Abstract:
A method and system for network wide fault isolation in an optical network are described. A single fault in a network can produce a large number of alarms at different points in an optical network. The described method and system identify the root cause alarm while masking all correlated alarms. In the embodiment of the invention, the method and system are based on a wavelength tracker technology allowing identification and tracking of individual channels in the optical network.
Abstract:
Cascaded policing methods and systems are provided which allow lower priority traffic to benefit from otherwise unused capacity allocated to higher priority traffic of a given customer/service with multiple classes of service. The method involves policing packets of a first class in accordance with at least one policing parameter associated with the first class, and policing packets of a second class in accordance with at least one policing parameter associated with the second class in a manner which gives to the second class at least a portion of a traffic throughput afforded to the first class by at least one of said at least one policing parameter, such as a rate guarantee or burst tolerance, associated with the first class of traffic which is not being used by the packets of the first class. The method is easily adapted to an arbitrary number of different traffic classes.
Abstract:
Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.
Abstract:
Optical communication networks often incorporate fiber rings or fiber mesh topologies for interconnecting its nodes. Both of these topologies can contain closed optical loops at one or more wavelengths within the optical spectrum. In amplified optical systems, the inherent loss of these optical loops is counteracted by the amplifier gain. Thus, the optical loop may have a net loss that is too low to prevent excessive noise buildup resulting in a lasing fiber loop. The noise that builds up within such amplified systems is dominated by the Amplified Spontaneous Emission (ASE) noise resulting in ASE loops. Such loops can have a serious impact on all wavelengths carried by the fiber and lead to a partial or complete loss of end to end communication due to a severe degradation in signal to noise ratio. This invention provides an effective method and system for avoiding ASE loops in optical communication networks. The method deploys optical seams as well as a unique signature for a wavelength instance for achieving an effective solution that is resilient to errors and failures that may occur on the system both during service creation and normal operation.
Abstract:
Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.
Abstract:
The invention provides a method which involves inserting probe packets on a per service basis for transmission on a respective round trip; and for each service using the probe packets to calculate packet latency for probe packets which is representative of packet latency for all packets transmitted for the service. In some embodiments, data plane time stamps are used to accurately time probe latency. The invention also provides a method which involves inserting probe packets on a per service basis for transmission on a respective destination network element; and at the destination network element for a given service using the probe packets to calculate one way packet loss for the service.
Abstract:
A method and system for allocating and controlling a hierarchy of labels in an MPLS network is provided. The hierarchy of labels, inserted into MPLS packets, is introduced so as to correspond to the hierarchy of sub-flows within a data flow. The labels have the established dependency so that positions of labels in the hierarchy identify a sequence of processing the labels and functions associated with the labels. The system for allocating and controlling the hierarchy of MPLS labels includes a first control plane mapper for releasing available labels, a first controller for assigning the released labels according to the hierarchy, means for transmitting the labels in the network, a second controller for detecting the labels, and a second control plane mapper for maintaining current label dependency within the hierarchy. If required, re-addressing of the hierarchy of labels may be performed to maintain flow-sub-flow association throughout two adjacent networks. In the preferred embodiments on the invention the method of allocating and controlling hierarchy of labels is applied to sub-flows within FA-LSP flows, and to multi-cast services in the network associated with a function of flooding and filtering data within a network node.
Abstract:
Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.
Abstract:
This invention describes a method for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, comprising the steps of measuring power of the optical signal at the VOA; comparing the measured power with a target power; and if the measured power differs from the target power, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power, wherein the VSI being a function of the measured power and target power. The method further comprises the step of comparing the measured power with a Loss-of-signal (LOS) power threshold, and if the measured power is less than the LOS power threshold, changing the attenuation of the VOA in one or more variable size intervals so that the power of the optical signal substantially higher than the LOS power threshold, wherein the size of the variable interval being a function of the measured power and the LOS power threshold. The method dynamically computes a VSI, updates the VOA setting by said VSI, and manages a combination of open and closed VOA control loops to maintain the target power attenuation of the VOA The corresponding apparatus for controlling the VOA is also provided.
Abstract:
A method and apparatus for performing a fast Fourier transform (FFT) computation on large data sizes in real time is provided. The speed at which a FFT is performed is increased by reducing the number of times a Direct Memory Access (DMA) unit must transfer data between an internal memory and an external memory. This is achieved through an algorithm in which data is imported from the external memory into the internal memory and having the CPU perform several calculations on the imported data before it is exported back to the external memory. The imported data in the internal memory has a structure that results in a reduction of the number of times the imported data is swapped between different layers of the internal memory during the FFT computation. Furthermore, the DMA unit import/exports data between the internal memory and the external memory while at the same time having the CPU perform calculations on other data in the internal memory.