Showing papers on "Optical Transport Network published in 2001"

Issues for routing in the optical layer

Abstract: Optical layer control planes based on MPLS and other Internet protocols hold great promise because of their proven scalability, ability to support rapid provisioning, and auto discovery and self-inventory capabilities and are under intense study in various standards bodies. To date however little attention has been paid to aspects of the optical layer which differ from those found in data networking. We study three such aspects which impact routing: network elements which are reconfigurable, but in constrained ways; transmission impairments which may make some routes unusable; and diversity. We conclude that if emerging optical technology is to be maximally exploited, heterogeneous technologies with dissimilar routing constraints are likely. Four alternative architectures for dealing with this eventuality are identified and some trade-offs between centralizing or distributing some aspects of routing are discussed.

The application of optical packet switching in future communication networks

Abstract: Telecommunication networks are experiencing a dramatic increase in demand for capacity, much of it related to the exponential takeup of the Internet and associated services. To support this demand economically, transport networks are evolving to provide a reconfigurable optical layer which, with optical cross-connects, will realize a high-bandwidth flexible core. As well as providing large capacity, this new layer will be required to support new services such as rapid provisioning of an end-to-end connection under customer control. The first phase of network evolution, therefore, will provide a circuit-switched optical layer characterized by high capacity and fast circuit provisioning. In the longer term, it is currently envisaged that the bandwidth efficiency associated with optical packet switching (a transport technology that matches the bursty nature of multimedia traffic) will be required to ensure economic use of network resources. This article considers possible network application scenarios for optical packet switching. In particular, it focuses on the concept of an optical packet router as an edge network device, functioning as an interface between the electronic and optical domains. In this application it can provide a scalable and efficient IP traffic aggregator that may provide greater flexibility and efficiency than an electronic terabit router with reduced cost. The discussion considers the main technical issues relating to the concept and its implementation.

Ethernet PON (ePON): Design and Analysis of an Optical Access Network

Abstract: With the expansion of services offered over the Internet, the “last mile” bottleneck problems continue to exacerbate. A passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we propose the design and analysis of a PON architecture which has an excellent performance-to-cost ratio. This architecture uses the time-division multiplexing (TDM) approach to deliver data encapsulated in Ethernet packets from a collection of optical network units (ONUs) to a central optical line terminal (OLT) over the PON access network. The OLT, in turn, is connected to the rest of the Internet. A simulation model is used to analyze the system’s performance such as bounds on packets delay and queue occupancy. Then, we discuss the possibility of improving the bandwidth utilization by means of timeslot size adjustment, and by packet scheduling.

Multiprotocol lambda switching: combining MPLS traffic engineering control with optical crossconnects

Abstract: This article describes an approach to the design of control planes for optical crossconnects which leverages existing control plane techniques developed for MPLS traffic engineering. The proposed approach combines recent advances in MPLS traffic engineering control plane constructs with OXC technology to provide a framework for real-time provisioning of optical channels, foster development and deployment of a new class of OXCs, and allow the use of uniform semantics for network management and operations control in hybrid networks consisting of OXCs and label switching routers. The proposed approach is particularly advantageous for OXCs intended for data-centric optical internetworking systems.

Progress in optical networking

Abstract: This article summarizes the present state of optical networking, how we got to this point, and what needs to be done to complete the job. The point of departure is an assumed future two-level structure in which the transport is by means of steadily growing interconnected all-optical islands of transparency, while the remainder of the communication layers are based on IP, both levels being managed by an MPLS-based control plane. After reviewing why such networks are becoming inevitable, a review is given of the various optical layer technology and architecture bottlenecks that have had to be solved. Issues that remain center on increasing the number of channels and reducing the technology costs.

Challenges for MPLS in optical network restoration

Abstract: Previous standards proposals have focused on extending IP-based MPLS protocols to optical networks. These proposals have concentrated on provisioning optical connections. However, a key expectation of the optical network is that it will offer fast restoration capability, competitive in performance to SONET rings. To meet this expectation, there are key features that need to be added to the current proposals to extend MPLS for the optical network. This article discusses some of these key requirements.

The perspective of optical packet switching in IP dominant backbone and metropolitan networks

Abstract: 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.

Design of photonic rearrangeable networks with zero first-order switching-element-crosstalk

Abstract: The development of optical cross-connect architectures is a very important topic today. We consider here in particular the class of optical space-division switching fabrics configured as multistage structures built with 2/spl times/2 optical switching elements (SEs) and derived from a combination of vertical replication and horizontal expansion of Banyan networks. We determine the necessary and sufficient conditions for these matrices to be rearrangeably nonblocking and free of first-order crosstalk in SEs. This impairment is one of the major limitations in optical cross-connect performance. We focus on rearrangeable matrices since they have lower complexity than their strict-sense nonblocking counterparts. Given the current high cost of optical SEs, the rearrangeable solution looks attractive today.

Passive optical network employing coarse wavelength division multiplexing and related methods

Abstract: A passive optical network in which a plurality of wavelength division multiplexed optical signals are exchanged between terminals. At an upstream node such, for example, as a central office, a first plurality of coarsely wavelength division (CWDM) multiplexed optical signals are launched onto or otherwise supplied to a first optical fiber, which fiber may carry optical signals in one or both of the upstream and downstream directions. The downstream or first plurality of coarsely wavelength division multiplexed optical signals, carried via the first optical fiber, are supplied to and distributed by a passive optical node to respective optical network terminals. Each optical network terminal is associated, for example, with a corresponding multiple tenant unit (MTU) such as a commercial office building, a multiple dwelling unit (MDU) such as an apartment, or a fiber to the home (FTTH) grouping of subscribers, and receives at least one of the optical signals from the passive optical node and transmits at least one optical signal to the passive optical node. At the passive node, the optical signals received from the respective optical network terminals are coarsely wavelength division multiplexed again for transmission to the upstream node. The nominal spacing between WDM wavelengths carried over each fiber of the PON is sufficiently great as to obviate temperature stabilized lasers which would otherwise be required at the optical network terminals to avoid cross-talk between adjacent CWDM optical signals.

Architectures and protocols that enable new applications on optical networks

Abstract: This article first discusses how advances in networking architectures and protocols can complement advances in optical communications research to increase the overall value of optical networks by enabling more applications. A review of existing optical networking solutions is then provided along with a classification of different types of optical networks. Finally, we show how single-hop and multihop wavelength-routed networks can be used efficiently for fast end-to-end file transfers when these networks are equipped with a hardware-implementable signaling protocol, a routing protocol, and a simple transport protocol.

WDM optical communication system with channels supporting multiple data formats

Abstract: The present invention provides a flexible WDM optical communication system in which each optical channel of the WDM optical communication signal can simultaneously accept multiple data formats. In one embodiment, the WDM optical system includes an optical waveguide having an optical add-drop multiplexer to selectively add and/or drop one or more optical channels to/from the WDM signal carried on the waveguide. A first source of data imparts information onto a first optical channel in a packet format while a second source of data imparts information onto the first optical channel in a time division multiplexed format. Other data sources having other data formats may also be included. An optical network interface electrically communicates with the data sources, placing the data from these sources onto the first optical channel which is generated from an optical source such as a laser. An optical path carries the optical channel from the optical source to the optical add-drop multiplexer. From there, it is multiplexed onto the optical waveguide, merging with the other optical channels of the WDM optical signal.

Optical transport networks

Abstract: The present invention provides an optical packet switch (3, 4) that facilitates efficient provisioning of packet services through a predominantly circuit-switched optical transport network infrastructure (1). In particular, the optical packet switch (3, 4) fits within a network where circuit and packet-switched traffic are transported together through the optical transport network (1). Fast switching is provided for packet traffic where granularity below the wavelength level is required, while slow wavelength switching and routing is facilitated at the same time. Fast switching and packet traffic aggregation for efficient bandwidth utilisation is performed at the edge where the optical transport network (1) interfaces with the IP domain (6), where dynamic and fast wavelength allocation for packet traffic is required.

First demonstration of an asynchronous optical packet switching matrix prototype for multi-terabit-class routers/switches

Abstract: An optical packet switching matrix for multi-terabit-class routers/switches has been prototyped. It is based on novel integrated optical gate arrays and asynchronous packet-mode receivers. Full asynchronous operation with 10 Gbit/s RZ optical packets is demonstrated for the first time.

RINGO: a WDM ring optical packet network demonstrator

Abstract: The RINGO network is based on a WDM optical ring, with input queueing access protocol and multicast capabilities. We present the network architecture, node structure and the results obtained on the experimental testbed.

Method and system for compensating for chromatic dispersion in an optical network

Abstract: The present invention provides a method and system for compensating for chromatic dispersion in an optical network. The method and system includes analyzing an optical signal at a first location in the optical network and determining if an eye of the optical signal has a desired shape at the first location. The method and system further includes automatically adjusting a dispersion of the optical signal at a second or at any location in the optical network if the optical signal does not have the desired shape; providing feedback concerning the shape of the adjusted optical signal at the first location; and automatically readjusting the dispersion of the optical signal at the second location based upon the feedback until the optical signal has the desired shape at the first location. The method and system of the present invention automatically compensates for dispersion in an optical system. This saves the network operator considerable time and raises the reliability. The method and system could be used to provide a continuous range of dispersion compensation to particular locations in the network or to the network as a whole, and to store information in a database to be used to produce dispersion maps for the network. It also provides the ability to dial in dispersion for changing fiber characteristics and pre-tuning in a switching of wavelengths from one system to another. Finally, it avoids extraordinary expense by allowing the approximation of the installed fiber dispersion without requiring field measurements.

Systems and methods for path set-up in a quantum key distribution network

Abstract: A system establishes a path for distributing data through an optical network ( 115 ). The system includes an optical switch ( 205 a ) and a data distribution endpoint ( 105 a ). The optical switch ( 205 a ) establishes a first encryption key distribution path through the optical network ( 115 ), the first encryption key distribution path including multiple optical switches and optical links. The data distribution endpoint ( 105 a ) determines whether eavesdropping has occurred on the first encryption key distribution path using quantum cryptography. The optical switch ( 205 a ) further establishes a second data distribution path through the optical network ( 115 ) responsive to the eavesdropping determination. The second encryption key distribution path includes multiple optical switches and optical links.

On an IP-centric optical control plane

Abstract: This article presents an experimental study on adopting and integrating the existing IP protocols and mechanisms into an optical network control plane. Although there has been much research effort on the conceptual and functional requirements for the control of optical networks, this article focuses on the design and implementation of an optical control plane. The proposed control plane implements the key functions such as routing, signaling, protection/restoration, and quality of service.

Network transceiver for extending the bandwidth of optical fiber-based network infrastructure

Abstract: A multimode wavelength division multiplexing (WDM) network transceiver and method includes a plurality of optical transmitters and a multiplexer operatively connected to each optical transmitter for receiving optical communications signals and multiplexing the signals into a multimode wavelength division multiplexed optical communications signal. A demultiplexer receives a multimode wavelength division multiplexed optical communications signal and demultiplexes the signal into a plurality of demultiplexed optical communications signals that are then received and detected within a plurality of optical receivers.

Optical transmission system constructing method and system

Abstract: An optical transmission system accomplishes optical transmission to a long distance by combining a multiplexing line terminal with optical amplifiers, linear repeaters, and regenerators with optical amplifiers combined together. The system also accomplishes the optical transmission to a short distance by directly connecting the linear terminals therebetween, with an electric-to-optic converter replaced by an electric-to-optic converter having a semiconductor amplifier, with an optic-to-electric converter by an optic-to-electric converter having an avalanche photodiode as light receiver, an with no use of any optical booster amplifier and optical preamplifier in the multiplexing line terminal. With these, the optical transmission system can be easily constructed depending on the transmission distance required.

Optical network system with quality control function

Abstract: To ensure transmission in a flexible optical network system, a digital test signal generation/comparison circuit is incorporated in an electrical signal processing portion of a transponder. The optical network system provides transparent wavelength-division multiplex service regardless of the signal type in client optical signals. Prior to connecting a client optical line to the optical system, a selective insertion unit and a selective extraction unit enable quality assessment of the client optical line.

Self aligning optical interconnect with multiple opto-electronic devices per fiber channel

Abstract: A method for alignment in software and supporting circuitry of the optical transmitters and receivers to their respective optical channels at each connection of a multi-channel optical link to an optical planar array, permits non-critical physical alignment of the connector to the optical array. The steps include: employing a connector and optical array configuration at each connection in which there are several optical devices within the illumination area of each channel at the connector/array interface, employing supporting circuitry and software that has control of all optical devices associated with the optical link, enabling all receivers, turning on the transmitters sequentially, recording which of the receivers is responding, comparing matching receiver sets for each transmitter to identify associated transmitter sets and channels.

Optical network with dynamic balancing

Abstract: An optical fiber network comprises a plurality of communications nodes. Each node is able to communicate utilizing multiplexed optical signals comprising a plurality of optical wavelength components. A plurality of optical fiber links interconnects the nodes. A dynamic balancer is inserted into each corresponding optical fiber links. Each dynamic balancer adjusts the intensities of a plurality of optical wavelength components in multiplexed optical signals transmitted over the optical fiber link.

Wavelength routing based on physical impairments

Abstract: A set of guidelines for routing wavelengths in switched optical networks that is based on physical constraints is presented. Impact on signaling protocols is also discussed. One may still choose to break down the automatically switched optical network (ASON) into multiple sub-networks, but the choice will now be based on administrative or business considerations rather than physical constraints. Hence, we shall concentrate on the methods that may be employed in estimating the quality of service for a transparent wavelength connection through such an ASON.

Establishment and maintenance of optical links between optical transceiver nodes in free-space optical communications networks

Abstract: A system and method for establishing and maintaining optical links between optical transceiver nodes in a free space optical communications network is disclosed. The system and method provide a protocol for acquisition of an optical link between transceivers in two adjacent nodes and for re-acquisition should a node be replaced or moved. The system and method also provide a protocol for tracking small movements of one or both nodes in a link. Also, the system and method provide a protocol for recovering a link that is temporarily lost.

SLSP: a new path protection scheme for the optical Internet

Abstract: The Short Leap Shared Protection (SLSP) is a new scheme for end-to-end path protection for the optical Internet. The paper presents the design and operation of SLSP in MPLS-based optical networks.

Interferometric ultrafast SOA-based optical switches: From devices to applications

Abstract: All-optical switches are fundamental building blocks for future, high-speed optical networks that utilize optical time division multiplexing (OTDM) techniques to achieve single channel data rates exceeding 100 Gb/s. Interferometric optical switches using semiconductor optical amplifier (SOA) non-linearities perform efficient optical switching with < 500 fJ of control energy and are approaching optical sampling bandwidths of nearly 1 THz. In this paper, we review work underway at Princeton University to characterize and demonstrate these optical switches as processing elements in practical networks and systems. Three interferometric optical switch geometries are presented and characterized. We discuss limitations on the minimum temporal width of the switching window and prospects for integrating the devices. Using these optical switches as demultiplexers, we demonstrate two 100-Gb/s testbeds for photonic packet switching. In addition to the optical networking applications, we have explored simultaneous wavelength conversion and pulse width management. We have also designed high bandwidth sampling systems using SOA-based optical switches as analog optical sampling gates capable of analyzing optical waveforms with bandwidths exceeding 100 GHz. We believe these devices represent a versatile approach to all-optical processing as a variety of applications can be performed without significantly changing the device architecture.

Wavelength allocation algorithms in optical buffers

Abstract: This paper addresses the problem of buffering performance optimization for asynchronous, variable length packets in a DWDM optical network. In the case of a multiplexing scheme that shares the wavelength resource among all packets regardless the connection they belong to, the problem of defining a wavelength allocation algorithm arises. Wavelength allocation has to be merged with delay allocation in buffers realized by means of fiber delay lines (FDLs). This paper proposes several allocation algorithms and compares their performance. It shows that the buffering performance strongly depends on the choice of the delay unit of the FDL's and that the algorithm aiming at reducing the artificial increase in the load due to the discrete time scale of the buffer gives best performance.

Comparison of centralized and distributed provisioning of lightpaths in optical networks

Abstract: This paper compares centralized and distributed online provisioning approaches in optical networks. In the centralized approach, complete network state is available for path computation. In the distributed approach, summarized information is available for path computation.

Node apparatus, optical wavelength division multiplexing network, and system switching method

Abstract: An optical wavelength division multiplexing network has a multi-level structure where a plurality of optical network units (ONUs) are connected to a lowest-level network. A node apparatus connected to networks other than the lowest-level network includes (a) passive optical components to branch optical signals from a higher-level network to a lower-level network, and couple optical signals from the lower-level network to the higher-level network, and (b) optical amplifiers for the optical signals. A node apparatus connected to the lowest-level network includes (a) an optical multiplexer/de-multiplexer to de-multiplex optical signals from the higher-level network, selectively output an optical signal to each ONU, and multiplex wave-length specific optical signals from the ONUs into a multiplexed optical signal, and (b) optical amplifiers for the optical signals. The node apparatuses provide an optical communication path between the higher-level network and the lower-level (or lowest-level) network without converting the optical signals into electrical signals.

Optical network terminator

Abstract: An optical network terminator for terminating and reducing the accumulated noise in optical networks, particularly ring based networks. The terminator eliminates problems of noise accumulation from amplifier spontaneous emission (ASE), thermal noise, etc., while providing bi-directional communications in the optical network. The optical network may have any topology including ring, star, mesh, point-to-point, etc. In the case of an optical ring, the ring is broken and an optical terminator is placed in line therewith. The optical network terminator includes a filer such as an optical demultiplexer/multiplexer or Fiber Bragg Grating (FBG) based filter. Each individual wavelength of light is filtered and a multi-wavelength optical output is generated whereby the noise accumulation is removed. Each channel is adapted to only pass a band-limited signal around the center frequency corresponding to the wavelengths supported by the particular optical ring network. Channel equalization uses variable optical attenuators and monitors in line with each channel. Channels currently not in use may be disconnected from the ring remotely by setting the corresponding optical attenuator to a low enough level.