A Presentation on Design and Implementation of Wavelength-Flexible

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					                        A Presentation on

 Design and Implementation of
 Wavelength-Flexible Network
Carl Nuzman, Juerg Leuthold, Roland Ryf, S.Chandrasekar, c. Randy
                    Giles and David T. Neilson

                      Sudharshan Reddy .B

• What is this presentation about ?
• Node Architectures
• Wavelength flexibility in the networks
• Analytic Estimate of Converter
• A brief discussion on Implementation
• Conclusion
What is this presentation about?
• Analytically and Experimentally examination
  of node architectures for wavelength routing
• 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.

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.
            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)                        5
          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.                                    7
                Node Architectures
                                  A           B           C        D         E
Degree of wavelength         Full         Full       Shared    Partial   None
conversion                   (DCS)        (OXC)
Wavelength Blocking          NO           No         No        No        Yes

# of cross-connects          1            1          1         1         W

Add/drop cross connects      No           No         No        No        Yes
Routing and wavelength       Simple       Simple     Complex   Complex   comple
assignment                                                               x
Physical layer network       Node-to-     Node-to-   End-to-   End-to-   End-to-
engineering                  node         node       end       end       end
Blocking fairness     good         good       good      good      poor
hop length
             * Assuming sufficient WCs provisioned
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
               { Fractional Rate}          9
           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.

       Wavelength Flexibility in the
• 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
• 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   11
 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.

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

Analytical Estimate of Converter
• 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

Analytical Estimate of Converter
• 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.

Analytical Estimate of Converter
• 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.

    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.
   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
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.

Maximum Number of Converters

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

• 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.

For NODE 2

• 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.
• 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
• 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


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

Disadvantage: This need for WCs and large cross
• 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.        27
• 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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