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Optical Networking: Optical Networking: Principles, Hot Topics Principles, Hot Topics

and Future Perspectivesand Future Perspectives

November 24November 24

Sébastien RumleySébastien Rumley

EPFL – EPFL – Laboratoire de Laboratoire de Telecommunication Telecommunication (TCOM)(TCOM)

sebastien.rumley@epfl.chsebastien.rumley@epfl.ch

TCOM

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Outline• 1. Optical networking : principles

– Optical transmission (history, rules of thumbs, etc.)

– Optical switching

– Context and challenges

• 2. Research fields– Components

– Network Management schemes

– Optical networks design and planning• Routing and Wavelength Assignment (RWA)• Routing and Regenerator Placement (RRP)• Optical Burst Switching

• 3. Alternative ideas– All Optical Network Coding

– OBS multicast

– Ad-hoc wireless optical networks

Technological research

Academic research

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Principles : Optical transmission

• An optical fibre is a wave guide.

• The light emitted by a laser diode is modulated and injected in this guide

• The modulated signal is analysed with a photodiode at the fibre end

Fibre (wave guide)

Laser + modulation

Input data

Photodiode

Output data

• The transmitted signal is subject to

– Attenuation (bending, absorption, scattering)

– Impairments (chromatic dispersion, polarisation, non-linear effects…)

Impairments Noise

Attenuation + noise Signal to Noise Ratio (SNR) !

Absorption/ScatteringBending losses

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Raw transmission limits

1. The attenuation is frequency dependent– A fibre is a very good wave guide for given frequencies only

– Typically in three “windows” located around 1.4 μm– Outside, light is attenuated by various effects

2. Modulation speeds– In theory, bandwidth of ~2x20 Thz

~80 TBaud/s (Nyquist)– Not realisable in practice

3. Impairments:– Non linear effects– Chromatic dispersion

Image source : http://www.fiberoptics4sale.com/wordpress/optical-fiber-attenuation/

This profile is different for each fibre

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Transmission enhancement : multiplexing

• Multiplexing of independent channels (λ), modulated at lower rates WDM (Wavelength Division Multiplexing)

Good news :• Capacity multiplied

Bad news :• Crosstalk

Noise

• Demultiplexing losses Attenuation

Image sources : http://www.imec.be/ScientificReport/SR2008/HTML/1225202.htmlhttp://www.harzoptics.de/pof-demultiplexer.html

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Trans. enhancement : optical amplification

• How to mitigate the attenuation?• How to carry signals over longer distances?

By reamplifying them !

• Electronic amplificationDemodulate the light signal with a photodiode, remodulate a new signal

+ Not only amplification (Resizing), but also Retiming and Reshaping (3R)- Resource and energy consuming- With WDM, demultplexing and remultiplexing is required- One regeneration per signal

• Optical amplificationSimilar principle as the laser

+ All channels amplified simultaneously- Amplification only- Works only for given frequencies

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Historical landmarks for transmission

• 1) Point-to-point links with electrical regeneration (70’)

• 2) Point-to-point links with multiplexing - WDM (80’)

• 3) Point-to-point WDM links with optical amplification (90’)

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Recent advances on transmission

• QAM modulation– 1.568 Tbit/s with a 16-QAM [1]

– Spectral efficiencies > 6 b/s/Hz

• More channels – 500 channels (25 Ghz channel spacing) [2]

• Faster modulations– 640 Gbit/s [3]

[1] Xiang Liu, Sethumadhavan Chandrasekhar, Benyuan Zhu, Peter Winzer, David Peckham “7 x 224-Gb/s WDM Transmission of Reduced-Guard-Interval CO-OFDM with 16-QAM Subcarrier Modulation on a 50-GHz Grid over 2000 km of ULAF and Five ROADM Passes“, ECOC 2010[2] Chun-Ting Lin, “400-Channel 25-GHz-spacing SOI-based planar waveguide demultiplexer employing a concave grating across Cand L-bands”, Optics Express, Vol. 18, Issue 6[3] Hao Hu, Evarist Palushani, Michael Galili, Hans Christian Hansen Mulvad, Anders Clausen, Leif Katsuo Oxenløwe, and Palle Jeppesen, “640 Gbit/s and 1.28 Tbit/s polarisation insensitive all optical wavelength conversion”, Optics Express, Vol. 18, Issue 10

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Optical switching and optical regeneration

• With these througputs, (< 10 Tbit/s) we have pleanty of leeway at the transmission level

• What are the next steps ?

• Optical switching– Available

• MEMS• Filters• Other

• Optical regeneration– Not available (yet?)

Image sources : http://www.fiberopticsonline.com/article.mvc/Alcatels-new-OXC-leverages-bubble-technology-0001https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr200710sp5.html

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Optical switching• Per channel (lightpath) switching – Optical Circuit Switching (OCS)

After demultiplexing, deflect a wavelength in a particular direction

+ The easiest way

+ Can be done manually and statically

- Low granularity

- More generally… low flexibility

• Sub channel switching – Optical Packet/Burst Switching (OPS/OBS)After demultiplexing, deflect a wavelength in a particular direction for a given

duration

+ Finer granularity, more flexibility

- Network Control overhead

- Switching time overhead

- More complex network Management

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Optical networks applications

• Intra-office communications• Fibre to the home• Application specific (e.g. CERN)

• Long-haul networks– Range up to 5’000 km or more

– Traffic demands ~ 100 Gbit/s per node pair

– Intra domain communications no more than ~100 nodes

– High Availability (six nines 99.9999% 30 sec per year)• One second of unavailability at 1 Tbit/s = 1 Terabit of lost…

– High investments

Not in the scope of this talk

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Optical networks – goals and challenges

GOALS :

• Above all: deliver bits– High throughput– High availability– Low congestions– No errors

• Minimize the costs– Energy– Investments– Maintenance

• Minimize the risks– Network must be under control– Capacity must be available

CHALLENGES :

• Improve network utilisation– Reduce the cascaded

overprovisionning– Minimize the frequency « trap »

• Reduce energy consumption– Avoid per bit operations– Rationalise the utilisation

• Improve network management schemes

– Without adding too much complexity– While guaranteeing availability

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2. Research in optical networks• Components

– Fibres

– Lasers/modulations

– Multiplexers/demultiplexers

– Amplifiers

– Cross-connects

• Network design and planning– Resources provisioning

• Network design

– Resources allocation• Network planning

• Network orchestration– Remote operation

– Computer aided management

– Configuration automation

+

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Routing and Wavelength Assignment - RWA

Most famous optical network problem

Network design version

• Given: – a matrix of demands (# lightpaths required

between each source-destination pair)

• To find: – Network capacities

– a route and a wavelength for each lightpath

• Constraints:– A lightpath must keep the same wavelength

all the way long

– Two lightpaths cannot share a fibre if they use the same wavelength

• Objective:– Minimise the required wavelength

– Minimise the number of required fibres

Network planning version

• Given: – a matrix of demands

– A list of capacities (fibres and λ)

• To find: – a route and a wavelength for each lightpath

• Objective:– Minimise the rejected demands

– Minimise the “frequency traps”

– Minimise the required wavelength

– inimise the number of required fibres

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RWA – more variants

• In the network planning version, the demands may– Arrive

• Simultaneously• At different time points

– Begin• Immediately• Later in time (delayed)

– Last• Forever (open end)• For a fixed duration

• Design + Simultaneous + Immediate + Forever colouring problem• Planning + Simultaneous + Immediate + Forever bin packing [4]• Planning + Simultaneous + Delayed + Fixed duration scheduling [5]

[4] N. Skorin-Kapov, “Routing and wavelength assignment in optical networks using bin packing based algorithms[5] X. Liu, C. Qiao, et al. “Task Scheduling and Lightpath Establishment in Optical Grids

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RWA – event more variants

• Impairments constrained RWA– RWA that takes into account the signal quality and inter wavelength

perturbations [6]

• Protection aware RWA– Both main and spare path must be found– Dedicated or shared protection

• Multi priority RWA

• Multicast aware RWA

• Etc.

[6] A. Marsden, A. Maruta, K.-I. Kitayama, “Routing and Wavelength Assignment Encompassing FWM in WDM Lightpath Networks

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RWA – Solving methods

• ILP / MILP• Constraint Programming• Heuristics

– ILP Relaxation

– Tabu search

– Greedy

– Simulated annealing

– ….

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Routing and Regenerator placements

• Optical signal must be regenerated after a certain journey• Regenerators must be installed

– However, regenerators require more power, more space, more complex chassis, more maintenance

– They should be placed only in strategic places

Problem : minimise the network's critical length (if not fixed)

minimise the number of equipped nodes

minimise the number of regenerations

minimise the routing costs

a

b

c d

ef

g

a-c-b

a-c b-c

a-c-d b-c-d c-d

a-e b-c-a-e c-a-e d-f-e

a-e-f b-c-d-f c-d-f d-f e-f

a-c-g b-c-g c-g d-g e-f-d-g f-d-g

CL=1

CL=2

CL=3In this example, two solutions to reduce CL:

A) Add a regenerator in d

B) Reroute e-f-d-g e-a-c-g

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Problem – Conflicting Objectives

• Minimize the routing shortest paths taking no detours More regeneration sites

• Minimize the # of regenerations shortest path… in most cases

• Minimize the sites oblige lightpath to take detours More regenerations and more routing costs

S

a b

x

c d e

1010 10

88 8

8S

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a d

c f

b eb

c

d

f

e

(a) Regenerations : 3Routing cost : 3x(8+5+5) = 54

(b) Regenerations : 5Routing cost : 2x(8+5+10) + 18 =

64

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Multi-objective optimisation

0 0.25 0.5 0.750

5

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30 n

odes

C1

pena

lty (

in %

)

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odes

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pena

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Relative optical reach

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Optical Burst Switching

• General problem of Optical Circuit Switching (of circuits in general) :– A customer of a long-haul operator requires capacity for a fixed duration

– He measures demand peeks of 60 Gbit/s

… whereas the average demand is ~5Gbit/s He nevertheless orders a 30 Gbit/s connection

Overprovisioning factor : 600%

– The operator has many customers

– In general, 25% of them ask for connection

… but sometimes 75% of them The operator is required to design its network accordingly

Overprovisionning factor : 300%

Most of the time, a sixth of a third of the capacity is used… ~5%

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Optical Burst Switching – Statistical multiplexing

• General idea :– With OCS, the operator cannot look “inside” a circuit and fill the voids

– Idea: • Offer to the customer to carry its small packet directly (e.g. IP packets)• Schedule them himself in the network

– Problems:• IP packets are too small to be inserted independently in the optical network• Reserve a circuit for these packets ? Back to the original problem• Multiplex statistically at network edge ?

– Require huge routers (avoid per bit operations ?)– Require to centralise the entering packets (rationalise utilisation ?)

– Solution:• Aggregate in edge nodes smaller packet until reaching an adequate size• Let the network node cores multiplex these bursts

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OBS – General Assumptions

• Burst of about 1mbit – 0.1 ms at 10Gbit/s• Burst are sent in a cut-though manner

– No per bit operation along the way

• Burst are preceded by a Burst Control Packet (BCP) sent in advance– A dedicated lower bit rate channel is reserved for the BCPs

– The BCP “announces” the burst arrival at intermediate nodes

– One way reservation• If a node has no resources, the BCP is dropped, and the burst will be blocked

[7] C. Qiao, M. Yoo, “Optical Burst switching (OBS) – a new paradigm for an optical internet, Journal of high speed networks, 1999 – IOS Press

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OBS Variants

• Burst assembly mechanisms (fixed size, fixed delay, hybrid)• Conventional OBS vs. Emulated OBS

– In E-OBS, BCP and burst are emitted simultaneously• Burst are delayed at each core node entrance

• Reservation protocols– Explicit setup - Explicit release

– Estimated setup - Estimated release

• Scheduling algorithms– With or without void filling

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More OBS Variants

• Routing :– In general, try to minimize the resources consumption shortest path

– Sometimes, better to avoid congested zones• Pro-active routing scheme : load-balancing• Re-active routing scheme : deflection routing

• Synchronous or quasi-synchronous OBS

• Etc.

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QS-OBS : Performance analysis

[8] O. Pedrola, S. Rumley, et al. “Performance overview of the quasi-synchronous operation mode in optical burst switching (OBS) networks, Elsevier Journal of Optical Switching and Networking, Issue 8, In Press

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Contention in OBS

• Contention occurs when a burst cannot be forwarded on its natural path

• Among all the situations causing contention, one can highlight two extreme cases :

Statistical fluctuation – transient phenomenon – short term overload

"bad luck"

No fluctuation! - stationary phenomenon – long term overload

"misconfiguration"

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Contention avoidance methods

Connection Access Control (CAC)

Adaptive load balancing

Traffic engineering – load balancing

Redimensioning

Burst deflection

Flow smoothing and synchronisation

Buffering with FDL

Short term overload

Medium

term overload

Long term overload

Not viable economically

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Our goal

Integrate in one single scheme :

perform this scheme directly at the OBS layer

A Connection Access Control (CAC)

An adaptive load balancing

A burst deflection

Short

Medium

Long

Adaptive burst Admission and Forwarding

[9] S. Rumley, O. Pedrola, et al. “Feedback Based Load Balancing, Deflection Routing and AdmissionControl in OBS Networks”, Journal of Networks, Academy Publisher, Nov 2010

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e1

1

2

3

4

e55

In more detailsID :1-5:ac

ID :1-5:ac1

ID :1-5:ac1,3

- Burst Control Packet (BCP) carries an ID

- BCP contains a list of visited nodes

- When a BCP is dropped…

ID :1-5:ac1,3,4

… or arrives at destination

a feedback is sent to each node of the list

1-5:ac OK1-5:ac OK1-5:ac OK

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In more details

e1

1

2

3

4

e55

- BCP also store the remaining offset time and of course the destination index

- When a core node takes a forwarding decision it adds this decision in a local table (pending table)

- When a core node receives a feedback it retrieves the corresponding decision from the table and updates its feedback table

ID :1-5:acOff: 4Dest: e5 ID :1-5:ac

Off: 3Dest: e5

Next : 3 !

Pending table node 1

3351-5:ac

Next hopOffsetDestID

ID :1-5:acOff: 2Dest: e5

ID :1-5:acOff: 1Dest: e5

ID :1-5:acOff: 0Dest: e5

1-5:ac OK

……………

……………

00335

00212

-+NextOffsetDest

1

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Burst forwarding

e1

1

2

3

4

e55

ID :1-5:acOff: 4Dest: e5

6241335

5134235

-+NextOffsetDest

96.4 %

97.6 %

- When a BCP arrives, the core node retrieve the feedbacks corresponding to the destination and offset

- The success probabilities are estimated for each possible next hop

- Core node tries to make a reservation, starting with the highest probability

- If no reservation is possible on the most favorable next hop, other alternatives are successively tried

ID :1-5:acOff: 3Dest: e5

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Burst admission

e1

1

2

3

4

e55

ID :1-5:acOff: 3Dest: e5

9156425

200325

-+NextOffsetDestIn this case, choosing 3 will lead to burst loss :offset is insufficient (2-3-4-5 3 hops)

ID :1-5:acOff: 2Dest: e5

3 should thus be excluded even there is no other solutionCAC Mechanism :

We assume a threshold TCAC and a minimal number of feedbacks FCAC

If the success estimation E is < TCAC while the number of received feedback is ≥ FCAC next hop is excluded

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3. Alternative research ideas in optical networks

• All-Optical Network Coding– For protection purposes mainly

p1,m p2,m

p1,s

p1+2,s

p1,m p2,m

p1,s p2,s

p1+2,s

[10] E. D. Manley et al. “All Optical Network Coding”, Elsevier Journal of Optical Communications and Networking, Volume 2, Number 4, April 2010

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OBS MultiCast

• Combine (adaptive) deflection routing with Multicast routing?

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Ad-hoc wireless optical networks

• Light beams can also propagate in the air (free space optics)– At relatively high speed on short distances

• Typically 10-40 Gbit/s < 200m• 1-10 Gbit/s < 10km

• Now they have to be manually installed• They might be automated in the future

– Beam tracking

– Ad-hoc topology organisation

• Major problem : almost ON/OFF – Obstacle : OFF

– Not as in Wifi, where obstacle only affect SNR

– Multicast protection required

Image source : http://www.systemsupportsolutions.com/

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Comments or questions ?

Thank you for your attention