Showing papers on "Optical Transport Network published in 2009"

Spectrum-efficient and scalable elastic optical path network: architecture, benefits, and enabling technologies

Abstract: The sustained growth of data traffic volume calls for an introduction of an efficient and scalable transport platform for links of 100 Gb/s and beyond in the future optical network. In this article, after briefly reviewing the existing major technology options, we propose a novel, spectrum- efficient, and scalable optical transport network architecture called SLICE. The SLICE architecture enables sub-wavelength, superwavelength, and multiple-rate data traffic accommodation in a highly spectrum-efficient manner, thereby providing a fractional bandwidth service. Dynamic bandwidth variation of elastic optical paths provides network operators with new business opportunities offering cost-effective and highly available connectivity services through time-dependent bandwidth sharing, energy-efficient network operation, and highly survivable restoration with bandwidth squeezing. We also discuss an optical orthogonal frequency-division multiplexing-based flexible-rate transponder and a bandwidth-variable wavelength cross-connect as the enabling technologies of SLICE concept. Finally, we present the performance evaluation and technical challenges that arise in this new network architecture.

Physical layer impairment aware routing (PLIAR) in WDM optical networks: issues and challenges

Abstract: In WDM optical networks, the physical layer impairments (PLIs) and their significance depend on network type-opaque, translucent, or transparent; the reach-access, metro, or core/long-haul; the number and type of network elements-fiber, wavelengths, amplifiers, switching elements, etc.; and the type of applications-real-time, non-real time, missioncritical, etc. In transparent optical networks, PLIs incurred by non-ideal optical transmission media accumulate along an optical path, and the overall effect determines the feasibility of the lightpaths. If the received signal quality is not within the receiver sensitivity threshold, the receiver may not be able to correctly detect the optical signal and this may result in high bit-error rates. Hence, it is important to understand various PLIs and their effect on optical feasibility, analytical models, and monitoring and mitigation techniques. Introducing optical transparency in the physical layer on one hand leads to a dynamic, flexible optical layer with the possibility of adding intelligence such as optical performance monitoring, fault management, etc. On the other hand, transparency reduces the possibility of client layer interaction with the optical layer at intermediate nodes along the path. This has an impact on network design, planning, control, and management. Hence, it is important to understand the techniques that provide PLI information to the control plane protocols and that use this information efficiently to compute feasible routes and wavelengths. The purpose of this article is to provide a comprehensive survey of various PLIs, their effects, and the available modeling and mitigation techniques. We then present a comprehensive survey of various PLI-aware network design techniques, regenerator placement algorithms, routing and wavelength assignment algorithms, and PLI-aware failure recovery algorithms. Furthermore, we identify several important research issues that need to be addressed to realize dynamically reconfigurable next-generation optical networks. We also argue the need for PLI-aware control plane protocol extensions and present several interesting issues that need to be considered in order for these extensions to be deployed in real-world networks.

Dynamic optical mesh networks: Drivers, challenges and solutions for the future

Abstract: We discuss the scalability challenges facing the optical networks. Using the architecture based on spectrum-sliced elastic optical path network (SLICE), we demonstrate how the networking functionality can be effectively shifted to the optical domain.

Modulation and multiplexing in optical communication systems

Abstract: Digital electronics and optical transport The rapid transition from analog to digital systems over the past ~50 years has enabled universal processing of all kinds of information, fundamentally without loss of quality [1]. Breakthroughs in digital semiconductor technologies and their enormous ability to scale [2] have enabled cost-effective mass-production of richly functional yet highly reliable and power-efficient microchips that are found in virtually any electronic device today, from high-end internet routers to low-end consumer electronics. Closely coupled to the generation, processing, and storage of digital information is the need for data transport, ranging from short on-chip [3] and board-level [4,5] data buses all the way to long-haul transport networks spanning the globe [6,7] and to deep-space probes collecting scientific data [8], cf. Fig. 1 [5,10]. Each of these very different applications brings its own set of technical challenges, which can be addressed using electronic, radio-frequency (RF), or optical communication systems. Among the different communication technologies, optical communications generally has the edge over baseband electronic or RF transmission systems whenever high aggregate bit rates and/or long transmission distances are involved. Both advantages are deeply rooted in physics: First, the high optical carrier frequencies allow for high-capacity systems at small relative bandwidths. For example, a mere 2.5% bandwidth at a carrier frequency of 193 THz (1.55 μm wavelength) opens up a 5-THz chunk of continuous communication bandwidth. Such “narrow-band” systems are much easier to design than systems with a large relative bandwidth. Second, transmission losses at optical frequencies are usually very small compared to baseband electronic or RF technologies. Today’s optical telecommunication fibers exhibit losses of less than 0.2 dB/km; the loss of typical coaxial cables supporting ~1 GHz of bandwidth is 2 to 3 orders of magnitude higher. In free-space systems optical beams have much smaller divergence angles than in the microwave regime, at the expense of significantly exacerbated antenna pointing requirements, though. The narrow beam width favorably translates into the system’s link budget, in particular in space-based systems where atmospheric absorption is less of a problem. Apart from the above two major advantages, other considerations sometimes come into play, such as the unregulated spectrum in the optical regime or the absence of electromagnetic interference.

Concept and enabling technologies of spectrum-sliced elastic optical path network (SLICE)

Abstract: A novel, spectrum-efficient and scalable optical transport network architecture called spectrum-sliced “elastic optical path” network (SLICE) is presented. The SLICE architecture enables sub-wavelength, super-wavelength, multiple-rate data traffic accommodation, and elastic variation of allocated resources in a highly spectrum-efficient manner.

Optical OFDM: A promising high-speed optical transport technology

Abstract: Orthogonal frequency division multiplexing (OFDM) is a widely used modulation/multiplexing technology in wireless and data communications. Leveraging recent advances in high-speed complementary metal-oxide semiconductor (CMOS) technologies and optical modulation and detection technologies, optical OFDM at a 40Gb/s or even a 100Gb/s information rate becomes feasible. At the optical transmitter, OFDM is realized by a digital signal processor (DSP) using inverse fast Fourier transformation (iFFT) with subsequent digital-to-analog conversion and Cartesian electro-optic modulation. At the receiver, the signal optical field is first reconstructed, e.g., by coherent detection. Then reverse signal processing is applied to recover the original data. OFDM enables efficient compensation of transmission effects such as chromatic dispersion and polarization mode dispersion that often are prohibiting impairments to cost-effective realization of high-speed optical transport systems. In light of the emerging demand for a 100+ Gb/s data rate in future optical transport systems, optical OFDM is considered to be a promising enabling technology. In this paper, the optical OFDM architectures will be reviewed, and their performance under various system conditions will be discussed and compared with alternative technologies. The challenges in the implementation of optical OFDM will also be discussed.

Practical physical-layer encryption: The marriage of optical noise with traditional cryptography

Abstract: We describe an emerging method of encryption suitable for high-speed optical communication networks. This encryption protocol combines traditional electronic cryptographic algorithms with the physical effect of optical noise of quantum origin to create a highly secure method of secret communications. The resulting optical signal is compatible with today's high speed fiber optic infrastructure including optical amplification and add/drop multiplexing. Systems implementing this protocol can be constructed with common commercially available components. We describe experimental results obtained with a 2.5 Gb/s system. The encrypted signal is shown to travel error-free through >500 km of optical fiber. Simulations show that reaches and data rates consistent with modern long haul optical networks are attainable.

Optical technologies can improve the energy efficiency of networks

Abstract: Optical technologies, in comparison with electronic technologies, need less power to switch high bitrates and to interconnect farther subsystems. The paper discusses with specific examples how optics can improve the energy efficiency of networks and switches.

Optical fiber distributed wireless personal area network

Abstract: A Wireless Personal Area Network that provides multiple users with multi-gigabit-per-second data rate wireless connectivity and is integrated with an optical fiber distribution network is disclosed. Embodiments relate generally to an integrated fiber optic WPAN architecture that comprises multiple 57-66 GHz remotely located wireless access points interconnected with a centrally located distribution point using optical fiber links. The integrated network provides an efficient, flexible and scalable 57-66 GHz WPAN architecture since the fiber optic links accommodate the delivery of bandwidth intensive services to large numbers of users while seamlessly supporting the diversity of multi-gigabit-per-second data applications. Two approaches for the transport of the WPAN signals over the optical fiber signal distribution network are described. One technique for interconnecting the remote radio access points in the fiber distributed 57-66 GHz WPAN is via an optical fiber network which can transport the wireless signals over the fiber as ‘analog over fiber’. An alternative ‘digital over fiber’ signal transport scheme for the fiber distributed 57-66 GHz WPAN is also described which supports the transport of the multi-gigabit-per-second WPAN digital data streams over fiber.

Next-Generation Optical Access Networks

Abstract: First-generation optical access networks have now been well-defined. This talk will focus on second- and third- generation networks including graceful evolution from single-wavelength to WDM and increasing integration of optical and wireless technologies.

Over 100 Gb/s Electro-Optically Multiplexed OFDM for High-Capacity Optical Transport Network

Abstract: 100-Gb/s-class high-speed transmission technologies are essential to realize future 100 G Ethernet transmission over wide area networks. Optical OFDM (Orthogonal Frequency Division Multiplexing) is promising for high-speed transmission because of its narrow bandwidth and superior tolerance to chromatic dispersion and polarization mode dispersion. In this paper, we show numerically that the nonlinear tolerance of optical OFDM increases as the subcarriers is decreased and describe novel electro-optic subcarrier multiplexing scheme to generate an over 100 Gb/s high speed optical OFDM signal with a small number of subcarriers. We successfully generate a 100 G-class optical OFDM signal and demonstrate transmission over 80-km of ITU-T G.652 single-mode fiber without dispersion compensation.

High-Bit-Rate Dynamically Reconfigurable WDM–TDM Access Network

Abstract: The intensification of traffic in the access network requires the development of novel architectural solutions for a reconfigurable network topology and components based on optical technologies. We present a hybrid ring-shaped wavelength division multiplexing (WDM)-time division multiplexing (TDM) passive optical network (PON) that is capable of providing bandwidth on demand at high bit rates in a transparent and dynamic manner. Our cost-efficient and scalable network architecture is based on integratable components such as a wavelength-agile optical networking unit and a microring-resonator-based remote node. An appropriately modified control layer is introduced to manage the network. We also discuss the implementation of optical codes instead of time slots to take the step toward optical code division multiplexing (OCDM) WDM PONs that relieve the network of strict time scheduling of traffic and ranging. Therefore, an additional reduction of complexity in network management, improvement of network scalability, and a guarantee of fully symmetric traffic are foreseen for every user. Finally, we show a scenario for smooth migration from existing PON solutions to our WDM-TDM PON architecture.

Modulation and multiplexing in optical communications

Abstract: Starting with capacity- and sensitivity-constrained transport (fiber-optic networks, satellite links), optics is steadily replacing electronics, progressing into implementation-constrained (on-chip) applications. At the same time, significant innovations are needed to continue optical transport capacity scaling.

Energy efficiency and CAPEX minimization for backbone network planning: Is there a tradeoff?

Abstract: Energy efficiency and the minimization of capital expenditures (CAPEX) for network equipment are studied for two network architectures: IP over WDM and IP over OTN over WDM. Case study results from mixed integer linear programming (MILP) formulations indicate that a CAPEX optimized network yields solutions having minimum energy consumption for both architectures. However, it is shown that the most cost efficient architecture is not always the least energy consuming. We quantify the occurring tradeoff and observe that network equipment CAPEX are dominating in terms of cost. Additionally, it is observed that the relative power contribution of different network layers is independent of the average inter-node traffic demand for both studied architectures.

Methods and apparatus for performing directionless and contentionless wavelength addition and subtraction

Abstract: In today's reconfigurable optical add/drop multiplexer (ROADM) based optical node, ROADMs multiplex (and demultiplex) colored optical signals to form wavelength-division multiplexed (WDM) signals. Transponders connected to the ROADMs' add/drop ports convert noncolored optical signals to colored optical signals (and vice versa). Dedicating transponders to given ports degrades the node's ability to route around network failures. Example embodiments of the invention include an optical node and corresponding method for routing optical signals within an optical node that compensate for this inflexibility. The optical node may include two ROADMs to transmit respective WDM signals onto at least two internode network paths and a routing module that can direct channels of the same wavelength along different internode network paths. Advantageously, a transponder may transmit (receive) different signals at the same wavelength to (from) different network node interfaces within the optical node, thereby improving the optical node's ability to route around network failures.

Generation of optical millimeter-wave signals and vector formats using an integrated optical I/Q modulator [Invited]

Abstract: This study discusses two key technologies used in radio-over-fiber (RoF) systems, namely, the generation and transmission of millimeter-wave signals and optical modulation schemes capable of carrying vector signal formats and utilizing the continuous performance improvements offered by digital signal processing. A cost-effective frequency-quadrupling technique capable of generating millimeter-wave signals up to 72 GHz is proposed. The generated optical millimeter-wave signals have very high quality, with an optical carrier and harmonic distortion suppression ratio exceeding 36 dB. An optical modulation scheme that can support a 64-QAM, 16 Gbits/s orthogonal frequency-division multiplexing RoF system is also demonstrated. Results of this study demonstrate that both methods offer realistic solutions to support future wireless systems.

Systems and methods for rapid optical transport network circuit provisioning

Abstract: The present disclosure provides systems and methods for rapid circuit provisioning in Optical Transport Networks (OTN) using signaling and routing protocols thereby enabling fast mesh restoration. The present invention utilizes a shim layer between OTN messaging (e.g., GCC or High-Level Data Link Control (HDLC)) and the associated signaling and routing protocol (e.g., OSRP, GMPLS, etc.). If an ODUk Connection CTP or TTP needs to be created, the shim layer runs a fast “OTN Setup” protocol, while buffering out going OTN messages. Incoming messages are still processed and do not require additional buffering. The purpose of the OTN Setup protocol is to allow the OTUk to re-frame on its client ODUk, while buffering out-going messages. When re-framing completes, buffers are released and the OTN messaging resumes without dropping any of the signaling frames.

Photonics in switching: enabling technologies and subsystem design

Abstract: This paper describes recent research activities and results in the area of photonic switching carried out within the framework of the EU-funded e-Photon/ONe+ network of excellence, Virtual Department on Optical Switching. Technology aspects of photonics in switching and, in particular, recent advances in wavelength conversion, ring resonators, and packet switching and processing subsystems are presented as the building blocks for the implementation of a high-performance router for the next-generation Internet.

Method and apparatus for implementing non-blocking computer interconnection network using bidirectional optical switch

Abstract: According to an embodiment of the present disclosure, a bidirectional communications system includes a first non-blocking network including a bidirectional optical switch, a plurality of nodes, a plurality of optical transceivers connected between the bidirectional optical switch and the plurality of nodes, each optical transceiver including a transmitter, a receiver and an optical combiner, and a second network connected to at least one of the nodes and the at least one at least one bidirectional optical switch for control of a crossconnect.

Frame generating apparatus, optical transmission system, frame generating method, and optical transmission method

Abstract: A frame generating apparatus includes an optical-transport-network frame generator configured to generate an optical transport network frame from a client signal; and a frame decomposer configured to perform serial-parallel conversion on the optical transport network frame to generate a plurality of virtual lanes, where the optical-transport-network frame generator arranges frame synchronization bytes and virtual lane identifiers in an overhead area and/or a fixed stuff part so that a frame synchronization byte and a virtual lane identifier are arranged in each virtual lane.

Network coding in passive optical networks

Abstract: The application of network coding in passive optical networks is shown to provide benefits in intra-PON communication scenarios with respect to reducing the packet loss ratio and queuing delay in case of congestion.

Performance of translucent optical networks under dynamic traffic and uncertain physical-layer information

Abstract: This paper investigates the performance of translucent Optical Transport Networks (OTNs) under different traffic and knowledge conditions, varying from perfect knowledge to drifts and uncertainties in the physical-layer parameters. Our focus is on the regular operation of a translucent OTN, i.e., after the dimensioning and regenerator placement phase. Our contributions can be summarized as follows. Based on the computation of the Personicks Q factor, we introduce a new methodology for the assessment of the optical signal quality along a path, and show its application on a realistic example. We analyze the performance of both deterministic and predictive RWA techniques integrating this signal quality factor Q in the lightpath computation process. Our results confirm the effectiveness of predictive techniques to deal with the typical drifts and uncertainties in the physical-layer parameters, in contrast to the superior efficacy of deterministic approaches in case of perfect knowledge. Conversely to most previous works, where all wavelengths are assumed to have the same characteristics, we examine the case when the network is not perfectly compensated, so the Maximum Transmission Distance (MTD) of the different wavelength channels may vary. We show that blocking might increase dramatically when the MTD of the different wavelength channels is overlooked.

100km long reach upstream 36Gb/s-OFDMA-PON over a single wavelength with source-free ONUs

Abstract: We experimentally demonstrate 36-Gb/s source-free single-wavelength upstream OFDMA-PON transmission, enabled by ONU carrier suppression and coherent reception at the OLT. A BER ≪10−3 is reported over 100km SSMF and a 1:32 optical split.

Evaluation of Wavelength Requirements for Stratospheric Optical Transport Networks

Abstract: This paper addresses the concept of optical transport network based on high altitude platforms (HAPs) flying in lower stratosphere and equipped with optical communications payload. The stratospheric transport network is formed of optical links between HAPs and optical backhaul uplinks and downlinks between HAPs and ground stations (GSs) hosting gateways to the backbone network. In order to consider limitations of free space optics (FSO) for the dimensioning of stratospheric optical transport network (OTN), we investigate the physical layer aspects for a DWDM based optical interplatform link (IPL). Taking into account the physical constraints imposed by FSO, we estimate the number of wavelengths required for full interconnectivity without wavelength conversions. We are using an analytical approach for bus and full mesh regular topologies, and a numerical approach for circumcircled star, ring and star regular topologies. We also evaluate the performance of a representative network with irregular topology using different routing and wavelength assignment algorithms. We show that the number of wavelengths needed to achieve full interconnectivity strongly depends on the physical topology of the network, and that adaptive routing yields better overall performance of the network compared to fixed and fixed alternate routing. The analysis also shows that resources in realistic network topologies tend to be used very inefficiently, which could be improved by traffic engineering solutions or wavelength conversions.

Optical routing device and optical network using same

Abstract: The invention pertains to methods, apparatus, and systems optical of networking using tunable receivers, optical blocking elements selectively placed in the network, and optical routing elements comprised of passive elements, such as optical couplers and splitters. The routing elements have a plurality of ports and comprise passive elements such as couplers and splitters configured so that input light received at any port of the element is output from each of the other ports of the element, but not at port at which it was input.

Method, apparatus and system for transmitting and receiving client signals

Abstract: The present invention provides a method, apparatus and system for transmitting and receiving a client signal. The method for transmitting a client signal includes, at the transmitting end, mapping a client signal to be transmitted to a corresponding low-order Optical Channel Data Unit (ODU) in a low-order ODU set, wherein low-order ODUs in the low-order ODU set having rates increased in order, and having rate correspondence relations with the client signals; mapping the low-order ODU to a timeslot of a high-order Optical Channel Payload Unit (OPU) in a high-order OPU set; and adding overheads to the high-order OPU to form an Optical Channel Transport Unit (OTU), and transferring the OTU to an Optical Transport Network (OTN) for transmission.

Optical communications network node and method of controlling data transmission between optical communications network nodes

Abstract: An optical communications network node (10) comprising an optical transmitter module (16), an optical receiver module (12), an electrical cross-point switch (20) and control apparatus (24, 26). The optical transmitter module (16) comprises optical sources (18) each having a different operating wavelength and each being selectively assignable as an optical circuit switching channel source or an optical burst switching channel source. The optical receiver module (12) comprises a said plurality of optical detectors each operable at one of said operating wavelengths. The electrical cross-point switch (20) comprises switch paths (22) and is configurable to allocate a first set of switch paths for optical circuit switching and a second set of switch paths for optical burst switching. The control apparatus (24, 26) configures the switch paths (22), separates data traffic to be dropped from transit data traffic, and schedules data traffic for transmission on optical burst switching channels to the respective sources (18).

Physical layer security in fiber-optic networks using optical signal processing

Abstract: Using optical processing techniques, we experimentally enhance the physical layer security of optical communication systems. We exploit optical encryption using fiber nonlinearity to achieve real time data encryption. By implementing interleaved waveband switching modulation and variable two-code keying to the system, the security of the data is further enhanced. Based on spread spectrum, we also demonstrate optical steganography such that the stealth signal is transmitted underneath system noise. Optical steganography in WDM and optical CDMA systems is experimentally demonstrated. We also propose and study optical CDMA-based backup channels that improve service availability without wasting the bandwidth in the backup channel. The multi-layered security provided improves the confidentiality and availability of the network.

Design and Implementation of a GMPLS-Controlled Grooming-Capable Optical Transport Network

Abstract: Aiming at better resource utilization, an important requirement of future optical transport networks is the capability to accommodate subwavelength client flows efficiently. This can be put into action thanks to the enhanced traffic engineering (TE) protocols provided within the generalized multiprotocol label switching (GMPLS) standardization. The present paper concentrates on the design and implementation of a GMPLS-controlled grooming-capable transport infrastructure, namely, the automatically switched optical network (ASON)/GMPLS CARISMA test bed. Through the paper, the operation of a GMPLS-controlled multilayer network architecture is introduced, subsequently highlighting implementation issues that come to light. Special attention is devoted to a centralized flow reallocation module deployed in the CARISMA test bed to minimize the overall network cost. In this context, an integer linear programming (ILP) formulation to obtain its optimal cost is derived and low-weighted metaheuristics providing a nearly optimal solution are additionally proposed. All contributions in the paper are supported by illustrative experimental results.

Method and apparatus for mapping service integration onto optical channel delivery unit

Abstract: The present invention discloses a method for mapping service multiplexing to the optical channel transmission unit OTU. The method comprises the following steps: filling service data into the container block of at least one frame of OPU area container; and filling service clock information in the optical channel payload unit overhead OPU OH area, wherein the container block comprises at least one frame of OPU area container which is composed of at least one OPU area. The embodiment of the invention also provides a device for mapping service multiplexing to the optical channel transmission unit OUT. The technical plan of the invention can guarantee the high-performance transmission of clock information and simultaneously effectively reduces the complexity of transmitting and processing the service data as the service data and service clock information are transmitted separately. Furthermore the high-performance transmission of clock information can help to effectively filter the large number of shakes generated in OTN multiplexing mapping and de-mapping process of de-mapping receiving end, and recovers the high-performance clock.