Lecture: 9 Elastic Optical Networks
Ajmal Muhammad, Robert Forchheimer
Information Coding Group
ISY Department
Outline


Motivation
Elastic Optical Networking



Flexible spectrum grid, tunable transceiver, flexible OXC
Flexible Optical Nodes
Routing and Spectrum Assignment Problem
Research Motivation
Emerging applications with a range of transport requirement
Future applications with unknown requirements
Flexible and efficient optical networks to support existing, emerging and
future applications
Courtesy: High performance network
lab., Bristol
Applications with Diverse Requirements
Media
High-speed data
400G, 1Tb/s
Courtesy: High performance network
lab., Bristol
Evolution of Transmission Capacity
Spectral Efficiency (SE) Improvement
Fixed optical amplifier bandwidth (~ 5 THz)

Per fiber capacity increase has been accomplished through boosting SE (bit
rate, wavelength, symbol per bit, state of polarization)
TDM
WDM
1
BPSK
QPSK
DP-16QAM
DP-64QAM
0.1
Multi-level mod.
PDM
Multiplexing technology evolution
0.01
0
10
DP-QPSK
0.1
DP-256QAM
@25 Gbaud
DP-1024QAM
0.01
100 200 300 400 500 600
Bit rate per channel (Gb/s)
Spectral efficiency (b/s/Hz)
Optical amplifier bandwidth (~ 5 THz)
Relative optical reach with
constant energy per bit
Bit loading higher than that for DP-QPSK causes rapid increase in
SNR penalty, and results in shorter optical reach
SE improvement is slowing down, meaning higher rate data need
more spectrum
Current Optical Networks :: Inflexible
Super-wavelength
Courtesy: High performance network
lab., Bristol
Current Solution for Bandwidth-Intensive
Applications
Optical virtual concatenation (OVC) for high capacity end-to-end
connection (super-wavelength)
Demultiplex the demand to smaller ones such as 100 or 40 Gb/s, which
can still fit in the fixed grid (Inverse multiplexing)
Several wavelengths are grouped and allocated end-to-end according
to the application bandwidth requirements
Grouping occurs at the client layer without really affecting the network
Connection over several wavelengths is not switched as a single entity
in network nodes
Elastic Optical Networking
The term elastic refers to three key properties:
The optical spectrum can be divided up flexibly
Courtesy: Ori Gerstel, IEEE Comm. Mag. 2012
Elastic Transceivers
The transceivers can generate elastic optical paths (EOPs); that is
path with variable bit rates
Tunable transceiver
Courtesy: Steven Gringeri, IEEE Comm. Mag. 2013
Flexible Switching
The optical nodes (cross-connect) need
to support a wide range of switching
(i.e., varying from sub-wavelength to
super-wavelength)
EONs
WDM Networks
Bandwidth Variable
Drivers for Developing the EONs
Support for 400 Gb/s, 1Tb/s and other high bit rate demands
Disparate bandwidth needs: properly size the spectrum for each
demand based on its bit rate & the transmission distance
Tighter channel spacing: freeing up spectrum for other demands
Reach vs. spectral efficiency trade-off: bandwidth variable transmitter
can adjust to a modulation format occupying less optical spectrum for
short EOP and still perform error-free due to the reduced impairments
Dynamic networking: the optical layer can now response directly to
variable bandwidth demands from the client layers
Elastic Optical Path Network:: Example
Path length
Bit rate
Conventional
design
1,000 km
400 Gb/s
Fixed
format, grid
QPSK
Elastic
optical path
network
Adaptive
modulation
Elastic channel
spacing
1,000 km
200 Gb/s
QPSK
200 Gb/s
1,000 km
100 Gb/s
QPSK
250 km
250 km
400 Gb/s
100 Gb/s
16QAM
16QAM
Outline


Motivation
Elastic Optical Networking



Flexible spectrum grid, tunable transceiver, flexible OXC
Flexible Optical Nodes
Routing and Spectrum Assignment Problem
Common Building Blocks for Flexible OXCs
Reconfigurable Optical Add-Drop
Multiplexer (ROADM)
Optical splitter
Add channels
Wavelength
selective switch
Drop channels
Multi-Granular Optical Switching
FXC: Fiber switch
BTF: Band to Fiber
BXC: Waveband switch
WXC: Wavelength switch
Add channels
Drop channels
Architecture on Demand (AoD)
Courtesy: High performance network
lab., Bristol
MEMS switch is used to interconnected all the
Input-output ports and switching devices
Optical backplane cross-connections for AoD OXCs
AoD Node
Aimed to develop an optical node that can adapt its architecture
according to the traffic profile and support elastic allocation of resources
Flexible OXC Configuration
Backplane implemented with 96x96 3D-MEMS
Flexibility to implement and test several switch architectures on-the-fly
Switching time 20ms
Courtesy: High performance network
lab., Bristol
Outline


Motivation
Elastic Optical Networking



Flexible spectrum grid, tunable transceiver, flexible OXC
Flexible Optical Nodes
Routing and Spectrum Assignment Problem
Routing and Spectrum Assignment (RSA)
Spectrum variable (non-constant)
connections, in contrast to standard
WDM
Planning Elastic/Flexgrid Networks
Input: Network topology, traffic matrix, physical layer models
Output: Routes and spectrum allocation RSA
(RMLSA include also the modulation-level used – 2 flexibility degree:
modulation and spectrum)

Minimize utilized spectrum and/or number of transponders, and/or…

Satisfy physical layer constraints

0
1

0

1
2

0
1 2 1 0 1
0 1 1 0 1 
1 0 1 1 1

0 1 0 2 0
1 0 1 0 1

2 1 1 1 0
23
Examples
RMLSA
RSA
Courtesy: Ori Gerstel,
IEEE Comm. Mag. 2012
Cost-Efficient Elastic Networks
Planning Using AoD Nodes
Conventional ROADMs
AoD ROADMs