Towards Broadband Global Optical and Wireless Networking

1
Towards Broadband Global Optical and Wireless
Networking Marian Marciniak National Institute
of Telecommunications Warsaw, Poland
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Acknowledgements to

• COST 266 Advanced Infrastructure for Photonic
  Networks
•  
• COST 270 Reliability of Optical Components and
  Devices in Communications Systems and Networks
• COST 273 Towards Broadband Mobile Multimedia
  Networks
•  
• URSI Commission D Electronics and Photonics
•  
• ITU Study Group 15 Optical and Other Transport
  Networks
•  
• IEC Technical Committee 86 Fibre Optics
•  
• and NEXWAY Network of Excellence

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MOTIVATION

• Radio-over-fibre transmision can be realised in
  the core networks even at large distances, with
  potential of amplification/switching in the
  optical domain - COST Action 273 Towards
  Broadband Mobile Multimedia Networks
• Radio-over-fibre arrangements can be applied in
  the access part of the Mobile Broadband Systems
  (MBS) in 60 GHz band.
• The 60 GHz millimeter-wave band is a goal
  frequency band for mobile broadband services
  allocation.
• attenuation 10dB/km_at_60GHz! light in fibres
  lt0.2dB/km
• This study to propose a hybrid network for
  Global Optical and Wireless Networking

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OUTLINE

•      Introduction
• Voice vs. IP specifics
•      Transparent photonic transport network
•      All - optical solutions
•      Hybrid network concept
•      Conclusions
•  

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INTRODUCTION

•      Dramatic growth of Internet traffic.
•      almost stable voice traffic .
•      Actual networks are based on classical
  circuit switching principle.
•      Internet and data traffic exhibit inherent
  packet switched features.
• Transparent terabit optical network
  infrastructureprovides an excellent realization
  of circuit switched network.
• But it is not capable to realise packed switched
  services in an efficient way.

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Voice traffic

• Circuit switched
• Deterministic
• Real time, i.e. without noticeable delays
• no retransmission if some bits are lost
• inherent Quality of Service guarantees
• Well developed SDH/ATM technology

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Packet traffic

• Statistic (bursts!)
• Packet switched, connectionless
• best effort, no QoS guarantees
• Latency (time delay)
• lost packets, can be retransmitted
• efficient optical buffering wanted!

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Transparency story
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- - - - - optics ________ electronics
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EDFA

•  
• The introduction of Erbium-Doped Fibre Amplifiers
  (EDFA) which have replaced electronic
  regenerators in fibre based transmission links in
  early 90s resulted in optical transparency of the
  links.
• This was in contrary with electronic regenerator
  based links. In those a combination of electronic
  logic circuit along with electro-optical and
  opto-electrical conversions of the digital signal
  transmitted has been used in order to cope with
  signal distortion.

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THE NOTION OF TRANSPARENCY OF A TRANSMISSION
LINK

•      the output signal is proportional to the
  signal at the input.
• This provides a potential to modulate and detect
  the optical wave power with microwave or
  milimetre wave envelope
•  The transparency is rather an analogue feature
  of a link what is in contrary to digital
  transmission schemes.
•  Transparency in optical domain has its common
  sense
• a medium is transparent if the light goes
  through it.

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Ideal case

• signal at the output exactly the same as in the
  input,
• obviously with acceptation of time delay caused
  by finite value of light velocity,
• and eventually of attenuation of the signal
  power.
• But without degradation of its other
  characteristics!
•  Unfortunately that ideal situation is not
  realisable in an optical network.
• Even an ideal glass fibre exhibits
  attenuation,chromatic dispersion, and optical
  nonlinearities.
• Real fibres PMD!

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Vacuum is the only medium ideally transparent

•      no attenuation,
•      no dispersion,
•      and no nonlinear interactions.
•  
• Even in free-space optical beams are subjects of
  diffraction!
•      diffraction is overcome in fibre based 1-D
  telecommunication links.
•      It is compensated with the guiding core
  focusing properties,
• Fibre modes are special beams having unique
  property of perfectly vanished total effect of
  diffraction and focusing interplay.

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Transparent photonic network

•     insures the scalability, i.e. possibility of
  future upgrades
•     Almost unlimited capacity is available
• New demands, especially in optical signal digital
  processing
•     full 3R (4R?) regeneration (4th in spectral
  domain, Thylén, ICTON'99)
•     Wavelength - new degree of freedom
  (wavelength-switched and routed networks)
•     wavelength converters (?C)

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Transparency of the network in practical point of
view

•  
• The networks provides a telecommunication cloud
• Clients send and receive properly their
  information regardless of
•         Wavelength
•         Transmission speed
•         Format used (analogue, digital)
• Data need no special adaptation procedure to be
  transmitted through the network.
• Possibility to modulate optical wave with
  microwave signal

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Transparency of

•  
• The fibre itself (attenuation spectrum)
• The optical amplifier (gain spectrum)
• Other system components.

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(lack of) Transparency constraints

• Ideal glass fibre
•       attenuation
•       chromatic dispersion
•       nonlinear interactions
•  
• Real fibre Polarization Mode Dispersion, PMD,
  results from random local lack of circular
  symmetry of the fibre due to
•       technology imperfections
•       local stresses caused by cable layout.
•  
• Those analogue features of a fibre result in
•       distortion, crosstalk
•       and noise of the transmitted optical
  signal.

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The term "PMD" is used

•       in the general sense of two polarization
  modes having different group velocities,
•       and in the specific sense of the expected
  value of differential group delay lt?tgt between
  two orthogonally polarized modes.
•   
•       PMD causes the spreading of a pulse in the
  time domain
•       It is actually the main transmission
  distance-limiting factor in 40 Gbit/s systems and
  above
•       as such it became recently a subject of
  intense research both for fibre optimisation and
  characterization

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Transparency constraints II

•  
• Very high wavelength precision and stability of
  optical sources is a fundamental requirement of a
  Dense WDM network
•  
• This increases the cost of the devices.
•  
• Goal not to loose that precious wavelength !
•  
• Solution keeping the signal in the optical
  domain while it traverses as large part of the
  network as possible.
•  
• This is why transparency is a so important issue.

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Some questions WDM or OTDM?
Bandwidth limitations ? DWDM vs. OTDM trade-off
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The optical signal is characterised by

•      temporal characteristics shape absolute
  and relative (instantaneous power), and
•      spectral characteristics.
• So what we do in order the output signal
  resembles the input one as much as possible, or
  at least it is detectable properly?
•      To compensate for attenuation, optical
  amplifiers and especially Erbium-Doped Fibre
  Amplifiers are already a well-developed solution.
•      To compensate for chromatic dispersion,
  dispersion-compensating modules are developed
  with dispersion compensating fibres and fibre
  gratings as typical examples.
•      Unfortunately, it is especially difficult
  to compensate for nonlinear distortion and
  interactions.

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Network behaves transparent way

•  
•      we allow attenuation and / or
  amplification,
•  
•      and eventually wavelength conversion.
•  
• Transparent wavelength conversion assumes the
  conservation of temporal signal shape, which is
  superimposed to a different wavelength.
• This works with wireless mobile signal modulation
  of the optical wave as well.

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Back to the Analogue Age

• Transparent components of the optical network
  treat the passing signals in an analogue way.
• Broadband wireless is transmitted as an optical
  wave properly modulated in an analogue way.
•       The transparent length is a distance over
  which the signal can be transmitted successfully.
  
•       Transmission over longer lengths requires
  some form of regeneration.
•       The transparent length can increase in the
  future, when the technology is sufficiently
  developed.

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Optical switching in a dynamic WDM network
environment

• Instantaneous network parameters are
•           bit-rate
•           WDM channel power
•           Aggregate optical power
•           Number of WDM channels
•           Wavelengths
•           Transmitter and amplifier output power
  and
•           nonlinear interaction resulting from
•           attenuation, chromatic dispersion and
  PMD

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The "history" of the signal

•  i.e. How much it has suffered from analogue
  distortion, noise, cross-talk etc.
•  
• History may be different for different WDM
  channels
•  
• History may vary in a dynamic wavelength
  allocation environment

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Degrees of freedom of an optical network
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Optical switching routing

• Degrees of freedom of an optical network
•      3-D space co-ordinates,
•      time (and resulting possibility of Optical
  Time Domain Multiplexing, OTDM),
•      wavelength (WDM),
•      polarisation
• Opportunities for optical switching
•      in space, temporal, wavelength, and
  polarisation domains.
• In addition to that,
• logical on/off switching is performed in optical
  logic elements.

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Optical routing

• can be realised as wavelength routing in a
  transparent way.
•      an analogue and passive solution,
•      or an analogue and active one if wavelength
  conversion is applied.
• All-optical packet routing
•      involves some intelligence of the router
•      and some decision based on the information
  included in the packet.
•      not realisable transparent way !

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BASIC FACTS

• Two electrons interact via electromagnetics
• While two photons do not at all!
• This is
• Main cause of the great success of optical
  transmission
• but
• Means great difficulities for all-optical
  switching/signal processing !

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All-Optical Opacity

•  Even though all-optical routing element involves
  optical logics, optical memory, etc.,
• it is not optically transparent and it exploits
  optically opaque elements.
•  
• The signal remains in optical domain, but digital
  operations result in that the fundamental
  transparency condition of proportionality of
  output and input signals is not satisfied.

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HYBRID NETWORK CONCEPT

• Voice and broadband wireless signals transmitted
  via circuit-switched subnetwork with digital
  (voice) or analogue (wireless) coding,
• while IP is transmitted as packet-switched
  connectionless traffic.
• Voice/wireless is carried on dynamically
  allocated wavelengths, according to instantaneous
  demand for real-time services.
• The two kinds of traffic are separated and
  interleaved in frequency (wavelength) domain, not
  in time domain.

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Voice IP hybrid network table
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CONCLUSIONS

• Hybrid network saves voice technology with
  transparent transmission.
• Real-time traffic including mobile wireless
  realised via dynamically allocated wavelengths as
  circuit-switched traffic.
• The number of wavelengths allocated by IP layer
  for instantaneous demand for real-time traffic.
• Broadband wireless signal modulates the optical
  wavelength power.
• All remaining wavelengths are for the IP traffic.
  
• IP free of real-time restrictions, with potential
  of
• variable-packet length,
• no idle bits,
• best-effort scheme.
• Whole available bandwidth can be fully exploited.
  
• Quality of Service can be differentiated for IP.
• .

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Thank You

• Questions?