Optical communications – Diagnostic testing – Determination of communication parameter
Reexamination Certificate
2000-12-22
2004-06-29
Pascal, Leslie (Department: 2633)
Optical communications
Diagnostic testing
Determination of communication parameter
C398S034000
Reexamination Certificate
active
06757494
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for routing wavelengths in a photonic network.
BACKGROUND OF THE INVENTION
In any optical or photonic network it may be expected that signal degradation occurs as signals are passed through nodes in the network. This is because in contrast to a conventional (non-optical) network, signals may be routed using entirely optical means and therefore do not necessarily undergo regeneration at each network node. Generally speaking, the degradation is correlated to the number of nodes which the signal has passed through. For example, in a photonic network a wavelength typically may be permitted to pass through a predetermined maximum number of amplifiers before the noise added at each amplifier becomes unacceptably high. Therefore in order to permit the use of long paths with many nodes, it is necessary to periodically regenerate the signal to maintain an adequate signal quality (specified for example in terms of an acceptable bit error rate [BER] or noise floor).
In the case of a wavelength division multiplexed (WDM) arrangement, regeneration typically takes the form of an optical-electrical-optical (OEO) conversion. Thus, in routing a path through a photonic network carrying such multiplexed wavelengths, it is necessary to provision regenerative nodes at suitable intervals along the path. However, it will be noted that a node (such as an optical cross connect [OXC]) carries an additional cost over that of a simpler, optically transparent photonic cross connect (PXC) or an amplifier. Thus It is desirable to minimise the use of regenerative nodes in any cone path in order to reduce overall network costs.
Thus in principle, it is desirable to cause each path through the network to traverse as many amplifiers as possible before being regenerated (in order to reduce the number of regenerative nodes required) but to ensure that no path is allowed to traverse mote than a predetermined maximum number of amplifiers (that number being selected to ensure that the signal is not excessively degraded before regeneration).
In practice, selecting such paths particularly in a mesh network with many routing choices, is very complex.
Algorithms have been developed which are suitable for use in a centralised planning arrangement where network configuration is controlled centrally and is only periodically altered. However, it is desirable to provide an agile dynamic deployment of wavelengths across a photonic network and prior art algorithms are too cumbersome for such uses.
SUMMARY OF THE INVENTION
In accordance with a first aspect, the invention may provide a network configuration tool for a photonic network comprising a route generator operable to generate a list of possible paths through the network between a first and second node in the network, an non-regenerative node counter operable to determine for each of the possible paths whether the respective path traverses a number of non-regenerative nodes which is greater than a predetermined maximum number of non-regenerative nodes, a non-regenerative path selector operable to select a path from the set of paths which have been determined not to traverse a number of non-regenerative nodes which is greater than the said maximum number of non-regenerative nodes, and to output the selected path, a path rejecter operable to reject any paths which are determined to traverse a number of non-regenerative nodes which is greater than the said maximum non-regenerative node value and which do not traverse regenerative nodes, a Path shortener operable to generate for each possible path, a set of shortened paths, each shortened path passing between the said first node and a regenerative node in the respective possible path, the non-regenerative node counter being further operable to determine for each shortened path whether the shortened path traverses a number of non-regenerative nodes which is greater than the predetermined maximum number of non-regenerative nodes, and a regenerative path selector operable to select a regenerated path by choosing a possible path which corresponds to a shortened path determined not to traverse a number of non-regenerative nodes which is greater than the predetermined maximum number of non-regenerative nodes, the regenerated path being provisioned to include a regeneration at the node corresponding to the end node of the shortened path, and the regenerative path selector being further operable to output the selected regenerative path.
The invention may in a second aspect, provide a network manager for a photonic network comprising an non-regenerative node counter operable to determine for each of a plurality of possible paths through the network between a first and second node in the network, whether the respective path traverses a number of non-regenerative nodes which is greater than a predetermined maximum number of non-regenerative nodes, a non-regenerative path selector operable to select a path from set of paths which have been determined not to traverse a number of non-regenerative nodes which is greater than the said maximum number of non-regenerative nodes, and to output the selected path, a path rejecter operable to reject any paths which are determined to traverse a number of non-regenerative nodes which is greater than the said maximum non-regenerative node value and which do not traverse regenerative nodes, a path shortener operable to generate for each possible path, a set of shortened paths, each shortened path passing between the said first node and a regenerative node in the respective possible path, the non-regenerative node counter being further operable to determine for each shortened path whether the shortened path traverses a number of non-regenerative nodes which is greater than the predetermined maximum number of non-regenerative nodes, and a regenerative path selector operable to select a regenerated path by choosing a possible path which corresponds to a shortened path determined not to traverse a number of non-regenerative nodes which is greater than the predetermined maximum number of non-regenerative nodes, the regenerated path being provisioned to include a regeneration at the node corresponding to the end node of the respective shortened path, and the regenerative path selector being further operable to output the selected regenerative path.
In another aspect, the invention provides a method of selecting a route through a photonic network comprising selecting nodes in the route based on the signal degradation between optical regenerators in the route. The signal degradation may be measured by counting non-regenerative nodes. Alternatively or additionally, measurements of the signal may be made such as BER or noise, and the measurement may be compared with a threshold beyond which provisioning of regeneration in the route is considered necessary. The measurements may be made, for example, using the techniques disclosed in Nortel Networks co-pending U.S. patent application “Optical Networks with Signal Regeneration”, (Nortel reference 12947D) which was filed on Dec. 6, 2000.
In a further aspect of the invention there is provided a method of selecting a wavelength route between a first and a second node in a photonic network comprising the steps of determining for each of a plurality of possible paths between the first and second nodes, whether the respective path traverses a number of non-regenerative nodes which is greater than a predetermined maximum number of non-regenerative nodes, for the set of possible paths determined not to traverse a number of non-regenerative nodes which is greater than the said maximum number of non-regenerative nodes, selecting a non-regenerated path from the set, if all possible paths are determined to traverse a number of non-regenerative nodes which is greater than the said maximum non-regenerative node value, rejecting any paths which do not traverse regenerative nodes, generating for each possible path, a set of shortened paths, each shortened path passing between the said first
Briggs Alan R
Lu Xiang
Warbrick Kevin
Barnes & Thornburg LLP
Bello Agustin
Nortel Networks Limited
Pascal Leslie
LandOfFree
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