Optically Switched Networking
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Transcript Optically Switched Networking
Optically Switched
Networking
Michael Dales
Intel Research Cambridge
www.intel.com/research
• Intel Research •
Overview
Part 1 – Technology overview
Optical fibre as a connection medium
Optical switching fabrics
Optical switches
Part 2 – Example network
SWIFT Architecture overview
Current work
Research topics
www.intel.com/research
• Intel Research •
Recommended reading
If optical networks turn you on then the following text
book is worth seeking:
“Optical Networks, A Practical Perspective” by Rajiv
Ramaswami and Kumar N. Sivarajan, Morgan Kaufman
www.intel.com/research
Part 1 – Technology
overview
www.intel.com/research
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Optical fibre links
Optical fibre – yet another wire
Advantages:
Capacity – long haul links of 160 Gbps over a single fibre
Range – signal can travel further without regeneration
Noise immunity – does not suffer from EM interference
Weight/space – a lot lighter/smaller than copper
Power – …
Popular in the long haul network
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Optical fibre links
Not all good – some problems:
Polarisation sensitivity
Chromatic dispersion
Non-linear behaviour
Fibre more delicate
Can’t be thrown around like copper
Minimum coil radius
Coupling/splitting costs
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Optical fibre links
In copper we use TDM to multiplex multiple
channels on a single link
In fibre can also use Wavelength Division
Multiplexing (WDM)
Each wavelength (lambda, l) can carry a different
channel
Free extra wires!
Can TDM each wavelength too
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Switched optical networks
Optical links are common in high speed switched networks:
ATM, Infiniband, Fibre-channel
But all these networks convert data back to electrons at the
switch
PD
PD
PD
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Switched optical networks
O-E-O switch design makes it easy to design an
optical network (just like copper ones!)
Disadvantages:
Size/power – need to duplicate electronics for each
lambda
Latency – O-E-O conversion takes time
Bandwidth – for really high capacity, electronics can
become the bottleneck(?)
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Optically switched networks
A key focus of the optical network community is to
find ways to make all optical networks
Packets stay in photons from edge to edge
Techniques used depend on traffic type – circuit
switching and packet switching have very different
requirements
Might want to move to different wavelength across
switch
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Optical switch fabrics
Switch fabric design covered later in course
Here we look at switching elements for light
Need a way to switch light from one port to another
Many possible ways with varying loss, switching time,
polarisation dependency, etc.
Mechanical – moveable mirrors
Can uses MEMS devices for compactness (e.g., glimmerglass)
Thermo-optical – heat it to change
Electro-optical – control by current
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Buffering?
In an electronic switch we use buffering to:
Delay packet whilst we decide what to do with it
Resolve contention when multiple packets want to go to
the same place at the same time
There is no optical equivalent of random access
memory
Best we have are Fibre Delay Lines
Use a long loop of fibre to delay the signal for a while
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• Intel Research •
Optical switches
The switching fabric is only half the story – how do
we decide where to switch the packet?
In electronic switch read header and then route
through fabric accordingly
In optical switches we have three options:
Convert the header to electrons and process electronically
Process the header optically using optical logic
Forget it all and use some form of reservation
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Optical switches
Use electronics to route packet:
Read header from photons and convert to electrons
Use a FDL to buffer packet whilst switch makes decision
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Optical switches
Alternatively use reservation – signal ahead of time
that a packet is coming, typically on a reserved l
One popular technique is Optical Burst Switching
Packets grouped into a burst at source to amortise
overhead
Control packet fired into network ahead of time – passes
through switches setting up a path
A fixed-delay time later the burst is sent through network
No guarantee that you’ll get through
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Optical switches
Alternatively use photonic devices to perform optical
header reading
No need to convert to electrons
Still not a prime time technology – can only handle a
couple of addressing bits
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Part II - Example
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SWIFT optical network
SWIFT is a research project between Intel
Research, University of Cambridge, Essex
University, and Intense Photonics
Aim to built a short range, high capacity, wavelength
striped, optically switched, packet switched network
Aim for 100 Gbps and up
Use photonic devices under electronic control
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SWIFT motivation
Optics traditionally used in long haul, but not in short
range, where copper dominates…
…but copper will eventually run out (eventually…)
SWIFT looks at applying optics to short range:
Device interconnects, Cluster/supercomputer
interconnects, Storage Area Networks, etc.
Want have optical data-path, but still use electronics
for control
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Architecture overview
A short range packet switched network based upon:
WDM to increase bandwidth per link
An all optical data path
A single switch for simplicity (for now)
An electronic control plane
Use WDM for l striping – use all ls for one channel
Create a light bus
Reserve one channel for control
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Overview
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Switch design
Optical data-path: packets remain optical
throughout the network
Light-paths need to be constructed through the
switch before packets arrive
Asynchronous control signalling used to request
switch configuration
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Switch fabric
Many light switching technologies, ranging
from mechanical mirrors to semiconductor
solutions
Switch response time is important for packet
switching
We use Semiconductor Optical Amplifiers
(SOAs)
Turn light on or off based on an electrical input
Have a switching time of a few nanoseconds
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Switch fabric
Demonstrated
switching 10 * 10 Gbps
channels through an
SOA
55us/div – Packet is 94.72us data, 1.28 us guard band
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Host interface
Host interface has two main tasks
Taking packets and converting them to striped format
and vice versa
Negotiating with the switch for access
When a node wishes to transmit it requests
permission over the control channel and waits for a
light-path to be setup
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Wavelength striping
From arbiter grant
To arbiter Request
Incoming packet
To optical switch
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Demonstrator
Have built a test-bed network
Goal is to allow practical evaluation at many levels:
Photonics evaluation
MAC layer testing
Real application performance
Used to validate a simulation model for
investigation of network scaling
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Testbed overview
Built a 3 node test-bed
2 data l in 1500nm range
Two main components: host
interfaces and switch
1 control l in 1300 nm
range
Control electronics on FPGAs Couplers/AWGs used to
combine/split ls
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Current demonstrator
Current setup seen here
Three racks:
1: switch
2: host interface board
3: host interface transceivers
PCs off shot
Large due to using off the
shelf components!
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Status
Recently got first stage working
Switches packets between nodes
Data striped over both wavelengths
Can run TCP, UDP, ICMP, etc. end to end
Currently tuning performance for benchmarking
Have simulation model in NS2 ready to correlate
against testbed
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Future work
Looking at several areas, including
Switch fabric design
Photonic device control
Current SOA configuration done manually
Want to automate this process using electronics
Network scheduling and management
Improve on request/grant protocol
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