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A Presentation on

Design and Implementation of Wavelength-Flexible Network

Nodes

Carl Nuzman, Juerg Leuthold, Roland Ryf, S.Chandrasekar, c. Randy Giles and David T. Neilson

By

Sudharshan Reddy .B

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Contents

• What is this presentation about ?

• Node Architectures

• Wavelength flexibility in the networks

• Analytic Estimate of Converter Placement

• A brief discussion on Implementation details

• Conclusion

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What is this presentation about?

• Analytically and Experimentally examination of node architectures for wavelength routing networks

• Wavelength flexibility simplifies network management and increases network capacity

• In a sharable pool, with fixed number of wavelength channels per fiber, the number of WC’s required remains low as the overall capacity is scaled up.

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What is this presentation about?

• Wavelength- routing networks provide a flexible optical network layer where light paths can be dynamically provisioned.

• To what extent wavelength conversion be available at the network nodes, and how might wavelength conversion be implemented.

• More insight into the size of the optical cross connects (OXC’s) needed to implement nodes of different designs in a given network.

• Discussion on cross-connect and wavelength conversion technologies that could be used at wavelength flexible network nodes.

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Node Architectures• Most existing wavelength routing networks use digital

cross-connect switches.

• A node is made opaque in the sense that the optical signals on every link are insulated and isolated from the signals on other links by electronic equipment.

• Converters can be classified as fixed or tunable output wavelength respectively.

• Wavelength converters can be classified according to the level of generation they provide i.e. WCs based on optical-electronic translation typically provide 3R regeneration (re-amplification, reshaping, retiming), while typical all optical converters provide 2R regeneration (reamplification and regeneration)

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Node Architectures

• There are many tradeoffs between different designs of the nodes.

• The simplicity of the node designs results in number of networking challenges like increased complexity of routing and wavelength assignment , increased sophistication of physical layer engineering and performance monitoring.

• The regenerators have to be deployed on the node output ports to extend the physical reach of the signals.

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Node Architectures A B C D E

Degree of wavelength conversion

Full

(DCS)

Full

(OXC)

Shared Partial None

Wavelength Blocking NO No No No Yes

# of cross-connects 1 1 1 1 W

Add/drop cross connects required

No No No No Yes

Routing and wavelength assignment

Simple Simple Complex Complex complex

Physical layer network engineering

Node-to-node

Node-to-node

End-to-end

End-to-end

End-to-end

Blocking fairness w.r.to hop length

good good good good poor

* Assuming sufficient WCs provisioned

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Acronyms

DCS – Digital cross connect

OXC – Optical cross connect

TWC - Tunable wavelength converter

FWC –Fixed – output wavelength converter

W – Number of wavelengths per fiber

F – number of fibers

P {p=P/W} – Arrival rate through demands

A {a=A/W} – Arrival rate of local add demands

{ Fractional Rate}

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Node Architectures

• A network built without any wavelength converters are best for localized demand patterns , because the wavelength continuity affects long demands (in hop count) much more severely than in short ones.

• Limited conversion designs use single large OXC with very few converters than in full-conversion case, but requires sophisticated network management.

• In another architecture, electronic wavelength conversion is performed at local access station in such a way that transmitters and receivers are shared by add-drop traffic and traffic requiring conversion.

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Wavelength Flexibility in the networks

• Wavelength Blocking --- Important parameters affecting blocking is the number of hops covered by a typical light path and blocking is nil in single hop and likewise little in short lightpaths.

• Although the hop count is larger in ring networks, wavelength blocking is less under probabilistic model, because there are strong correlations between the wavelength occupancies on adjacent links.

• Wavelength blocking is significant in networks with long lightpaths and low interference lengths, such as torus networks.

• If static demands are to be routed with off-line computation, wavelength blocking is typically reduced.

*** No. of links shared by an interfering demand averaged over all interfering demands

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Limited wavelength conversion

• How Much wavelength conversion is sufficient ? Although the details vary with the topology and traffic model, in

general, the answer tends to be that the level of wavelength conversion required is small relative to the full conversion.

In worst case ring analysis --without WCs –Require 2W with full WCs --- Require W

If equipped with simple, Fixed near neighbor wavelength conversion at a simple node -- Require W +1

The number of WCs required to eliminate the wavelength blocking depends on the routing and wavelength assignment algorithm used.

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Analytical Estimate of Converter Requirements

• The number of WCs needed in the network depends on the wavelength assignment algorithm used and trellis-based method is the best.

• Random Local wavelength assignment.• Though its simple, the analysis identifies a

number of qualitative factors affecting limited share conversion and gives an upper bound on the number of converters needed by other methods.

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Analytical Estimate of Converter Requirements

• An analogous algorithm was analyzed in the context of synchronous optical packet switching, using a large deviations approach.

• Developed some simple fluid model approximations to determine how many WCs are needed at a given node using random wavelength assignment.

• The results overestimate the number of converters needed as compared to the other methods.

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Analytical Estimate of Converter Requirements

• The upper bound will be loosest for very sparsely networks, such as rings, because the algorithm doesn’t take full advantage of high interference lengths.

• Traffic demands arrive at times specified by a homogeneous Poisson process and each demand has a fixed (link and node) route.

• If the demand cannot be give a wavelength assignment then it is blocked and disappears.

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Analytical Estimate of Converter Requirements

• The number of converters actually provisioned can be chosen to keep the probability that all converters are occupied below the given blocking threshold.

• The number of new demands that arrive during the average holding time in particular plays an important role.

• The dynamic model broadly tries to capture the variability arising from all the effects, without being tied to a particular time scale.

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Single input and output Fiber

• P= rate of demands passing through the node.• A = Total number of demands being added.• Let mean holding time is 1 time unit.• X = active through light paths using converters.• Z = active light paths that are added locally.

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Single Input fiber, Multiple Output Fibers, Single output Link

• The need for wavelength conversion can be greatly reduced.

• A channel is chosen randomly among the available wavelengths when connections are locally added and connections must be converted.

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Multiple Input Fibers, Single Output Link.

The through traffic from other fibers are randomly distributed on the output fiber in the same way as the add traffic, regardless of whether or not this through traffic uses conversion.

Similar description is done for multiple input and multiple output links.

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Maximum Number of Converters needed

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The analysis presented previously allows to determine design parameters for an optical node with limited wavelength conversion under random local wavelength assignment.

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• For full conversion (OXC-based) shared conversion, and partial conversion , the number of ports required grows roughly linearly with the total load.

• Discrete jumps occur at points where a new fiber must be added to one o f the links surrounding the node.

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For NODE 2

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Implementation

• The digital cross-connect switches and optical electrical optical conversion forms the basis of the full conversion design.

• The principle challenges for the nodes are limiting the cost and power consumption of the node as the bit rates and aggregate capacities in the network increase.

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Implementation

• Mesh nodes with single fiber links and tens of wavelengths per fiber require cross-connects with 50-200 ports.

• Optical switches based on MEMS beam-steering technology appear to be the most viable solution.

• One of the primary relationships in the design of beam-steering cross-connects is that between the number of ports and the physical size of the switch.

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Considerations

1. The beam spots must be physically separated on the micromirror array.

2. To maximize the port count, “D/s” should be made as large as technologically feasible.

3. The micromirror diameter "d" should be chosen at least 1.5 times larger than the spot size “D”, in order to minimize clipping losses on the mirrors and protect against small alignment errors.

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Conclusion

• Benefits of the wavelength flexibility in the network 1.Improved network capacity 2.Improved fairness or the multi-hop demand.

Disadvantage: This need for WCs and large cross connects.

• Although wavelength flexible node in the current networks typically used digital cross-connects and OEO conversion, the analysis shows that design on all optical is also feasible.

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Conclusion

• Optical degree of the wavelength flexibility depends on many factors.

a. Network topology

b. Traffic assumptions

c. Network management considerations.• The relative costs of the cross-connects, WCs

and the line systems are more important to determine the degree to which wavelength blocking may or may not be tolerated.

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Discussion