Optically Switched Networking - PowerPoint PPT Presentation

About This Presentation
Title:

Optically Switched Networking

Description:

Part 1 Technology overview. Optical fibre as a connection medium ... Device interconnects, Cluster/supercomputer interconnects, Storage Area Networks, ... – PowerPoint PPT presentation

Number of Views:81
Avg rating:3.0/5.0
Slides: 32
Provided by: michael1654
Category:

less

Transcript and Presenter's Notes

Title: Optically Switched Networking


1
Optically Switched Networking
  • Michael Dales
  • Intel Research Cambridge

2
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

3
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

4
Part 1 Technology overview
5
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

6
Optical fibre links
  • Not all good some problems
  • Polarisation sensitivity
  • Chromatic dispersion
  • Non-linear behaviour
  • Fibre more delicate
  • Cant be thrown around like copper
  • Minimum coil radius
  • Coupling/splitting costs

7
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

8
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

9
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(?)

10
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

11
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

12
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

13
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

14
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

15
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 youll get through

16
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

17
Part II - Example
18
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

19
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

20
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

21
Overview
22
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

23
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

24
Switch fabric
  • Demonstrated switching 10 10 Gbps channels
    through an SOA

55us/div Packet is 94.72us data, 1.28 us guard
band
25
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

26
Wavelength striping
From arbiter grant
To arbiter Request
Incoming packet
To optical switch
27
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

28
Testbed overview
  • Built a 3 node test-bed
  • Two main components host interfaces and switch
  • Control electronics on FPGAs
  • 2 data l in 1500nm range
  • 1 control l in 1300 nm range
  • Couplers/AWGs used to combine/split ls

29
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!

30
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

31
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
Write a Comment
User Comments (0)
About PowerShow.com