Access Networks
lectures 2008/09- winter term
Part 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:
star
1xN
coupler
star
coupler
tree (multiple star)
coupler
ring
OLT-optical line termination
ONU – optical network unit
bus
- Logical arch.: Tree
Fig.3.3.1
2
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)
OLT = Optical Line Termination – in the exchange end – connection to the
exchange
OAN
upstream
ONU
NT
ODN
user side
OLT
network
side
ONU
downstream
Fig.3.3.2 Function architecture of OAN
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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)
Exchange
*************************************************
FTTE (... Exchange)
Fig.3.3.3
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- on the metalic part (original POTS) there mostly operates VDSL system
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6
- 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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8
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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shared
source: http://access.feld.cvut.cz/view.php?nazevclanku=&cisloclanku=2006051702
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Management of access network
Fig.3.3.4: Reference configuration of OAN
Fig.3.3.5 Reference model of AN in the building
frequency
splitters
STB-SetTopBox
CPN-Customer
Premises Network
B...Broadband
NB...Narrow Band
NTE-Network
Termination
Equipment
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Reference configuration of OAN – continue: functional blocks OLT and ONU:
• system core
• functions of access to
services
Optical
distr.network
• common functions
Legend:
Switching
network
DCCF…
Fig.3.3.6.
OLT
TMF…
ODNIF…
TUIF…
SPF…
OAMF…
Optical
distr.network
User
ports
CaSMF…
SIF…
PSF…
Fig.3.3.7 ONU
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DCCF – Digital CrossConnect Function
TMF – Transport & Multiplexing Function
commutation and multiplex
ODNIF – Opt. Distrib.Network Interface Function
TUIF – Tributary UNIT Interface Function
- EOC function
- V5 interface
SPF – Signalling Processing Function
common functions
- conversion from signalling of switching system to
signalling in AN
-control functions with access to overall network management TMN,
and power supply
- OAMF – operation, administration and maintenance Function
- PSF - power supply function
C&SMF – Customer and Service Multiplex Functions
SIF – Service Interface Function
- 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
active DP
with EOC
several optical
segments
passive DP
without EOC
unique optical
segment
Fig.3.3.8 ODN classification according to DP (Distribution Point) properties
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Optical hardware
Multipoint (PMP)
networks OAN
active - AON
passive - PON
TDM
APON
Point-to-Point (P2P)
GPON
FDM
fibers
relay links -FSO
CWDM
EPON
Fig.3.3.9 Optical access equipment classification
PON technology
APON – 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
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hybrid -
Standards
ITU-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. 16
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
- on the base of Si-glass or plastic
- 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
- velocity of light propagation ~ 2/3 of c (in vacuum)
cladding
i – diffraction
index
core
Fig.3.3.10: Opt.fiber with both higher and lower order mode
- attenuation = {10log(P1/P2) } / length [dB/km]
- dispersion - (different velocity depending on λ,
also different i  limiting of λ band of fiber)
- max. modulation frequence band
[1]
Fig.3.3.11
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...from optoelectronics:
boundary
100% reflection
Obr.3.3.13 ...total reflection on the boundary
line of fibre-cladding (coating)
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[5]
Fig. Optical fibers types
source: http://en.wikipedia.org/wiki/Image:Optical_fiber_types.svg
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...from optics / physics:
n (or i) – diffraction index, v – velocity of propagation in solid material:
c
v   f .
n
n  r  r
-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:
v

k
 f
- phase velocity
-the group of waves with closed λ – they are moving by ‘group velocity’:

vg 
k
- other terms: critical impact angle, totale reflection, law of reflection
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The other properties of optical fibers:
2nd window
3rd window width
wave length
Fig.3.3.15 Attenuation dependance on wavelength ane others factors
optical fibers ...
[1]
reason of attenuation: presence and generation of OH ions,
Raileigh scatter („total“ border, edge)
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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
Tab.3.3.1 Properties of standard 1-mode fiber by G.652
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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“.
-or splitters

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
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Transmission Star Coupler
- the light arrives for instance at port
A and is split equally through ports
from G to L.
Reflection star coupler
-the light arrives for instance
at port A and is reflected back
to all ports
Fig..3.3.17 - a,b,c
- patch panel - demountable coupler
[1]
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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
sources: http://www.b2bfiberoptic.com/04-01002.htm
http://www.alibaba.com/productgs/212149133/Patch_Panel_Fiber_Optic_Patch_
Panel.html
- ODF – Optical Distribution Frame – for controled connecting of fibers
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source: http://www.huihongfiber.com/fiber-test-equipment.html
Component
Typical value of attenuation Number/
[dB]
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.
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