Istanbul

1
Some Modeling and Simulation Problemsrelated
toswitching in all-optical networks
Ercan Topuz Istanbul Technical University
2
Switching in Optical Networks

• Circuit Switching
• Optical Internet
• Optical Burst Switching (OBS)
• OBS Modeling Simulation
• Conclusions

3
Circuit Switching

• As traffic increases rapidly in the Internet WDM
  optical networks become a natural choice for the
  backbone.
• Speeds in the order of Tb/s have been
  demonstrated with Dense Wavelength Division
  Multiplexing (DWDM) techniques to provide ca. 100
  Light Paths (LP Wavelength Channel) on a single
  fiber each carrying data at 10-20 Gb/s.
• Current systems employ circuit switching in the
  optical domain. LPs between end users are
  established via Optical Add-Drop Multiplexers
  (OADM) and Cross-Connects (OXC).

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Circuit Switching ctd.

• N fibers, M LPs

.......
Switch Fabric
.......
O E
O E
Drop
Add
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Circuit Switching ctd.

• Optical-Electrical-Optical (O-E-O) Conversion at
  each node.
• Fine grain processing in the electronic domain.
• Advantages
• Fresh copy generated at each node.
• Full QoS Management capability.
• Disadvantages
• Dependence on speed/protocol (Opaque).
• Inefficient utilization of resources.
• Speed limitations imposed by available electronic
  processing capabilities.

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Optical Internet

• IP-over-WDM seems promising
• IP provides common platform for services
• WDM offers almost unlimited bandwidth and
  throughput

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Optical Internet ctd.

• OPTIONS
• Optical Packet Switching (OPS).
• Optical Burst Switching (OBS).

Packet Switching
Burst Switching
Wavelength Switching
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Optical Internet ctd.

• LIMITATIONS
• 1. Optical Processing techniques at
  sub-wavelength granularity and high speed have
  not yet matured
• 2. Optical buffering.
• Common approach is to use fiber delay lines
  (FDL)
• Bulky (100m fiber for delaying a packet of 10kb
  at 20Gb/s)
• Inflexible (A tree of FDL required for step-wise
  control)
• Random access not possible.
• PRESENT STATUS
• OPS at early experimental stage Dorren H.J.S.
  et.al, IEEE, JLT Jan.2003, pp.3-12.
• OBS several versions successfully demonstrated
  http//www.utdallas .eduvinod/obs.htm .
  Near-Mid term implementation feasible.

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Optical Burst Switching

• ADVANTAGES
• Transparent
• Efficient utilization of resources
• DISADVANTAGES
• Faces two technological bottlenecks Processing
  speed and buffering.
• Noise accumulation
• No/limited QoS management.

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Optical Burst Switching ctd.
Differentiate between Edge Nodes and Core Nodes
Edge Nodes - Electronic processing. Combine
packets (common destination/priority etc.) to
form bursts. Control data sent over different
channel with time offset. Core Nodes -Fast
optical switching with l conversion One pass
reservation Buffer not inherently needed.
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Optical Burst Switching ctd.
OBS Architecture
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Optical Burst Switching ctd.
Advantages

• Decoupling of header processing and data
  forwarding
• allows sophisticated processing of control
  information,
• data can stay in optical domain resulting in
  high throughput,
• transparent independent of client layer.
• One-pass reservation saves time and bandwidth
• Scalability and flexibility by sharing of
  wavelengths
• QoS support in the optical layer

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Optical Burst Switching ctd.
Service Differentiation
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OBS Modeling Simulation
Control and data channels can be modeled
separately
An example Simulation of Optical Burst
Switching Protocol and Physical Layers , A.
Louridas,et.al. OBS network using the
Just-Enough-Time (JET) protocol model is created
by implementing multiple simple n-channel network
models in OPNET Modeler. The Physical Layer
performance of an OBS network is investigated
using VPItransmissionMaker, and performance
predictions based on realisable technology and
dependent on parameters such as distance between
nodes and number of nodes are obtained.
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OBS Modeling Simulation ctd.
PROTOCOL IMPLEMENTATION OF OBS
Simulation model of a core node in a
Burst-Switched network.
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OBS Modeling Simulation ctd.
OBS PHYSICAL LAYER MODELLING
OBS network Physical Layer representation in VPI
Systems software one optical core node
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OBS Modeling Simulation ctd.
OBS network Physical Layer representation in VPI
Systems software one optical core node
Received eye diagrams for two scenarios.
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Optical Burst Switching ctd.

• Hybrid techniques can be used to cut down
  simulation time
• An example An effective Method for Blocking
  Performance Analysis of WDM All-Optical Networks,
  J.Xiong, et.al, IEEE JLT, June 2003,
  pp.1421-1435.
• Step 1 - A parametric representation in the form
  of a rational approximation function is derived
  for the blocking probability in wavelength routed
  optical networks.
• Step 2- The parameters of the function are
  determined using DES for (unrealisticaly) high
  blocking probabilities (BP). (
• Step 3- Validate via few DES runs in the low
  BP region.

Fast )
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Conclusions

• All Optical Networks (OAN) utilizing OPS and OBS
  will most probably be implemented in near future
  as backbone networks.
• OAN presents challenging modeling and simulation
  problems
• Very high data rates (Tb/s)
• Large networks
• Hybrid approaches needed (COST 285 ?)

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THANK YOU