Nortel Networks Corporation

Peter Jeremy Anslow

Richard W Heath

Richard E Epworth

Alan Glen Solheim

Peter David Roorda

Matthew D Brown

Richard A Habel

Adrian Paul Sparks

Christopher R Fludger

Peter T H Kwa

A method of transmitting packet traffic between first and second network nodes in a shared protection optical transmission network, the method comprising defining first and second traffic paths between said nodes, at least one of said paths being a shared protection path, and allocating traffic along said paths utilising link aggregation.

Load sharing nodes in a network utilising shared optical protection

The distortion component of an optical signal received from an optical transmission system, such as an all-optical system, subject to noise and amplitude distortion components, can be evaluated by a method that utilises information derived from analysing the bit error ratio (BER) of the signal as a function of a movable threshold. The analysis is performed in high and low bit error ratio areas of the eye diagram used for data one/zero decision making. The intersections with the threshold axis (where BER=0.25) of extrapolations of the high and low bit error ratio values provide variables Vand Vwhich are divided (V/V) to obtain an estimate/prediction of the amplitude closure of the eye diagram resulting from amplitude distortion. The analysis is preferably carried out after Q conversion of the BER values. The method can also be extended to provide indications of Q, bit error ratio and optical signal-to-noise ratio within the signal.

Distortion measurement in optical communication systems

Use in an optical communications system of multiple detectors to separately detect respective multiple spectral modes of a received optical signal. The invention also provides for corresponding multi-channel, dispersion-tolerant optical receivers. Embodiments are presented both for direct detection and for coherent detection of optical signals.

Multi-detector detection of optical signals

A client signal received at an ingress interface is adapted to a higher-rate transport signal. Clock frequency acceleration is achieved by an M/N-multiplying PLL where the magnitude of M and N can be restricted without causing the rate of the resulting transport signal rate to deviate unacceptably from a nominal transport signal rate. Each frame of the transport signal has a payload section with a fixed number of transport payload bytes, each of which is either a dummy byte or a client byte. The number of client bytes per transport frame is within one byte of the number of client bytes actually received at the ingress interface during the duration of the frame. The designation of each frame as a low-fill frame or a high-fill frame is automatically regulated by checking the fill level of a memory element and is redundantly encoded by the ingress interface and transmitted to an egress interface as part of the frame.

Processing of arbitrarily formatted client signals to achieve compatibility with existing transport networks

An apparatus for determining an error ratio of individual channels of a WDM optical signal comprises a wavelength-selective filter for separating the individual channels of the WDM signal and a measurement circuit for measuring an error ratio of one channel using a first decision threshold level. The measurement circuit is operable to cycle through all channels, taking an error ratio measurement for each channel in sequence with a predetermined decision threshold level. Control circuitry alters the decision threshold level for successive cycles of the measurement circuit. The apparatus measures error ratio values for each channel in turn, building up an error ratio vs. threshold pattern enabling the Q value to be obtained. Although the time taken to build up the error ratio pattern for an individual channel is not shortened, measurements are taken on each channel at much shorter intervals. This means that signal degradations can be detected much more rapidly, as these signal degradations will be reflected in each error ratio measurements, and do not require a completely updated error ratio pattern to be obtained.

Method and apparatus for rapidly measuring optical transmission characteristics in photonic networks

A WDM optical network comprising a plurality of nodes has a first apparatus for optical analysis at the site of a first optical amplifier upstream of the first node, a second apparatus for optical analysis at the site of a second optical amplifier at the downstream output of the first node, and a third apparatus for optical analysis at the site of a third optical amplifier further downstream of the first node, where knowledge of the optical sin to noise ratio (OSNR) is desired. The first, second and third apparatus are for measuring the signal level at frequencies both at and in-between the channel frequencies. The signal levels at the channel frequencies and between the channel frequencies at the first, second and third apparatus are used to derive the OSNR at the third apparatus. This enables the OSNR to be measured accurately at any site in the network, using calculations in which noise shaping of the nodes can be factored in to the calculation of OSNR.

Method and apparatus for measuring and estimating optical signal to noise ratio in photonic networks

The method of monitoring the quality of an optical signal at the site of a R or R regenerator, without performing a clock recovery operation, is based on slicing the recovered voltage with a threshold voltage, manipulated according to a pattern, and averaging the output of the slicer. An eye diagram is simulated by a diagram representing the average voltage versus the threshold voltage.

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Bishops Stortford, United Kingdom

Peter Jeremy Anslow