A Presentation on Design and Implementation of Wavelength-Flexible Network Nodes

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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 WCs
  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 (OXCs) 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 pP/W Arrival rate through demands
• A aA/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
  doesnt 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

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