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8/9/2019 Towards Broadband Global Optical and Wireless Networking
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Towards Broadband GlobalTowards Broadband Global
Optical and Wireless NetworkingOptical and Wireless Networking
Marian Marciniak
National Institute of Telecommunications
Warsaw, Poland
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Acknowledgements toAcknowledgements to COST 266Advanced Infrastructure for Photonic Networks
COST 270Reliability of Optical Components and Devices in
Communications Systems and Networks
COST 273 Towards Broadband Mobile Multimedia Networks
URSI Commission DElectronics and Photonics
ITU Study Group 15 Optical and Other Transport Networks
IEC Technical Committee 86Fibre Optics andNEXWAY 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 theaccess 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@60GHz! light in fibres
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OUTLINEOUTLINE
y Introduction
Voice vs. IP specifics
y Transparent photonic transport network
y All - optical solutions
y Hybrid network concept
y Conclusions
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INTRODUCTIONINTRODUCTIONy Dramatic growth of Internet traffic.
y almost stable voice traffic .
y Actual networks are based on classical circuit
switching principle.y Internet and data traffic exhibit inherent packet
switched features.
Transparent terabit optical network infrastructure
provides 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
- - - - - optics
________ electronics
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EDFAEDFA The introduction ofErbium-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 beenused in order to cope with signal distortion.
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THENOTIONOFTHENOTIONOFTRANSPARENCYTRANSPARENCY
OFATRANSMISSIONLINK:OFATRANSMISSIONLINK:y the output signal is proportional to the signal at the
input.
This provides a potential to modulate and detect theoptical 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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Idealcase:Idealcase: 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, andoptical nonlinearities.
Real fibres PMD!
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Vacuum is the onlymedium
ideallytransparent:y no attenuation,
y no dispersion,
y and no nonlinear interactions.
Even in free-space optical beams are subjects of diffraction!
y diffraction is overcome in fibre based 1-D telecommunication links.
y It is compensated with the guiding core focusing properties,
Fibre modes are special beams having unique property of perfectlyvanished total effect of diffraction and focusing interplay.
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Transparent photonicTransparent photonic
networknetworky insures the scalability, i.e. possibility of future upgrades
y Almost unlimited capacity is available
New demands, especially in optical signal digital processing
y full 3R (4R?) regeneration (4th in spectral domain, Thyln, ICTON'99)
y Wavelength - new degree of freedom (wavelength-switched and routed
networks)y wavelength converters (PC)
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Transparencyof the network inTransparencyof the network in
practicalpoint of viewpracticalpoint of view::
The networks provides a telecommunication cloud
Clients send and receive properly their information
regardless of:
y Wavelength
y Transmission speed
y 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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Transparencyof:Transparencyof:
The fibre itself (attenuation spectrum)
The optical amplifier (gain spectrum)
Other system components.
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(lack of) Transparencyconstraints(lack of) Transparencyconstraints Ideal glass fibre
y attenuation
y chromatic dispersion
y nonlinear interactions
Real fibre: Polarization Mode Dispersion, PMD, results from randomlocal lack of circular symmetry of the fibre due to :
y technology imperfections
y local stresses caused by cable layout.
Those analogue features of a fibre result in:
y distortion,crosstalk
y and noise of the transmitted optical signal.
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The term "PMD" is usedThe term "PMD" is usedy in the general sense of two polarization modes having
different group velocities,
y and in the specific sense of the expected value of
differential group delay between two orthogonally
polarized modes.
y PMD causes the spreading of a pulse in the time domain
y It is actually the main transmission distance-limiting
factor in 40 Gbit/s systems and above
y as such it became recently a subject of intense research
both for fibre optimisation and characterization
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TransparencyconstraintsIITransparencyconstraintsII
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:
WDMorOTDM?WDMorOTDM?WDMorOTDM?
WDM channel spacing 100 GHz = 0.8 nm? 10 Gbit/s TDM ?
50 GHz ? 40 Gbit/s ETDM?
25 GHz ? 160 Gbit/s OTDM?
Requires 200 GHz WDM
12.5 GHz ? (y.2002 standard)
in future: 6.25 GHz? or 5 GHz?
400 Gbit/s OTDM?
What about 20 nm? Coarse WDM
Bandwidth limitations DWDM vs. OTDM trade-off
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The opticalsignalis characterisedbyThe opticalsignalis characterisedby
y temporal characteristics: shape absolute and relative(instantaneous power), and
y 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?
y To compensate for attenuation, optical amplifiers and especially
Erbium-Doped Fibre Amplifiers are already a well-developed
solution.
y To compensate for chromatic dispersion, dispersion-
compensating modules are developed with dispersioncompensating fibres and fibre gratings as typical examples.
y Unfortunately, it is especially difficult to compensate for
nonlinear distortion and interactions.
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Network behavesNetwork behaves
transparent way:transparent way:y we allow attenuation and / oramplification,
y and eventually wavelength conversion.
Transparent wavelength conversion assumes the
conservation of temporal signal shape, which is
superimposed to a different wavelength.
This works with wirelessmobile signal modulation of
the optical wave as well.
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Back to theAnalogueAgeBack to theAnalogueAge 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.
y The transparent length is a distance over which the signal
can be transmitted successfully.
y Transmission over longer lengths requires some form of
regeneration.
y The transparent length can increase in the future, when thetechnology is sufficiently developed.
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Opticalswitching in adynamicOpticalswitching in adynamic
WDMnetworkenvironmentWDMnetworkenvironment
Instantaneous network parameters are
y bit-rate
y WDM channel powery Aggregate optical power
y Number of WDM channels
y Wavelengths
y Transmitter and amplifier output power and
y nonlinear interaction resulting from
y attenuation, chromatic dispersion and PMD
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The "history" of thesignalThe "history" of thesignal
i.e. How much it has suffered from analogue distortion,
noise, cross-talk etc.
History may be differentfor different WDM channels
History may vary
in a dynamic wavelength allocation environment
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Degrees of freedom
of an optical network
space3- space
time ( DM )
avelengt (WDM)
v2 polarisatio s!
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Optical switching & routingOptical switching & routing
Degrees of freedom of an optical network:
y 3-D space co-ordinates,
y time (and resulting possibility of Optical Time Domain
Multiplexing, OTDM),
y wavelength (WDM),y polarisation
Opportunities for optical switching:
y in space, temporal, wavelength, and polarisation domains.
In addition to that,
logical on/offswitching is performed in optical logic elements.
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Optical routingOptical routing
can be realised as wavelength routing in a transparent
way.
y an analogue and passive solution,
y or an analogue and active one if wavelength
conversion is applied.
All-optical packet routing
y involves some intelligence of the router
y and some decision based on the information included
in the packet.
not realisable transparent way !
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BASICFACTS
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 forall-optical switching/signal processing !
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AllAll--Optical OpacityOptical 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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HYBRIDNETWORKCONCEPT
oice and broadband wireless signals transmitted via
circuit-switched subnetworkwith digital (voice) or
analogue (wireless) coding,
while IP is transmitted as packet-switchedconnectionless 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 + IPhybrid network table
Characteristics Voice, real-time
incl. Mobile wireless signal
Internet, data
Basic principle Circuit-switched /ATM Packet-switched
Packet length Constant length cells Variable
Lost data No retransmission Retransmitted
Quality of Service Guaranteed by overprovisioning Best-effort
Traffic Deterministic Statistic
Other Instantaneous bandwidth (# of s)
controlled logically in IP routers
Intelligence
Transparent Includes all-optical opacity
Bandwidth Dedicated on demand As wide as available
Access Conventional twisted-pair access to
public exchange offices for voice,
or wireless access
Broadband access to servers,
e.g. via cable-TV
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CONCLUSIONSCONCLUSIONSHybrid network saves voice technology with transparent transmission.
Real-time traffic including mobile wireless realised via dynamicallyallocated 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?