Network performance and integrity enhancement with optical pathlayer technologies

Path layer technologies will play a key role in the development of a powerful and failure resilient B-ISDN. So far, they have been based on electrical technologies. This paper highlights WDM/FDM techniques and demonstrates that optical paths can greatly enhance the path layer capability and, therefore, the network performance. It is also shown that effective network failure restoration can be achieved with optical paths. The applicability of the wavelength path (WP) technique to global area networks is revealed by comparing different optical path realization techniques. WPs are applied to the national backbone network example to evaluate the required number of wavelengths, and to identify optical cross-connect node requirements. It then proposes a new optical path concept: the virtual wavelength path (VWP). In the VWP scheme, wavelengths are assigned on a link-by-link basis. In other words, the wavelength assigned to a wavelength path has only local significance. Significant benefits of the VWP such as the simplified path accommodation design within a transmission facility network and the reduced number of wavelengths needed, are elucidated. An optical cross-connect node architecture that enables the VWPs is also proposed. The architecture allows the VWP concept to be realized with commercially available optical technologies. The optical path layer concept proposed exploits and consolidates the layered transport network architecture and optical technologies, and will open up new opportunities for creating a B-ISDN that is bandwidth abundant and has a high degree of integrity     

Photonic transport network OAM technologies

The optical path concept was proposed to realize ubiquitous B-ISDN. It can make quantum leaps in both transmission capacity and cross-connect throughput simultaneously by exploiting WDM (wavelength division multiplexing) transmission and the wavelength routing capabilities of paths. Since the optical path is a new concept, new operation and management (OAM) systems and related technologies need to be developed before it can be fully utilized. This article discusses some of the key OAM-related issues and identifies the technical points necessary for future developments. The issues include optical path realization technologies, optical path accommodation design problems, a newly proposed optical transport network layer architecture, and the optical transport module for the network node interface     

OA&M framework for multiwavelength photonic transport networks

Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems     

Optical transport networks

The key technologies required for the development of optical transport networks, namely, optical fiber transmission and digital transport, which includes transmission signal multiplexing, transport nodes, and network operation functions, are highlighted. The trends in transport technology, the impact of synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM), the role of telecommunications management networks, and network integrity enhancement techniques are elucidated. It is demonstrated that these technologies have brought about a great change in transport network design and performance. Further innovations are required to fully realize a high-performance computer communication network, a cost-effective nationwide B-ISDN, and local networks for video distribution. These include the realization of an optical access transport network and the extension of trunk network capabilities which will be possible with optical path layer technologies     

All-optical four-fiber bidirectional line-switched ring

An all-optical four-fiber bidirectional line-switched ring (O-4F/BLSR) architecture is proposed. This new physical layer networking protocol uses wavelengths as tributaries and an optical supervisory channel to carry overhead information. Optical channels can be added and dropped from the ring, and virtual wavelength paths can be provisioned. Both node and link failures of a network can be protected through a two layer protection scheme. Protection switching within the optical multiplex section layer (OMS) restores failure caused by loss of optical continuity in a way similar to the SONET 4F/BLSR line switching. Protection switching within the optical channel layer restores single channel failure using 1:N protection. Test results show that the O-4F/BLSR can restore traffic in less than 50 ms. A self-healing, bandwidth efficient, and scalable all-optical transport network evolving from this O-4F/BLSR architecture is possible     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Approaches to optical Internet packet switching

Wavelength-division multiplexing is currently being deployed in telecommunications networks in order to satisfy the increased demand for capacity brought about by the explosion in Internet use. The most widely accepted network evolution prediction is via an extension of these initial predominantly point-to-point deployments, with limited system functionalities, into highly interconnected networks supporting circuit-switched paths. While current applications of WDM focus on relatively static usage of individual wavelength channels, optical switching technologies enable fast dynamic allocation of WDM channels. The challenge involves combining the advantages of these relatively coarse-grained WDM techniques with emerging optical switching capabilities to yield a high-throughput optical platform directly underpinning next-generation networks. One alternative longer-term strategy for network evolution employs optical packet switching, providing greater flexibility, functionality, and granularity. This article reviews progress on the definition of optical packet switching and routing networks capable of providing end-to-end optical paths and/or connectionless transport. To date the approaches proposed predominantly use fixed-duration optical packets with lower-bit-rate headers to facilitate processing at the network-node interfaces. Thus, the major advances toward the goal of developing an extensive optical packet-switched layer employing fixed-length packets are summarized, but initial concepts on the support of variable-length IP-like optical packets are also introduced. Particular strategies implementing the crucial optical buffering function at the switching nodes are described, motivated by the network functionalities required within the optical packet layer     

Optical burst switching: a viable solution for terabit IP backbone

Wavelength-division multiplexing has emerged as an important physical layer technology. Optical transmission provides a physical layer capable of carrying bits at the speed at the order of a gigabit per second. Optical burst switching is proposed to overcome the shortcomings of conventional WDM deployment, such as lack of fine bandwidth granularity in wavelength routing and electronic speed bottlenecks in SONET/SDH. We describe an architecture for IP network over the OBS WDM transmission core. The use of MPLS-type technique for forwarding data bursts and the inclusion of a medium access control layer between the optical (WDM) and IP layers are the key ingredients of the proposed architecture. In particular, the architecture is based on provisioning MPLS paths, also called label switched paths, of desired quality of service through the OBS WDM transmission core. The MAC layer performs various OBS-specific functions, such as burst assembly, burst scheduling, and offset setting/traffic shaping. While burst assembly and burst scheduling are relatively straightforward, we point out that the offset setting strategy has significant impact on the performance of IP network operating over OBS WDM core. We describe a shaping scheme to set the offset, an important system parameter for OBS, between the successive data bursts of a given data stream (label switched path) and their associated control packets. This scheme results in robust operation of the network and also facilitates traffic engineering. Guidelines are provided for implementing various IP QoS mechanisms in the optical backbone using OBS.     

Analysis and design for optical video transport distribution systemwith video on demand service

A cost-effective methods of multiplexing, transmitting, and selecting optical video signals is proposed and demonstrated by using appropriate combinations of bidirectional optical trunk-amplifier, medium-density wavelength division multiplexing (WDM) and optical space switching techniques for rapid cost-effective construction. The major factors affecting optical video transport/distribution system design are described. In particular, a tapping-type optical loop-shaped trunk section network is proposed from the viewpoint of system reliability, probability of call-loss, and B-ISDN with analog overlay. The experimental results and design philosophy for an optical selector composed of WDM filters and space switches connected by silica-based waveguide on a chip are also discussed     

Photonic transport network architecture and OA&M technologiesto create large-scale robust networks

In order to realize a large-scale and robust photonic transport network, a network protection strategy and operation, administration, and management (OA&M) realization scheme in wavelength division multiplexing optical path (WDM OP) transport networks has been developed. This paper discusses the networking (restoration/protection) concepts in each optical layer and proposes the most suitable networking strategy. To develop the OA&M technique, the characteristic information format of each optical layer must be discerned. A network node interface (NNI) structure for the WDM OP transport network is proposed. The proposed NNI is defined as the optical transport module (OTM). An OP signal format is defined as the optical transport unit (OTU). Overhead information and schemes to transmit it are also discussed     

Mini-slot TDM WDM optical networks

In recent years, optical transport networks have evolved from interconnected SONET/WDM ring networks to mesh-based optical WDM networks. Time-slot wavelength switching is to aggregate the lower rate traffic at the time-slot level into a wavelength in order to improve bandwidth utilization. With the advancement of fiber-optics technologies, continual increase of fiber bandwidth and number of wavelengths in each fiber, it is possible to divide a wavelength in a fiber into time-slots, and further divide a time-slot into mini-slots so that the fiber bandwidth can be more efficiently utilized. This article proposes a router architecture with an electronic system controller to support optical data transfer at the mini-slot(s) of a time-slot in a wavelength for each hop of a route. The proposed router architecture performs optical circuit switching and does not use any wavelength converter. Each node in the mini-slot TDM WDM optical network consists of the proposed router architecture. Three different network topologies are used to demonstrate the effectiveness and behavior of this type of network in terms of blocking probability and throughput.     

On Architecture and Limitation of Optical Multiprotocol Label Switching (MPLS) Networks Using Optical-Orthogonal-Code (OOC)/Wavelength Label

To accommodate the explosive packet-based data traffic in WDM networks, intelligent optical routing and switching are required in optical transport networks. Optical multiprotocol label switching networks emerged to meet this demand. In this paper, different schemes for implementing an OMPLS network are introduced. An optical MPLS network using OOC/wavelengths as labels is proposed. Based on an all-optical code converter, the architecture of the optical core router is demonstrated. The fundamental limits on scalability of the proposed core router, namely the label capacity, and the blocking probability of the label switched path setup are investigated, and closed-form solutions are derived.     

A management and visualization framework for reconfigurable WDM optical networks

As the phenomenal advance in optical WDM networking technologies continues, optical WDM network equipment has been deployed not only in backbone networks, but also in regional, metropolitan, and access networks. It is widely believed that a major component of the next-generation Internet will be an IP-based optical network employing WDM. WDM wavelength routing and signaling have become an active research field, and dynamic and adaptive wavelength routing and assignment algorithms have been proposed. However, there is less work on reporting network control and management system implementation efforts over testbed WDM networks. This article presents a network management and visualization framework aimed at guiding the development of management applications for reconfigurable WDM optical networks. A layered framework architecture including element and network management and visualization is provided, and an object-based information model representing the WDM network is introduced. Functional components on reconfiguration, software agent, and network visualization services are presented, and important issues related to optical lightpath generation are discussed. A network visualization service also provides WDM control and management APIs to applications and access networks such as an IP network management system. To illustrate the usage of the framework, we share our experience in implementing the MONET network control and management system, and present network visualization views obtained from the MONET WDM network to highlight the framework features.     

Architectures and technologies for high-speed optical data networks

Current optical networks are migrating to wavelength division multiplexing (WDM)-based fiber transport between traditional electronic multiplexers/demultiplexers, routers, and switches. Passive optical add-drop WDM networks have emerged but an optical data network that makes full use of the technologies of dynamic optical routing and switching exists only in experimental test-beds. This paper discusses architecture and technology issues for the design of high performance optical data networks with two classes of technologies, WDM and time division multiplexing (TDM). The WDM network architecture presented stresses WDM aware Internet protocol (IP), taking full advantage of optical reconfiguration, optical protection and restoration, traffic grooming to minimize electronics costs, and optical flow-switching for large transactions. Special attention is paid to the access network where innovative approaches to architecture may have a significant cost benefit. In the more distant future, ultrahigh-speed optical TDM networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over WDM networks. These advantages may include the ability to provide integrated services to high-end users, multiple quality-of-service (QoS) levels, and truly flexible bandwidth-on-demand. The paper gives an overview of an ultrahigh-speed TDM network architecture and describes recent key technology developments such as high-speed sources, switches, buffers, and rate converters     

Broad-band ATM network architecture based on virtual paths

Broadband transport techniques and network architectures based on the virtual path concept are examined. ATM (asynchronous transfer mode) techniques, when coupled with recent technological innovations, are expected to pave the way for future universal transport networks. The virtual path concept, which exploits the ATM's capabilities, is proposed to construct an efficient and economic network. The concept matches current and anticipated technological trends well. Characteristics and implementation techniques of virtual paths are discussed. Advantages of the virtual path concept and its impact on the transport network architecture are demonstrated. The virtual path strategy is also shown to provide efficiently for networks with dynamic reconfiguration capability which will enhance network performance. Some basic analytical results on the dynamic control effects of virtual paths are provided     

Architectural analysis of multiple fiber ring networks employingoptical paths

Analyzes the performance of various types of multiple fiber ring networks employing optical paths (OP's). The multiple fiber ring network architecture is suitable for achieving failure resilient networks that have extremely large bandwidth but are still upgradable against future increases in traffic. This architecture will overcome the limitation of conventional WDM rings in terms of network expansion capabilities, the number of nodes within the ring, and the number of OP's accommodated in the network. The generic node architecture suitable for multiple fiber ring networks is presented and functionality requirements are identified. The OP accommodation design algorithms that minimize the required node system scale are proposed. Based on the generic node architecture and proposed OP accommodation design algorithms, we evaluated the performance of several types of multiple fiber rings in terms of the required node system scale for rings under various conditions. The effect of the ring architecture (uni-/bidirectional rings), optical path schemes (wavelength path/virtual wavelength path), and different node connectivity patterns are demonstrated for the first time. The obtained results elucidate the criteria for selecting the most suitable multiple fiber ring architecture     

B-ISDN architecture and protocol

The authors discuss the architecture and protocol for broadband ISDN (B-ISDN) based on the CCITT standards. The discussion attempts to address the general concept of B-ISDN architecture and protocol and, whenever possible, present alternatives and the rationale for decisions in the selection of the protocol. B-ISDN is presented as a network evolution, and the impact of the asynchronous transfer mode (ATM) on the network is described. The role of virtual channel and virtual path in B-ISDN is discussed. The B-ISDN protocol structure and lower layer functions comprising the physical, ATM, and adaptation layers are presented, and the tentative trends of signaling and traffic control for the B-ISDN are delineated     

Logical topology design for IP rerouting: ASONs versus static OTNs

IP-based backbone networks are gradually moving to a network model consisting of high-speed routers that are flexibly interconnected by a mesh of light paths set up by an optical transport network that consists of wavelength division multiplexing (WDM) links and optical cross-connects. In such a model, the generalized MPLS protocol suite could provide the IP centric control plane component that will be used to deliver rapid and dynamic circuit provisioning of end-to-end optical light paths between the routers. This is called an automatic switched optical (transport) network (ASON). An ASON enables reconfiguration of the logical IP topology by setting up and tearing down light paths. This allows to up- or downgrade link capacities during a router failure to the capacities needed by the new routing of the affected traffic. Such survivability against (single) IP router failures is cost-effective, as capacity to the IP layer can be provided flexibly when necessary. We present and investigate a logical topology optimization problem that minimizes the total amount or cost of the needed resources (interfaces, wavelengths, WDM line-systems, amplifiers, etc.) in both the IP and the optical layer. A novel optimization aspect in this problem is the possibility, as a result of the ASON, to reuse the physical resources (like interface cards and WDM line-systems) over the different network states (the failure-free and all the router failure scenarios). We devised a simple optimization strategy to investigate the cost of the ASON approach and compare it with other schemes that survive single router failures.     

Strategy for protection and restoration of optical paths in WDM backbone networks for next-generation Internet infrastructures

This paper proposes and analyzes a strategy for protection and restoration of optical paths in wavelength division multiplexing (WDM) networks for next-generation Internet infrastructure. Assuming a network model in which a multiprotocol label switching (MPLS) layer is overlaid on top of a WDM layer, and a segregation of the traffic on a wavelength basis, the strategy is based on a network dimensioning aiming at: 1) the support of different types of traffic, relating to different service categories; 2) the guarantee that all the wavelength paths carrying mission-critical services (with stringent quality of service requirements) are protected against failure; and 3) the possibility of restoring a large amount of wavelength paths carrying Internet best-effort services, i.e., low-priority (LP) preemptible traffic with no QoS requirements. The reference network scenario is an overlay model in which the optical network interacts with an MPLS network with a separated control plane; the optical network manages its resources to better serve the traffic coming from the MPLS network. Two path protection schemes, namely, disjoint path (DP) and single-link basis (SLB), and a link protection mechanism, namely, local repair (LP), are investigated. Furthermore, the paper considers both the case of using wavelength conversion in the optical nodes and the case in which wavelength conversion is not used at all. The analysis compares the performance of the different strategies in terms of the percentage of optical paths carrying LP traffic not served by the optical network after a failure and of the dimensions of the optical nodes for all the schemes. The analysis reveals that the proposed approach allows the restoration of a large amount of best-effort traffic with a reasonable increase of network redundancy.