24 Lecture Wosinska

8/2/2019 24 Lecture Wosinska

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Photonics in Switching

Lena Wosinska, Assoc. Professor

Royal Institute of Technology KTH

Electrum 229, 164 40 Kista, Sweden

[email protected]

The aim of this tutorial

To s ow princip es or optica circuitswitching and optical packet switching

To highlight the main technologicalproblems

Krakow Sept. 29, 2009 L. WosinskaTutorial at BONE Summer school 2

To give some examples of the opticalswitching node architectures


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Outline

Introduction

Photonic Circuit Switching WDM network design

WDM network elements

Photonic Packet Switching

Krakow Sept. 29, 2009 L. WosinskaTutorial at BONE Summer school

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Contention resolution

Summary

How to connect end users ?


4


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Switched networks

Switching nodes not concerned with contents

of data purpose: provide switching

facility in general not fully connected

End nodes provides data to transfer

1

A


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nodesLinks

physical connections betweennodes

Switching

Circuit

Switching

Packet

Switching

Switching


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Connection Oriented

(Virtual Circuit)

Datagram


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Development ofoptical networks

First-generation optical networks

Transmission in the optical domain (to provide capacity)

Example: SONET network (Synchronous Optical Network)

Second-generation optical networks

More functionality in the optical domain (optical networking)


Some of routing, switching and intelligence is moving into theoptical layer

Third-generation optical networks (?)

SDH/SONET Networking


8


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Photonics in switching

O tical circuit switchin OCS Wavelength-routed networks

Relatively mature technology today

Providing lightpaths

WDM network elements: OLT, OADM, OXC

(All)optical packet switching (OPS) Not available today due to some technological problems


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on ro a e op ca memory or op ca u er ng Control functions in the optical domain

Synchronization, etc

Optical burst switching (OBS) A feasible solution?

Optical Circuit Switching

W ave leng th -Rou t ed Ne tw o rk s


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-

Wavelength-RoutedNetworks

Provide lightpaths

Problems:

Low bandwidthefficiency

Large granularity

Network


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1

A

Wavelength-routing switch

Access (client) node (e.g., IP router):

contains (tunable) transmitters and receivers

Optical circuit switching

Solvin LTD and RWA roblems

A lightpath corresponds to a circuit

Set-up a lightpath

The whole lightpath is available during the connection Disconnect

Network elements

Fiber


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Optical line amplifier (OLA)

Optical line terminal (OLT)

Optical add-drop multiplexer (OADM)

Optical cross-connect (OXC)


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Definitions

Logical (virtual) topology

Physical topology: Fiber topology


Kind of time multiplexing: packing a low speed

channels into higher speed channels.

ObjectiveSeattle

New York


Given a traffic matrix (a forecast) and a fiber (physical) topology:design the networkthat fits the traffic forecast or/andoptimize the (existing) network


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Network design

the fiber (physical) topology and

traffic matrix (obtained by forecasting): in packets/second

Determine

the lightpath (virtual or logical) topology (Lightpath topologydesign: LTD): grooming


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physical routes through the network and wavelengthassignment (RWA): map the LTD into the physical topology

Heuristic solution

ar to eterm ne t e g tpat topo ogyjointly with the routing and wavelength

assignment Split into separate LTD and RWA problems


obtained LTD within the optical layer (i.e. for theobtained LTD solve RWA problem).


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LTD:Lightpath topology design

ven: The traffic demands

The maximum number of ports per client node

Lightpaths interconnect client nodes bidirectionally

Determine the topology and routing of packets


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Objective (an optimization problem): Minimize the maximum load that any lightpath must

carry

RWA:Routing and wavelength assignment

to the fiber topology

Objective

Offline: for all lightpaths determined by the

LTD minimize the number of wavelen ths


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used per link

Online: for demands coming during

operation minimize the blocking probability


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RWA approaches

Heuristic Routing sub-problem

Wavelength assignment sub-problem


Routing sub-problem

Fixed shortest-path routing

Fixed-alternate routing Routing table at each node that contains a list of

fixed routes to each destination


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The route is chosen dynamically, depending of the

network state

Fault-tolerant routing


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Routing algorithms

Shortest Path selects the shortest source-destinationpath (# of links/nodes)

Least Loaded Routing avoids the busiest links

Least Loaded Node avoids the busiest nodes


WA sub-problem

-

Graph coloring

Dynamic WA sub-problem Random (R) Wavelength Assignment

First-Fit (FF)


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Least-Use LU SPREAD

Max-Used (MU)/PACK

Least Loaded (LL)

etc.


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Static (offline) WA:Graph coloring

NC Wavelen th continuit constraint

Given: all connections and routes

Objective: assign wavelengths (colors) to each lightpath so as tominimize the number of wavelengths used under the wavelengthcontinuity constraint

Constr uct a graph G so that each lightpath in the system isrepresented by a node. Undirected edge between nodes in the


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G if the corresponding lightpaths share a physical link Color t he nods of G such that no two adjacent nodes have the

same color.

Dynamic (online) WAalgorithms

Random (R)

Pick one with uniform probability

First -Fit (FF)

All wavelengths are numbered Assign the first available wavelength

Least -Used (LU)/ SPREAD

Select the wavelength that is the least used in the network


Max-Used ( MU)/ PACKED

Select the most used wavelength in the network

Least- Loaded (LL) designed for multi-fiber networks

Select the wavelength with largest residual capacity on the most loadedlink along the connection.


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WDM network elementsWDM network example

Optical line terminals

(OLTs)

Optical add-drop

multiplexers (OADMs)


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p ca cross-connec s(OXCs)

Optical line amplifiers

OLT: Optical line terminal

Trans onders Adaptation from/to access

links Wavelength and fiber

Overhead and FEC BER monitoring

Main cost of OLT

Multiplexer To mer e the incomin


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channels

Amplifier (optional)

Optical supervisory channel(OSC) Added and terminated


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OADMOptical add/drop multiplexer

To and from equipment at local node

Remaining channels pass transparently

Channel selecti on

Any channel or only some


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Reconfigurable: software configurable remotely

One, a few or any number of channels Modularity

Loss dependence on number of dropped channels

OXCOptical Cross-connect

From input to output ports

From input to output wavelengths

Does not include input/output OLTs

Functions


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Protection switching (rerouting)

Performance monitoring

Wavelength conversion


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Types of OXCs

Transparency

Cost

Size

Transparent or opaquecore


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Electronic signal

Signal monitoring

Optical signal

Transparency

All-optical OXCs

Grooming

Higher demand for lightpaths No aggregation of low bitrate demands

Wavelength conversion


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g er oc ng o g pa eman s

Signal regeneration More constrained routing of lightpaths


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All-optical OXCEx. 1: Clos architecture


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Three stage strict internal non-blocking Clos architecture.

Size: 128x128

L. Wosinska, L. Thylen, and R.P. Holmstrom: Large Capacity Strictly Non-Blocking OXCs Based on MEOMS

Switch Matrices. Reliability Performance analysis, IEEE/OSA JLT, Vol.19, No.8, Aug. 2001

All-optical OXCEx. 2: WR architecture


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Strict internal non-blocking wavelength routing architecture.

Size 128x128

L. Wosinska L. Thylen, and R.P. Holmstrom: Large Capacity Strictly Non-Blocking OXCs Based on MEOMS

Switch Matrices. Reliability Performance analysis, IEEE/OSA JLT, Vol.19, No.8, Aug. 2001


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All-optical OXCEx. 3: with TWC


33J. Chen, A. Jirattigalachote, L. Wosinska and L Thyln, Novel Node Architectures for Wavelength-Routed WDMNetworks with Wavelength Conversion Capability, in Proc. of ECOC08, Brussels, Belgium, September 2008

Performance evaluation


34J. Chen, A. Jirattigalachote, L. Wosinska and L Thyln, Novel Node Architectures for Wavelength-Routed WDMNetworks with Wavelength Conversion Capability, in Proc. of ECOC08, Brussels, Belgium, September 2008


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Shortcomings with OCS

Low utilisation of resources

Hard optimization problems need to be solved

(LTD and RWA)


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Solution: Optical Packet Switching (?)

Optical packet switching


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OPS Networks

Large capacity

High bandwidth efficiency

Rich routing functionalities

Great flexibility andreliability


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Optical packet switching

Advanta es Complements WDM

Allows grooming in optical domain

Allows statistical multiplexing

Can improve bandwidth utilization within the optical layer

Increase flexibility

Problems


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Technological problems

Optical control functions

Synchronization

Optical buffering

High complexity of OPS nodes high cost and low reliability


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Optical router (OPS node):Needed functions.

Decoding of packet header Could be electronic: header encoded at lower bit rate

Setup of switch fabric Packet delayed until setup done (a fixed delay)

Setup requires scheduling of packets from all inputs Simplified for fixed packet size and synchronized operation

Fast reconfiguration of fabric (200 ns for 250 byte packet at 10 Gb/s)

Synchronization: Elastic buffering of packets to align packets at all inputs


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n y nee e w en sw c a r c s sync ronous Synchronous fabric has better throughput

Multiplexing of lower-speed streams (and reverse operation, i.e.demultiplexing)

Contention resolution (e.g. buffering of packets if output busy)

Contention resolution in OPS

Contention may be dealt with in

Time

Wavelength

Space

Electronic packet switching typically rely on the time


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domain by means of queuing

What about optical packet switching ?

Queuing in optical domain is difficult


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If output busy:Handling packet contention Drop a packet

r y v r

Deflect the packet Send it on a free output

Restrict the deflection Output that leads to destination

Output with a route to the destination that is at most mhops longer

Also called hot-potato routing

Increases delay and network load

Creates variable delays and potentially reordering


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C ange t e wave engt TWC Chose a wavelength available at the output

All-optical tunable wavelength converters not available yet

Buffer the packet

Store the packet until the output is available

Applying TWC may allow for decrease of the buffer size

Contention resolutiontechniques

Bufferless architecturesOCIC

e ec on rou ng

TWC

Electronic buffers

Optical buffers Placement at a node

Output buffer

Input buffer

switchfabric

OC

OC

IC

IC

switchfabric

IC

IC

IC

OC

OC

OC


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ec rcu a on u er

Dedicated or shared buffers

Technology

FDLs

Novel optical memories

EIT or Opt. resonators

buffer


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OPS with electrical buffer


L. Wosinska and G. Karlsson, A photonic packet switch for high capacity optical networks, in Proc. NFOEC02, Dallas,Texas, September 2002

COMPARISON

Architecture I II

Buffer Dedicated Shared

Packet loss probability High Low


Scheduling Simple Complex



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Comparison. N=20



A2A1

Optical buffering

Fiber delay lines (FDLs)

Not random access

Require synchronization

Supported packet format Constant packet size

Some configurations support variable packet size A certain granularity

Not compatible with packet formats of different packet size

Long fiber delay lines Not very practical solution

Ex.: For packets containing 53 bytes (ATM cell) at 2.5 Gb/s the length of fiber in the FDLs needs


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to be the multiples of 640 m

Feed-forward or feed-back configurations

Novel solutions for optical memory

Material subjected to EIT (Electromagnetically induced transparency)

Optical Cavities


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1 km

Fiber delay line

Cheap and easy to manufacture

Several kilometers long

-


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No flexibility in terms of storage time

Requires synchronization

Many architectures proposed to introduce variabledelay

EITNovel type for optical memory

artificially created spectral window of transparencyused to slow and spatially compress light pulses.

Inside the memory cell, light is converted into a spinexcitation of atoms and its velocity drops down tozero once the coupling beam is turned off. After the


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coherence is converted back into light signal.


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EIT, cont.

beam


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Memory cellArriving IP packet

Optical fiber

EIT, cont.

Phase 1 : w r i t i ng


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Light slows down inside the cell andis spatially compressed


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EIT, cont.

Phase 1 : w r i t i ng


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Cell length

The memory cell needs to be long enough to fit the entire packet

IP packet of 1500bytes at 2,5Gb/s is 1,4 km long in free space andabout 1km long in an optical fiber

EIT, cont.

beam is turnedoff

Phase 2 : s tor age


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The light is stored in the material


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EIT, cont.

beam is turnedback on

Phase 3 : read in g


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The light is recoveredand leaves the cell

EIT, cont.

Variable couplingpower


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No storage of light

We regulate the slowdown factor by varying the coupling power

The packet is slowed down in the cell


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EIT, cont.

material slow dow n factor storage t ime

Quantum dots 40 in room temperature

107 in very low temperature

8.7ns

Atomic vapor 105 up to 0.5 msdepends on thegas


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Slow down factor and storage time depend on thematerial, temperature, coupling power, bandwidthand wavelength

Optical cavities use optical resonance in photonic structures

Optical cavities

Slow down factor of 104 (depending on the number ofside cavities)

Storage time: 50 ns

Chip scale implementation of the system foreseeable


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Requirementsfor optical memory

Technology Compression rate (cell size) Tuning of the intensity of thecontrol field Temperature and mechanical stress Cost

Te lecommun ica t ions Wavelength Attenuation anddistortion Bandwidth Packet length Control memory cellsseparately


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Qo S The storage time Pulse distortion Priority classes

Comparison

storage t ime cell size temperat ure bandw idt h-wavelength

EIT

Up to 0.5 ms Order of cm Close to 0K or80C

Depends on thematerial


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Opticalcavities

Order of ns Size of a chip Room temp. No limitations


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Parallel electricaland optical buffer

Example 1:OPS with hybrid buffer.

positions

Opticaloutputs

Opticalinputs

Opticaldemultiplexer

Switchingmatrix


59L. Wosinska, J. Haralson, L. Thyln, Benefit of Implementing Novel Optical Buffers

in an Asynchronous Photonic Packet Switch, in Porc. ECOC04, Stockholm, Sept. 2004

ASSUMPTIONS The traffic load is uniformly distributed between the outputs.

The traffic load at all inputs is identical.

.

.

.

1

N

1

B u f f e r

1

.

.

.


The transparency class (i.e. packets that can not beconverted to the electrical signal) represents 20% of the totaltraffic

N + N

.

.

.

.

.

.

N

N + 1

N

L. Wosinska, J. Haralson, L. Thyln, Benefit of Implementing Novel Optical Buffers



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Without output buffer,N > 16

Packet loss probability

0 3 5

0,37

0,39

0,41

0,43

0,45

,


0,31

0,33

,

0,4 0,5 0,6 0,7 0,8 0,9 1

load

simulated, const. packet l ength simulated. IP-traffic calculated



IP traffic trans arenc class

Simulation results.IP traffic.

1,E-02

1,E-01

1,E+00

packetlossp

r

obability

load 0.2

load 0.5

load 0.7


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The loss probability goes down to a certain point and thanstays constant as the buffer increases.

1,E-03

0 2 4 6 8 10 12 14 16

number of optical buffer positions




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ATM traffic, transparency class

Simulation results.ATM traffic.

1,E-06

1,E-05

1,E-04

1,E-03

1,E-02

1,E-01

1,E+00

loss

probability

3 buffer positions5 buffer positions10 buffer positions


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The lowest achievable packet loss probability for a givennumber of buffer positions reaches a limit that cannot beovercome by increasing the maximum storage time.

0 0,05 0,1 0,15 0,2 0,25

maximum storage time in s



ATM traffic, trasnparency class

Simulation results.ATM traffic.

1,E-06

1,E-05

1,E-04

1,E-031,E-02

1,E-01

1,E+00

packetloss

pro

bability load 0.2

load 0.5

load 0.7


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Storage time of 0.5ms is enough to obtain any value of lossprobability for any traffic load.

0 2 4 6 8 10 12

number of optical buffer positions




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Example 2:OPS with TWCs and buffer


65JiaJia Chen and L. Wosinska, Novel Architectures of Asynchronous Optical Packet Switch, in Proc. of EuropeanConference on Optical Communication ECOC07, Berlin, Germany, September 2007

Evaluation


66JiaJia Chen and L. Wosinska, Novel Architectures of Asynchronous Optical Packet Switch, in Proc. of EuropeanConference on Optical Communication ECOC07, Berlin, Germany, September 2007


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Summary Switched networks

Photonic circuit switching WDM network design: solving offline LTD and RWA

Objective: minimize number of wavelengths

Dynamic scenario

Oblective: minimize blocking probability

WDM network elements

Photonic packet switching


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Makes networks more efficient Many technical challenges for switch design

Buffering for contention resolution

Scheduling for contention resolution with possible deflection

Switching speeds


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