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Access Networks

lectures 2008/09- winter termPart 3: Classification of Access Networks

3.3 Optical Access Networks (OAN)

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OAN =

- access system with optical fibres and others optical and optoelectrical (optoelectronic) components + transmission of opt. signal through free space (opt. relay link)

- FITL (Fibre in the Loop)

- advantages: frequency broadband, high bit rate, ability to operate in large access area

-Phys. architecture:

- Logical arch.: Tree Fig.3.3.1

star

tree (multiple star)

bus

ring

OLT-optical line terminationONU – optical network unit

coupler

star coupler

1xN coupler

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The main parts of OAN – OAN architecture:ODN = Optical Distribution Network

NT = Network Terminal

ONU = Optical Network Unit – in the user end – local loop connection (sometimes also NTU)

Fig.3.3.2 Functional architecture of OAN

OLT = Optical Line Termination – in the exchange end – connection to the exchange

NTONU

ONU

ODN OLT

OAN

upstream

downstream

user sidenetwork side

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Architectures (variants) of FITL: pure optical (FTTT) + hybrid (optics + metallic lines - the others apart from FTTT):

FTTT (Fibre to the Terminal)

FTTP (...Premise)

FTTH (... Home)

FTTB (... Building)

FTTC (.... Curb – the edge of the footpath)

FTTE (... Exchange)

FTTO (...Office)

FTTCab (...Cabinet)

- on the metalic part (original POTS) there mostly operates VDSL system

Fig.3.3.3

Exchange

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-sometimes the most common solution – however, it is not OAN in fact

- opt. cable ends in central office, where is DSLAM, and from it the the connections go out.

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FTTO and FTTH are signified as fair optical – because the opt. fibers are led as far as famale plug (user socket).

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source: http://access.feld.cvut.cz/view.php?nazevclanku=&cisloclanku=2006051702

shared

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Fig.3.3.4: Reference configuration of OAN

Fig.3.3.5 Reference model of AN in the building

STB-SetTopBox

CPN-Customer Premises Network

B...Broadband

NB...Narrow Band

NTE-Network Termination Equipment

frequency splitters

Management of access network

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Reference configuration of OAN – continue: functional blocks OLT and ONU:

• system core

• functions of access to services

• common functions

Fig.3.3.6. OLT

Fig.3.3.7 ONU

Legend:

DCCF…

TMF…

ODNIF…

TUIF…

SPF…

OAMF…

CaSMF…

SIF…

PSF…

Switching network

Optical distr.network

Optical distr.network

User ports

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DCCF – Digital CrossConnect Function

TMF – Transport & Multiplexing Function

ODNIF – Opt. Distrib.Network Interface Function

TUIF – Tributary UNIT Interface Function

SPF – Signalling Processing Function

common functions

- OAMF – operation, administration and maintenance Function

- PSF - power supply function

C&SMF – Customer and Service Multiplex Functions

SIF – Service Interface Function

commutation and multiplex

- EOC function

- V5 interface

- conversion from signalling of switching system to signalling in AN

-control functions with access to overall network management TMN, and power supply

- demultiplexing

- services streams distribution

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ODN – Optical Distribution Network

-active one (AON – active optical network) - equipment with power supply

-passive one (PON = passive optical network) – only passive equipments; in the building; short distances

Fig.3.3.8 ODN classification according to DP (Distribution Point) properties

active DP passive DP

with EOC without EOC

several optical segments

unique optical segment

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PON technologyAPON – transport based on ATM cells (ITU-T G.983 standard )

BPON – Broadband PON – symetr.transports on higher bit rates (622,04 Mbps; either 2 vlákna, i.e. for each rout (direction) 1, or unique fiber with WDM

EPON – with Ethernet (Ethernet in the first Mile)

GPON – gigabit version PON, 1,244 a 2,488 Gbps (ITU-T G.984)

CWDM – Coarse WDM (coarse wave multiplexing) – interstage between WDM and DWDM (Dense WDM) – for the sake of cheaper increasing of information capacity, up to 8 channels, 1550nm window, uncooled lasers

hybrid -

Fig.3.3.9 Optical access equipment classification

Optical hardware

Point-to-Point (P2P)Multipoint (PMP)networks OAN

fibersrelay links -FSO

passive - PONactive - AON

TDM FDM CWDM

APON GPON EPON

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StandardsITU-T G.983

APON (ATM Passive Optical Network)-the first Passive optical network standard - primarily for business applications, and was based on ATM.

BPON (Broadband PON) - standard based on APON. It adds support for WDM, dynamic and higher upstream bandwidth allocation, and survivability. It also created a standard

management interface, called OMCI, between the OLT and ONU/ONT, enabling mixed-vendor networks.

ITU-T G.984 GPON (Gigabit PON) - an evolution of the BPON standard - supports higher rates, enhanced security, and choice of Layer 2 protocol (ATM, GEM, Ethernet). In early 2008, Verizon began

installing GPON equipment, having installed over 800 thousand lines by mid year. British Telecom, and AT&T are in advanced trials.

IEEE 802.3ah EPON or GEPON (Ethernet PON) is an IEEE/EFM standard for using Ethernet for packet data

-is now part of the IEEE 802.3 standard. IEEE 802.3av

10G-EPON (10 Gigabit Ethernet PON) is an IEEE Task Force for 10Gbit/s backwards compatible with 802.3ah EPON. 10GigEPON will use separate wavelengths for 10G and 1G downstream. 802.3av will continue to use a single wavelength for both 10G and 1G upstream with ATDMA separation. It will also be WDM-PON compatible (depending on the definition of

WDM-PON). It is capable of using multiple wavelengths in both directions. SCTE IPS910

RFoG (RFoverGlass) is an SCTE Interface Practices Subcomittee standard in development for Point to Multipoint (P2MP) operations that MAY have a wavelength plan compatible with data

PON solutions such as EPON,GEPON or 10GigEPON. RFoG offers an FTTH PON like architecture for MSOs without having to select or deploy a PON technology.

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Passive and active components of OAN

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Optical fibers and their properties

- max. modulation frequence band (bandwidth)

cladding

core

- velocity of light propagation ~ 2/3 of c (in vacuum)

- attenuation = {10log(P1/P2) } / length [dB/km]

- number of modes: 1-mode fibers and multimodes f. (larger Φ, the more number of modes), multimodes with step change of i, or with gradient change

- dispersion - (different velocity depending on λ, also different i limiting of λ band of fiber)

[1]

- on the base of Si-glass or plastic

Fig.3.3.10: Opt.fiber with both higher and lower order mode

Fig.3.3.11

i – diffraction index

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[5]

Fig.3.3.13 ...total reflection on the boundary line of fibre-cladding (coating)

...from optoelectronics:

boundary

100% reflection

18source: http://en.wikipedia.org/wiki/Image:Optical_fiber_types.svg

Fig. Optical fibers types

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n (or i) – diffraction index, v – velocity of propagation in solid material:

.fn

cv rrn

f

kv

-the most simple e-m waves – sinus: E(x,t) = E0cos(ωt-kx+Φ) – also: plane wave propagating in the direction x.

k=2π/λ .... wave number, Φ .... phase constante (start phase)

- remember also: - phase velocity

-the group of waves with closed λ – they are moving by ‘group velocity’:

kvg

- other terms: critical impact angle, totale reflection, law of reflection

...from optics / physics:

20[1]

optical fibers ...

Fig.3.3.15 Attenuation dependance on wavelength and other factors

The other properties of optical fibers:

reason of attenuation: presence and generation of OH ions, Raileigh scatter („total“ border, edge)

wave length

3rd window width2nd window

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Tab.3.3.1 Standard properties of 1-mode fiber by G.652

Wave length [nm] Max.chromatic dispersion [ps/(nm.km)]

Min./max. attenuation [dB/km]

1285-1330 3.5 0.3 – 1.0

1270-1340 6 0.3 – 1.0

1550 20 0.15 – 0.5

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POFs = Plastic Optical Fibres

- traditionally PMMA (acrylic) or new perfluorinated polymer core in fluorinated polymer cladding

- equivalent to multimode glass fibers - plastic core (Φ about 1 mm) with step index profile

- cheaper, suitable for LAN – for data and signals transport – in FTTH technology

- manipulation with them is more simple

- their specific attenuation is higher then this one of glass fibers; but they are in development (!)

- good properties in unfriendly conditions (near the high voltage transformer stations) – that means they are resistant to disturbance, they are elastic (flexible)

- EoPOF – Ethernet over POF

info – e.g.: http://en.wikipedia.org/wiki/Plastic_optical_fiber

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Other passive components of OAN:

Couplers – basic is so called “Y“ or “1 x 2“.

2 x 2 - devides signal from A to C andD but, there is possible also transmission of light into all 8 directions

Creation of couplers – by fusion or by „tapering“

[1], [5]Fig.3.3.16 -a,b,c,d

-or splitters

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Transmission Star Coupler Reflection star coupler

[1]

Fig..3.3.17 - a,b,c

- the light arrives for instance at port A and is split equally through ports from G to L.

-the light arrives for instance at port A and is reflected back to all ports

- patch panel - demountable coupler

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• Wave multiplexors

• Optical connectors

Passive DWDM module        •32, 16 passive channels DWDM Mux/Demux •100GHz (0,8nm) ITU Grid, C Band •Transparent transmission (protocol independent) •secure physical isolating between channels •minimal insertion loss •fully passive component (without power supply) •High density of ports(http://www.technicomms.sk/)

• even there are switches - they operate as routers – they redirect opt. signal into choosed direction; their fundamental components are lens and optical prisms; there can be bypass switches and 2-state switches

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Active optical components

1. Optical sources (tunable lasers, diodes)

2. Optical detectors

3. Optical amplifiers

4. WADM – Wavelength add/drop multiplexor- programable optical switching array – between 2 optical links with WDM support

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Component Typical value [dB] Number/ length

Opt.fiber 1550nm Fμ=0,27 dB/km Fσ=0,05 L = 0÷30 km

Opt.fiber 1310nm Fμ=0,7 dB/km Fσ=0,15 L = 0÷30 km

Coupler Sμ=0,1 dB Sσ=0,05 n=1,2÷2/km;

n≥2

Connector Cμ=0,4 dB Cσ=0,1 n ≥2

Distrib.point 1:2 Dμ=3,8 dB Dσ=0,50

-

1:4 Dμ=6,7 dB Dσ=0,42

1:8 Dμ=9,8 dB Dσ=0,55

1:16 Dμ=13,1 dB Dσ=0,67

1:32 Dμ=17,0 dB Dσ=0,90

WDM Wμ=0,5 dB Wσ=0,1

Tab.3.3.2 Typical values of attenuation (insertion loss) of optical components in OAN (μ –mean value, σ-st. deviation) [3]

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Duplex in OAN:

-2 fibers Space Division Multiplex (SDM) – 1 fiber for each direction

-1 fiber with time alternating of directions (ping-pong system) – TCM (Time Compression Multiplex)

- 1 fiber with 2 wave length in the optical windows 1310 a 1550 nm – WDM

Examples of professional optical access systems:

Alcatel 1570 – narrowband optical access system in PON

Alcatel 1575 (HYTAS – Hybrid Telecommunication Access System) – with AON, it allows incorporate metallic circuits

Siemens Fast Link – hybrid

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OPTICAL RELAY LINKS

- transmission through free space, analogous to RRL (Radio Relay Links)

-advantages ....., disadvantages if compared to radio links...,

- the parts of opt. relay systems ...

- applications: ...

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Referencie:

[1] http://www.oftc.usyd.edu.au/edweb/devices/networks/coupler8.html[2] V.Kapoun: Přístupové a transportní síte. VUT v Brně, 1999.[3] Vaculík: Prístupové siete. ŽU v Žiline, 2000.[4] J. Vodrážka: Přenosové systémy v přístupové síti. ČVUT, 2003.[5] J. Turán: Optoelektronika, Harlequin (s podporou FEI_TU-KE), 2002.