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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 = Optical Access Network

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

- 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 Function 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)

FTTO (...Office)

FTTCab (...Cabinet)

*************************************************

FTTE (... Exchange)

- 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. whre 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) - equipments with power supply

-passive one (PON) – 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 fibers, 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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Examples of fiber technology (by EMTELL)

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Optical fibers and their properties

- max. modulation frequence band

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]

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

...from optoelectronics:

boundary

100% reflection

21source: 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:

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optical fibers ...

Fig.3.3.15 Attenuation dependance on wavelength ane others 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 Properties of standard 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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Wavelength multiplexors

Couplers - simple, or demountable

Optical connectors

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- patch panel - for connecting optical fibers and for their cover and screening

- ODF – Optical Distribution Frame – for controled connecting of fibers

source: http://www.huihongfiber.com/fiber-test-equipment.html

sources: http://www.b2bfiberoptic.com/04-01002.htm

http://www.alibaba.com/product-gs/212149133/Patch_Panel_Fiber_Optic_Patch_Panel.html

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Component Typical value of attenuation [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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odbočka

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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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Duplex in OAN:

-2 fibers Spice 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

- FOS - Free Space Optics

- 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.