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Network Infrastructures – a.a. 2008-2009 Lecture 0 pag. 1
Network Infrastructures
A.A. 2014-2015Prof. Francesca Cuomo
Towards Fiber to the X (FTTX): Passive Optical Networks
Francesco Matera
Responsabile Area Tecnologie Reti di Nuova Generazione
[email protected] ; +39 06 5480 2215
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Outline
• Why FTTx
• How FTTx: PON
• Principles of Optical Fibre Systems
• PON characteristics (APON, BPON, EPON, GPON)
• Future: WDM PON
• Application
• Market (cost, unbundling)
Main source: Project EU E-Photon/One+, Lessons from Prof. A. Pattavina, G. Maier, Politecnico di Milano
Access/backhoul
10 Gbps
1 Gbps
100 Mbps
10 Mbps
1 Mbps
200 m50 m 500 m 1 km 5 km 15 km+
Fiber
Microwave
LMDS
Optical Wireless
xDSL
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PSTN access-networkPhysical architecture
Primary network
• High sharing• Cost minimization
Secondary network
• Flexibility• Branching
Cables
• Primary 2400-2000 pairs In duct or pipe
• Secondary 100-10 pairs Trenched or aerial
Cascading more stages of cabinetsis possible but rare
Distribution point (box)Distribution
cabinetPrimary cable
Twisted pairCentral office
Feeder / primarynetwork
Distribution / secondarynetwork
Homenetwork
Dedicated / leased line
Secondary cable
Telecom access networks
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Optical Fiber: Attenuation
Single Mode Fiber (SMF) to achieve large distances
• ITU G.652 SMF (STD) “water peak” attenuation renders the 1360nm–1480nm spectrum unusable for data transmission
• ITU G652c/d SMF (ZWP) “zero-water peak”
800 900 1000 1100 1200 1300 1400 1500 1600 1700
0.5
1.0
1.5
2.0
2.5
3.0First
Window SecondWindow
ThirdWindow
ATT
ENU
ATI
ON
(d
B/k
m)
WAVELENGTH (nm)
1310nm
1550nm
850nm
STD SMF
ZWP SMF
Optical Fiber: Chromatic Dispersion
Causes signal pulse broadening
Dispersion
+
-
Wavelength [nm]
Waveguide Dispersion
Total Dispersion
Material Dispersion
1200 1400 1600Zero at 1310 nm
Single-mode optical fiber
Shorter Wavelengths
Longer Wavelengths
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Lasers Diodes (LD)
Fabry-Perot (FP)
• Cheap
• Noisy Sensitive to chromatic dispersion
• Used on 1310 nm
Distributed Feedback (DFB)
• More expensive
• Narrow spectral width Less sensitive to chromatic dispersion
• Used on 1550 nm (or 1310 nm)
Simple FP
mirror
gain
cleave
+
-
mirror
gain
AR coating
+
-
DFB
Passive Splitters
1x2 Splitter 1xN Splitter
• The basic element consists of two fibers fused together
• Every time the signal is split two ways, the signal is reduced by 10log(0.5)=3dB
• Loss ~3dB x log2(#ONUs)
3.4dB3.7dBSplitter 1x2Low-loss Conventional
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Photodiodes (PD)
PIN Photodiodes
• Good optical sensitivity (-22 dBm)
• Silicon for shorter ’s (eg 850nm)
• InGaAs for longer ’s (eg 1310/1550nm) Avalanche Photodiodes (APDs)
• Higher sensitivity (-30 dBm)
• Primarily for extended distances in Gb/s rates
• Much higher cost than PIN diodes
Transceiver Assumptions
Upstream (@1310nm) Power Budget = 30 dB
Downstream (@1490nm) Power Budget = 22 dB
-22 dBm0 dBmONU (FP+PIN)OLT (DFB+APD) -30 dBm1 dBm
RX SensitivityTX Power
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Fiber installation
La microtrincea come semplice ed economica soluzione per la diffusione della fibra ottica nella rete di accesso(from HighBand)
Soffiaggio della fibra (ERICSSON)
30-40 K €/km per microtrincea
DSLAM
Cavo
PrimoArmadio
SecondoArmadio
500-1000 m 100-300 m 50-200 m
Centrale
Switch/Router
PrimoArmadio
SecondoArmadio
a) Best cuurent architecture
DSLAM
Fibra ottica
b) Fiber to the cabinet
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Switch/router
PrimoArmadio Secondo
ArmadioFibra ottica
c) Fiber to the curb
DSLAM
Switch/router
PrimoArmadio
SecondoArmadioFibra ottica
d) Fiber to the building
D
Switch/router
PrimoArmadio
SecondoArmadioFibra ottica
e) Fiber to the home
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Centraloffice
Centraloffice
Centraloffice
Curbswitch
Splitterottico
a)
b)
c)PON
Access capacities
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Core
GbE based: FASTWEB
Daisy chain architecture
First case in Europe:Fastweb 2000FTTH: Accesso Residenziale
FTTB: Accesso Business
Verso la Backbone
RouterPABX
LAN
Technical room
Verso la Backbone
IP switch
HAG
Uplink Fibra
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FTTx = Fiber-to-the-x
FTTH - Home
FTTC - Curb
FTTN - Node or Neighborhood
FTTP - Premise
FTTB - Building or Business
FTTU - User
FTTZ - Zone
FTTO - Office
FTTD - Desk
Basic PON operations
The optical line terminal (OLT) broadcasts data downstream on 1,510 nm andthe ONTs burst data back upstream on 1,310 nm in their assigned time slots.
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Photonics Evolution
Distanze
10 m 100 m 1 km 10 km 100 km 1000 km e oltre
2008
2010
2015
ADSL2+
VDSL/2 FTTP
VDSL2 FTTB
FTTH Provider backbone transpoortT-MPLS
VPLSMPLS
Optical Packet switching
Optical burst switching
Conversione lunghezza d’onda
GbE SDH
OTN
FTTH
WDM
L3
L2
L1
Time vs. Spectrum Sharing
Downstream point-to-multipoint network
• The OLT manages the whole bandwidth Upstream multipoint-to-point network
• ONUs transmit only towards the OLT
• ONUs cannot detect other ONUs transmissions
• Data transmitted by ONUs may collide
Need of a channel separation mechanism to fairly share bandwidth resources
TDMATime Division Multiple Access
WDMAWavelength Division Multiple Access
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PON Overview
TDM-PONs
• Standardized
• Use few wavelengths (typically 2 or 3)
• Low cost and mature devices (splitters, lasers, etc.)
• Limited power budget Maximum distances 20km, Split ratios 64
• Traffic distribution Broadcast scheme in downstream TDMA techniques in upstream
• Examples: APON/BPON, EPON & GPON WDM-PONs
• Proposed in literature and/or demonstrated
• Introduce WDM techniques and devices (AWG)
• Long-reach and bandwidth
• Examples: CPON, LARNET, RITENET, Success-DWA…
Downstream Traffic Scheduling
OLT
A
B
C
Passive Splitter
A B C B A B C B
• OLT schedules traffic inside timeslots -Time Division Multiplexing (TDM) scheme
• Time slots can vary from s to ms
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Upstream Traffic
OLT
ONU
ONU
ONU
Passive Splitter
• All ONUs share the same upstream channel ONUs cannot exchange data directly
Collisions may occur at the splitter/combiner
Upstream Traffic Scheduling 2/4
• In general, PON standards propose Time Division Multiplexing Access (TDMA) schemes Upstream time slicing and assignment
OLT
ONU
ONU
ONU
Passive Splitter
B BA B C B
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Upstream Frame Reception
• The OLT receives frames with different powers Much difficult to recover synchronism (clock and data recovery)
Burst Mode Receiver (complex) @ OLT• Sets 0-1 threshold on a burst basis
OLT
A
B
C
Passive Splitter
BB A
7 km
3 km
1 km
Automatic Gain Control to adjust 0-1 threshold at the beginning of each received burst
Evolution of the standards
10 GB EPON
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Fiber in the loopPON standardization: a brief history
ATM PON (A-PON)
• Traffic is carried using ATM raw-cell format and framing• 1982: idea of PON (British Telecom)• 1987 – 1999: PON testbeds by BT, Deutsche Telekom (Eastern Germany), NTT
(Japan), BellSouth (Atlanta, USA)• 1995: 622 Mbit/s APON testbed (RACE BAF project)• 1996: beginning of Full Service Access Network (FSAN) works• 1997-’98: ACTS BONAPARTE and EXPERT/VIKING projects
Broadband PON (B-PON)
• APON system is standardized by ITU-T with a new name to indicate that thePON can offer full broadband service and not just ATM
• Line rates: 155 Mbit/s symmetrical or 622/155 Mbit/s down/upstream;ONU/OLT max distance: 20 km; max. # ONUs: 64
• 1998-’00: ITU-T G.983.1 (physical aspects) and G.983.2 (ONT managementand control)
• 2001-’02: other ITU-T G.983.x and Q.834.x, e.g. G.983.4/.7: Dynamic Bandwidth Assignment (DBA), providing statistical multiplexing ( more users per ONU) and Quality of Service
(QoS) enforcement G.983.3: adoption of WDM to increase capacity or to carry video signals
Fiber in the loopPON standardization: a brief history
Ethernet PON (EPON)• Traffic is carried using Ethernet framing
Cheaper user equipment then BPON Ethernet much more widespread than ATM
• Higher subscriber rates (up to 1.25 GbE symmetrical), 16 ONU (power budget)• 2001: IEEE 802.3ah Study Group “Ethernet in the First Mile (EFM)”• First documents in Sept. 2003)• 2004: final approval of Standard IEEE 802.3ah
Gigabit-capable PON (G-PON)• Traffic is carried by using different possible framings: ATM (G.983 base) or via
G-PON Encapsulation Method (GEM), which can interface SDH (G.707 base) orEthernet (IEEE802.3 base).
• Various line rates, up to 2.4 Gbit/s symmetrical, ONU/OLT max distance: 20km; max. # ONUs: 64-128
• 2001: activity initiated by the FSAN group• 2003: ITU-T G.984.x
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Layer 1: physical layer
Layer 2: data link layer
10Mb/s 100Mb/s 1Gb/s 10Gb/s
IEEE802.2 logical link control
IEEE802.1 bridging
IEEE802.3Ethernet
MAC layer
IEEE802.4Token busMAC layer
802.3ah EFM
Physical layer
IEEE802.5Token ringMAC layer
IEEE802.6MAN
MAC layer
IEEE802.11wireless
MAC layer
Physical layer
Physical layer
Physical layer
Physical layer
• EPON started to be standardized by IEEE 802.3ah EFM since 2001, it
was ratified in 2004
Ethernet Standards in EPONs
Ethernet PONs (EPONs)
All packets carried in EPON are encapsulated in Ethernet frames
• Support for variable size packets Similar wavelength plan to BPON
Maximum bit rate is 1Gbps MAC-MAC (1.25 Gbps at the physical layer with 8b/10bline coding)
Minimum number of splits is 16
Maximum reach is• 10 km (FP-LD @ ONUs, limited by dispersion in downstrea for G.652)
• 20 km (DFB-LD @ ONUs)
Different configurations are allowed
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OLT
OLT
OLT
OLT
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
1) Tree Topology
(2) Ring Topology
(3) Tree with Redundant Trunk
(4) Bus Topology
EPON Configurations
EPON Downstream Traffic
Similar to a shared medium network
Packets are broadcasted by the OLT and selected by their destination ONU
ONU 3
OLT
21 13
Header Payload FCS
802.3 frame
21 13
1 1
2
3
USER 2
USER 3
USER 1
ONU 2
ONU 1
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EPON Upstream Traffic
ONU 1
ONU 2
ONU 3
USER 1
OLT
FCSHeader Payload
3
802.3 frame
Time slot
33
333
USER 2
USER 3
222
11
11
ONUs synchronized to a common time reference
Centralized arbitration scheme OLT based
OLT grants access to ONU for a timeslot
• Several Ethernet packets
Frames Buffer
The Multi-Point Control Protocol (MPCP)
Original Ethernet MAC protocol cannot operate properly in the upstream channel(no collision detection) since each ONU cannot hear other ONUs
MPCP (Multi-Point Control Protocol) is a new function of the MAC control sublayer.It is developed to support dynamic capacity allocation but the algorithms are anequipment vendors choice (Dynamic Bandwidth Allocation - DBA)
• In-band signalling• Messages (64 bytes)
GATE REGISTER REGISTER_REQUEST REGISTER_ACK REPORT
4
40
4
2
2
6
FCS
Data/Reserved/Pad
Timestamp
Opcode
Length/Type 88-08
Source Address
Destination Address 6
MSBLSB
b7b0
Octets
Bits within frame transmitted left-to-right
Octets within frame transmitted top-to-bottom
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Autodiscovery mode
3 control messages:
• Register, start message sent by OLT;
• Register_Request, answer message from ONUnot registered yet;
• Register_Ack, message by OLT that allowsONU registration.
GPON Standardization
Feb. 2004G-PON TC layer spec.
(Transmission convergence layer specification)G.984.3
Mar. 2003G-PON Physical Layer spec.
(Physical Media Dependent (PMD) layer specification)
G.984.2
Mar. 2003G-PON service requirements
(General characteristics)G.984.1
AdoptionOutlineITU-T
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G.984.1 Service Requirements
Downstream video wavelength (1550 –
1560nm) may be overlaid
Downstream: 1480 – 1500nmUpstream: 1260 – 1360nm
Wavelength allocation
Max. 64 in physical layerBranches
Max. 60 kmLogical reach
Max. 20 km or max. 10 kmPhysical reach
1.25Gbit/s symmetric or higher (2.4 Gbit/s). Asymmetric with 155/622Mb/s upstream
Bit rates
TargetItem
GPON Encapsulation Mode (GEM)
GEM provides a Generic Frame where to carry both TDM and packet traffic overfixed data-rate channels
• Similar Generic Framing Procedure (GFP) used inSDH/SONET
A Generic Frame consists of:
• a core header
• a payload header
• an optional extension header
• a payload
• an optional frame check sequence (FCS).
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Downstream Frame Structure 1/3
It consists of
• a Physical Control Block Downstream (PCBD)
• the ATM partition (N×53 bytes)
• the GEM partition
PCBdn+1
PCBdn+2
Payload n Payload n+1PCBd
n
TP-Frame = 125 µs
TDM & Data Fragmentsover GEM Section
“Pure” ATM cellsSection
N * 53 bytes
GPON Header
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Technical Standards Comparison
Technology Standard Downstream/Upstream Bandwidth # ONT served Lambda Framing/
Protocol Distance
APON/BPON(ATM PON/ BroadbandPON)
ITU-T G.983.x
155, 622 or 1244 Mbit/s down
155 or 622 Mbit/s up
Limited by power budget and ONU addressing limits:
16 to 32 splitter
1490 nm Down
1310 nm Up
(1550 nm Down for RF video )
ATM 20 km
GPON(Gigabit PON) ITU-T G.984
1.2 or 2.4 Gbit/s down
155, 622, 1.2 or 2.4 Gbit/s up
Up to 64(physical)
Up to 128 (logical)
1490 nm Down
1310 nm Up
(1550 nm Down for RF video)
GEM: G-PON Encapsulation
Method (supports Ethernet), ATM
10/20 km (up to 60
km )
EPON
(Ethernet PON)*IEEE 802.3ah Symmetric 1.25 Gbit/s Up to 16
1550 nm Down
1310 nm UpEthernet 10/20 km
10GEPON(10 Gigabit EthernetPON)
IEEE 802.3av (Working
Task Force)
10 Gbit/s down 1 Gbit/s up
(symmetric 10 Gbit/s in the future?)
32 (maybe more?)
1480-1500 nm Down ?
1260-1360 nm Up ?
1550-1560 Video overlay ?
Ethernet 20 km
Transmission Efficiency
0
200
400
600
800
1000
1200
1400
EPON GPON BPON
Mb
/s
scheduling OH : framedelineation
scheduling OH : PHY burst OH
scheduling OH : controlmessages
payload encapulation OH
line coding
payload
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Header’s Comparison
Guard Preamble DelimiterGPON
EPON
min. 25.6 ns
typ. 35.2 ns
typ. 16.0ns
min. 76.8 ns
Data
Laser turn on time
AGC, CDRsetting time
Data
max. 400 ns max. 400 ns
Guard Preamble DelimiterBPON
min. 4 bits
typ. 12 bits
typ. 8 bits
24 bits
Data
AGC: Automatic Gain Control; CDR: Clock and Data RecoveryLaser turn on time overlaps the laser turn off time of the previous burst
Laserturn off time
max. 400ns
Data
EPON costs about ~10% the cost of BPON/G
Simple WDM-PON
Number of ONUs limited by wavelengths
Point-to-point topology
Long-reach (almost point-to-point reach)
WDM Receiver
Receiver Array/Optical
Demux
AWG
1 x N
Receiver
ONUsWDM ModulatedSource
OLT
Central Office (CO)
λ1, λ2….λn
λN+1, λN+2….λ2N
λ1
λN+1
λN
λ2N
Transmitter
Receiver
Transmitter
.
.
Filter as Optical router
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B type1+1 protection of OLT
C type1+1 protection of PON
Protection Mechanisms
Cost-effective
Redundant feeder
Redundant OLT transceivers Most secure and expensive
Redundant feeder and drops
Redundant transceivers
TR
TR
TR
TR
TR
OLT ONU-1
ONU-2
ONU-n
・・
TR
TR
TR
TRTR
TR
TR
TR
OLTONU-1
ONU-2
ONU-n
・・
Carrier Ethernet for PON (EPON)
Centraloffice
c)PONNetwork
Carrier Ethernet: Processing from level 3 to 2Specific path for QoS
VLANTAG, VPLS, Q-in-Q, MAC in MAC, PBT
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Elements of a PON
STB
Rete Domestica
Sede d’UtenteRete SecondariaRete PrimariaCentrale Edificio
F.O.OLT
coppia inrame
coppia inrame
VDSL
VDSL
F.O.
coppia inrame
NTVDSL
F.O.
Cabinet
Curb
Building
Diramatore1:N
NodoATM
Rete CDN
V5.1V5.2
VB5.1VB5.2
PSTN/ISDN
ONU
ONU
OLT: Optical Line
VDSL: Very high bitrate Subscriber Loop
ONU: Optical Network UnitNT : Network Termination
STB: Set Top Box
NT
NT
International development overview
China• GPON and EPON are being tested in China : future PON growth mainly depends on Chinese market
evolution• Beijing, Wuhan, Shanghai e Guangzhou are the cities with the greatest FTTX deployment
Japan• The number of xDSL users has decreased for the first time at the end of 2006, while FTTH users have
grown by 10% in 2006 last trimester.• At the end of 2006, out of 26 million Broadband lines, FTTH accounted for 30% of the total amount.
South Korea• In July 2007, 500.000 FTTH users• Almost 4 million FTTB “apartment LANs”
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International development overview
USA
• Large average cable-length
• Large investments form cable operators, that account for arelevant share of the broadband market
• No unbundling required for new fiber infrastructures. Brazil, Colombia, Argentina, Chile
• Less than 300.000 FTTH users Australia, New Zeeland, Kuwait, Russia, United Arab Emirates, Pakistan
• Less than 2 million FTTH users
Ref: EXFO, may 2007
• Mostly in Northern Europe, local administrations are building the infrastructure, with equal access conditions for service providers
• The leading incumbents are deploying extended FTTCab/VDSL infrastructure plans.
• Sweden: more than 500.000 FTTH users
• France, UK: more than 600.000 FTTH users
• Italy : more than 250.000 FTTH users
• Denmark: more than 400.000 FTTH users
• Holland : more than 500.000 FTTH users
International development overview
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FTTx costs
FUB study on NGN economics
• 1400 Mega Euro for digital Divide end (connection of central office to babckbone)
• FTTC/B/H for all? No 2 Mb/s for all but 20 Mb/s for almost all and >50 Mb/s for many
• 10 million of users based on FTTB: total cost 15000 Mega Euro!
• Unbundling problems: – For OLO no PON, yes Point-to-point
– We say yes PON since:
» with logical unbundling now and WDM later!
» Too cost to include devices in central office and fibres in current ducts
» With PON we can shift OLO location from central office to l t b kb
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FUB Experiments on EPON
IP DSLAM
Line Simulator
J2
J3
J1
J4
C1
C2
C3
xDSL Access (ADSL2+)
FTTx Access (EPON)
OLT
ONU1
ONU2
ONU3
ONU4
Fast Ethernet
Doppino telefonico
Roma – Pomezia Anello Ottico 50 Km single mode 1550 nm
Optical link 50 m multi mode 850 nmEPON UP 1310 nmDOWN 1490 nm
IP DSLAM
Line Simulator
xDSL Access (VDSL)
NAS 3640 Switch ATM
ATM DSLAM
Line Simulator
Line Simulator
ATM DSLAM
xDSL Access (ADSL)
xDSL Access (SHDSL)Alcatel
ESS 7450
Juniper M10 e M10i
Cisco 3845
Alcatel ESS 7450
Cisco 3640
FiberHome OLT e ONU
ALCATEL IPDSLAM 7324
ASAM 1000 e 7300
Video Server
Anello ottico sperimentale Roma - Pomezia, distanze variabili tra 50 e 350 Km
Logical network by means of VPLS&VLAN Tagging
Un generatore ditraffico permette uncongestionamento traPE2 e OLT
Ethernet PON FiberHome
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Throughput in downstream
Congestione tra PE2 e OLT
Conclusions
• FTTx necessary for NGN
• PON is the best current solution
• Problems for investments and network properties