Transcript Document

TCOM
Optical Networking:
Principles, Hot Topics
and Future Perspectives
November 24
Sébastien Rumley
EPFL – Laboratoire de Telecommunication (TCOM)
[email protected]
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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
Technological research
Academic research
• 3. Alternative ideas
– All Optical Network Coding
– OBS multicast
– Ad-hoc wireless optical networks
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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
Bending losses
Absorption/Scattering
Laser + modulation
Input data
•
Photodiode
Fibre (wave guide)
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) !
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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
This profile is different for each fibre
2. Modulation speeds
–
–
In theory, bandwidth of ~2x20 Thz
 ~80 TBaud/s (Nyquist)
Not realisable in practice
3. Impairments:
–
–
Non linear effects
Chromatic dispersion
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Image source : http://www.fiberoptics4sale.com/wordpress/optical-fiber-attenuation/
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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 :
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http://www.imec.be/ScientificReport/SR2008/HTML/1225202.html
http://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 amplification
Demodulate 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 amplification
Similar 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
:
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http://www.fiberopticsonline.com/article.mvc/Alcatels-new-OXC-leverages-bubble-technology-0001 9/37
https://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)
Not in the scope of this talk
• 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
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Optical networks – goals and challenges
GOALS :
• Above all: deliver bits
–
–
–
–
•
High throughput
High availability
Low congestions
No errors
– Reduce the cascaded
overprovisionning
– Minimize the frequency « trap »
•
Minimize the risks
– Network must be under control
– Capacity must be available
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Reduce energy consumption
– Avoid per bit operations
– Rationalise the utilisation
Minimize the costs
– Energy
– Investments
– Maintenance
•
CHALLENGES :
• Improve network 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:
–
•
•
•
To find:
–
Network capacities
a route and a wavelength for each lightpath
a matrix of demands
A list of capacities (fibres and λ)
a route and a wavelength for each lightpath
Constraints:
–
–
•
–
–
a matrix of demands (# lightpaths required
between each source-destination pair)
To find:
–
–
Network planning version
• Given:
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
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•
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.PA1
Skorin-Kapov, “Routing and wavelength assignment in optical networks using bin packing based algorithms
Rev
[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.PA1
Marsden, A. Maruta, K.-I. Kitayama, “Routing and Wavelength Assignment Encompassing FWM in
Rev
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
b
– They should be placed only in strategic places
a
c
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
e
d
g
f
a-c-b
CL=1
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
CL=2
In this example, two solutions to reduce CL:
CL=3
A) Add a regenerator in d
B) Reroute e-f-d-g  e-a-c-g
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f-d-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
a
10
b
10
S
d
10
8
8
8
8
c
b
10
S
x
8
8
a
10
10
8
8
c
e
(a)
x
d
e
(b)
• Minimize the sites  oblige lightpath to take detours
 More regenerations and more routing costs
5
a
5
5
x
d
a
8
5
d
x
8
10
8
S
5
b
10
y
8
5
5
z
c
Regenerations :
Routing cost : 3x(8+5+5) =
3
54
(b)
Regenerations :
Routing cost : 2x(8+5+10) + 18 =
5
64
5
e
y
10
5
f
(a)
5
b
S
8
10
c
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8
5
e
(a)
5
f
z
(b)
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Multi-objective optimisation
CP-RegRoutingSites
CP-RegSitesRouting
CP-Sites
30
40
CP-SitesRegRouting
(in %)
penalty(in
Routing
C1 penalty
Enum-Sites
15
10
30
20
10
5
0
0
0
25
0.25
0.5
0.75
0
0.25
40
Relative optical reach
)
20
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)
30 nodes
20
C2 penalty (in %)
CP-SitesRoutingReg
Enum-RegSites
25
30
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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.PA1
Qiao, M. Yoo, “Optical Burst switching (OBS) – a new paradigm for an optical internet, Journal of high
Rev
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
– Estimated setup
- Explicit release
- 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
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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
Buffering with FDL
Flow smoothing and synchronisation
Burst deflection
Redimensioning
Not viable economically
Traffic engineering – load balancing
Adaptive load balancing
Connection Access Control (CAC)
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Our goal
Integrate in one single scheme :
A burst deflection
An adaptive load balancing
A Connection Access Control (CAC)
Adaptive burst Admission and Forwarding
 perform this scheme directly at the OBS layer
[9] S. Rumley,
O. Pedrola, et al. “Feedback Based Load Balancing, Deflection Routing and Admission
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Control in OBS Networks”, Journal of Networks, Academy Publisher, Nov 2010
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In more details
ID :1-5:ac
e1
ID :1-5:ac
1,3
3
ID :1-5:ac
1
1
e5
ID :1-5:ac
1,3,4
4
5
1-5:ac OK
2
- Burst Control Packet (BCP) carries an ID
- BCP contains a list of visited nodes
- When a BCP is dropped…
… or arrives at destination
a feedback is sent to each node of the list
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Pending table node 1
In more details
ID :1-5:ac
Off: 4
Dest: e5
Dest
Offset
Next hop
1-5:ac
5
3
3
ID :1-5:ac
Off: 2
3
Dest: e5
ID :1-5:ac
Off: 3
Dest: e5
e1
ID
ID :1-5:ac
Off: 1
Dest: e5
Next1 : 3 !
ID :1-5:ac
Off: 0
Dest: e5
e5
5
1-5:ac OK
4
2
Dest
Offset
Next
+
-
2
1
2
0
0
…
…
…
…
…
5
3
3
0
1
0
…
…
…
…
…
- 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
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Burst forwarding
ID :1-5:ac
Off: 4
Dest: e5
ID :1-5:ac
Off: 3
Dest: e5
e1
3
e5
5
1
4
2
Dest
Offset
Next
+
-
5
3
2
134
5
96.4 %
5
3
3
241
6
97.6 %
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- 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
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Burst admission
ID :1-5:ac
Off: 3
Dest: e5
e1
1
3
e5
5
ID :1-5:ac
Off: 2
Dest: e5
4
2
Dest
Offset
Next
+
-
5
2
3
0
20
5
2
4
156
9
In this case, choosing 3 will lead to burst loss :
offset is insufficient (2-3-4-5  3 hops)
3 should thus be excluded even there is no other
solution
CAC 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
p1,s
– For protection purposes mainly
p1+2,s
p1,m
p2,s
p1,s
p1+2,s
p2,m
p1,m
[10] E. D.Rev
Manley
et al. “All Optical Network Coding”, Elsevier Journal of Optical Communications and Networking,
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Volume 2, Number 4, April 2010
p2,m
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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 :
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http://www.systemsupportsolutions.com/
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Comments or questions ?
Thank you for your attention
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