ARC Special Research Centre for Ultra-Broadband Information Networks Control of Optical Fibre Communications Networks Peter Farrell

Utopian Vision ALL OPTICAL NETWORK Analogy with Internet Transmitter sends photons through the network (transparently) to Receiver Format independent Bit-rate independent Protocol independent The Network is very clever (BRIGHT?) and can figure everything out so that your information goes to its destination perfectly A bit like –electricity too cheap to meter from the nuclear industry OR –the paper free office

Interesting Problems to Solve to build Utopia Finance All the routing problems in the Network BIG optical switches Control of adjustable elements in the Network

HOW BIG?

Worldwide?

Continental

Metro

Campus

Size matters because … Different transmission issues for –100 mbuilding / campus –1 kmcampus –10 kmmetro –100 kmmetro/continental –1000 kmcontinental –10000 kmworld All optical network requires (?) km infrastructure for a 100 m connection

Optical Network Control Most published work is on making connections, fault location, contention avoidance and so on Very little on control of adjustable elements in the network to optimise or at least improve the performance Alternative is to grossly over engineer the hardware

Point to Point Link Impairments Tx –Chirp –Noise –Finite extinction ratio Mux/Demux –Filter drift –Crosstalk Transmission fibre –Loss –Dispersion –Nonlinear effects Amplifiers –ASE/ Noise –Crosstalk –Wavelength dependent gain Rx –Finite sensitivity –Noise –Bandwidth Everywhere –PMD Tx Rx DisCo

Point to Point Link Adjustments Tx –Power, wavelength, chirp, modulation format, extinction ratio MUX/DEMUX –Temperature Amplifier –Gain, gain flattening filter, tilt Dispersion compensation Rx –Gain (APD or preamp gain) –Decision Threshold –Decision Point Tx Rx DisCo

C Blue C Red Tx Rx L Blue L Red L Blue L Red Rx Tx Terminal Amp n Amp1 Rx Terminal Tx … Transmission Fibre DCF C Blue C Red CCC LMLM DCF R LF CCC LMLM DCF R LF LMLM DCF LF DCF R LF CC C Long Haul Link Configuration 10 Gbit/s over >1000 km

Point to Point Link with OADM Tx Rx DisCo Tx Rx DisCo OADMOADM

OADM X

All Optical Network Tx Rx Tx

Lots of Feedback Loops …Amplifier Issues –Measurement accuracy –Signal reduction –Transient response Feedback & Control

Lots of Feedback Loops … Dispersion Compensator Issues –Location –Accuracy –Signal reduction Dispersion Compensator Dispersion Measurement

Lots of Feedback Loops … Pre-emphasis Shares OSNR, BER or received power equally among channels by adjusting transmit power with time varying disturbances Simple linear iterative algorithm (and variations on this theme) (Chraplyvy et al 1992) Non-linear channel!!!! Like to know –if non-linearity is significantly affecting performance –Origin of non-linearity

Feedback Loops What do we measure and where? –BER –Channel Powers –OSNR –Dispersion –Non-linearity –Crosstalk Local? Central? Tradeoffs between non linearity, dispersion and gain How many channels? Circuit switched or Packet switched? Interaction with routing algorithms

Control.. THE WHOLE NETWORK – WORLD DOMINATION Link by Link Device by Device

All Optical Network Tx Rx Tx

Point to Point Link Impairments Tx –Chirp –Noise –Finite extinction ratio Mux/Demux –Filter drift –Crosstalk Transmission fibre –Loss –Dispersion –Nonlinear effects Amplifiers –ASE/ Noise –Crosstalk –Wavelength dependent gain Rx –Finite sensitivity –Noise –Bandwidth Everywhere –PMD Tx Rx DisCo

Point to Point Link Adjustments Tx –Power, wavelength, chirp, modulation format, extinction ratio MUX/DEMUX –Temperature Amplifier –Gain, gain flattening filter, tilt Dispersion compensation Rx –Gain (APD or preamp gain) –Decision Threshold –Decision Point Tx Rx DisCo

Conclusion Model network Use standard control theory to construct a controller