource utilization and propose a novel time-dependent load-balancing service degradation (TD-LBSD) framework. In the TD-LBSD framework, a time-dependent link weight scheme is invented for the allocation of bandwidth resource to avoid the potential traffic congestion that is usually induced by the ignored dynamic nature of service requests. In order to support the high-level prepaid requests with unknown holding time, we also propose a statistical method to estimate the residual time of the occupied lightpaths based on the probability distribution of the holding time of past requests. Simulation results verified that our proposed service degradation framework outperforms the previous schemes with the profit gain of 6.2% and the reduced traffic congestions of 16.39% at best.     

The use of service level agreements in tactical military coalition force networks

Tactical military coalition force IP networks will have to offer quality of service. Service level agreements and service level specifications are important elements of the QoS architecture in civilian networks. However, SLAs/SLSs in military coalition networks should not be applied in the same fashion as in a commercial network. Our contribution is to identify the useful role SLAs/SLSs can play in network engineering and QoS management of tactical coalition force networks. The SLS definition needs to be more detailed than for a commercial SLS, and its monitoring must be performed on a finer timescale than in comparable commercial networks. The security architecture of military coalition networks may also restrict the monitoring and SLA management. Finally, we sketch a measurement-based approach showing how SLSs can be used in tactical military coalition force networks to support both call admission control and network engineering. Parts of this analysis include a discussion of SLSs and the proposed NATO standards for tactical communications network.     

Quality of service based protection in optical networks using diversity constraint

In this paper, we present a simple approach towards providing quality of service based partial protection in optical networks. We use a diversity based protection mechanism to ensure that in the event of link/node failures, a fraction of demand is always survived. To determine routing of optical paths while honoring restrictions such as wavelength continuity and exclusivity restriction, switching capability of OXCs, etc., we present a mixed-integer linear program formulation. Due to large size of the formulation, we develop an accompanied solution approach based on Lagrangian relaxation and sub-gradient optimization. We then present numerical results towards impact of diversity constraint upon the survivability, switch size, and number of carried wavelengths. Using them, we also show that optical networks based on sparse graphs might require higher number of wavelengths per fiber and the switching capacity of the OXCs to ensure higher values of fraction of accepted demands.     

Burst-cluster transmission: service differentiation mechanism for immediate reservation in optical burst switching networks

In this article we propose a service differentiated burst transmission called burst-cluster transmission to provide service differentiation in terms of burst loss for optical burst switching networks. The proposed method consists of a burst assembly algorithm and burst transmission scheduling, and it works only at the ingress edge node. A mixed timer/burst-length-based assembly algorithm is considered for burst assembly, and bursts with different service classes are assembled simultaneously according to the algorithm. A burst-cluster is generated so that the bursts in the cluster are arranged in order from lowest priority to highest. Then the burst-cluster is transmitted according to the burst transmission scheduling. We also consider the application of burst-cluster transmission to delay-sensitive traffic. We evaluate by simulation the performance of the burst-cluster transmission for NSFNET. Numerical examples show that burst-cluster transmission succeeds in providing different service grades even though the burst loss probabilities of high-priority service classes are affected by the traffic load of low-priority ones.     

Dynamic resource allocation with service guarantees over large scale optical networks

The lack of effective contention resolution mechanisms in the optical domain presents dynamic optical switching architectures with a hard dilemma between high loss (when adopting one-way reservations) and high delay (when using two-way reservations). In this work we evaluate an alternative hierarchical network architecture, which achieves a satisfactory compromise by partitioning the network into a number of geographically limited domains operating in slot and frame synchronous mode where two-way reservations are effective.     

Quality of service control in Ethernet passive optical networks based on virtual private LAN service technique

A technique is proposed that allows achievement of logical point-to-multipoint paths in gigabit Ethernet (GbE) networks with access based on passive optical networks (PONs), guaranteeing upstream/downstream bandwidth and quality of service also in conditions of traffic congestion. Such a method is based on the combination of the virtual private LAN service (VPLS), implemented in the core network, and the VLAN tagging forwarding process used in the edge-PON segment.     

Smooth upgrade of existing passive optical networks with spectral-shaping line-coding service overlay

A simple and cost-effective upgrade of existing passive optical networks (PONs) is proposed, which realizes service overlay by novel spectral-shaping line codes. A hierarchical coding procedure allows processing simplicity and achieves desired long-term spectral properties. Different code rates are supported, and the spectral shape can be properly tailored to adapt to different systems. The computation can be simplified by quantization of trigonometric functions. DC balance is achieved by passing the dc residual between processing windows. The proposed line codes tend to introduce bit transitions to avoid long consecutive identical bits and facilitate receiver clock recovery. Experiments demonstrate and compare several different optimized line codes. For a specific tolerable interference level, the optimal line code can easily be determined, which maximizes the data throughput. The service overlay using the line-coding technique leaves existing services and field-deployed fibers untouched but fully functional, providing a very flexible and economic way to upgrade existing PONs.     

The perspective of optical packet switching in IP dominant backboneand metropolitan networks

This article analyses the rationale and technical solutions for the use of optical packet switching techniques for both backbone and metropolitan applications. It also provides information on state-of-the-art technologies available for medium-term product development     

On service provisioning using light-trails in WDM optical networks with waveband switching

As the number of wavelengths in a single optical fiber increases, so does the number of ports needed for wavelength switching in optical cross-connects (OXCs), which may significantly increase the cost and difficulty associated with controlling large OXCs. Waveband switching (WBS) treats several wavelengths as a bundle that is switched through a single port if they share the same switch route, so that the number of ports needed can be reduced. On the other hand, light-trails in wavelength division multiplexing (WDM) optical networks allow intermediate nodes on established optical paths to access the data paths whereas light-paths only allow two end nodes to access the data paths. Therefore, light-trails offer significantly better flexibility for service provisioning and traffic grooming. In this article, we study service provisioning using light-trails in WDM optical networks with the WBS capability under a static traffic model. For comparison, integer linear programs are formulated for establishing light-trails with and without WBS. Numerical studies show that in certain cases, service provisioning with WBS in light-trail networks can reduce the number of ports needed while providing a more flexible sub-wavelength service provisioning capability. However, contrary to intuition, in most cases applying the WBS technique requires more ports in OXCs in light-trail networks. This study provides insights into the network design problem that applies the WBS technology to light-trail based optical networks.