PON

Passive Optical Networking

Objective

At the end of the course, you’ll be able to …

� understand how fibers work, and explain which components are used in an

optical relay system

• internal reflection, transmitter, amplifier, receiver, splitter, …

� explain the basic properties of a passive optical network

� describe the functions of the components present in a PON based network

� correctly use basic PON terminology

3

Table of Contents

1. Optical fiber fundamentals

2. GPON fundamentals

3. PON standardisation

4

Optical Fiber Fundamentals1

5

Advantages of fiber

� Extremely high bandwidth

� Smaller-diameter, lighter-weight cables

� Lack of crosstalk between parallel fibers

� Immunity to inductive interference

� High-quality transmission

� Low installation and operating costs

No Interference

Large capacity

6

Optical fiber structure

Core

• thin glass center of the fiber where the light travels

Cladding

• outer optical material surrounding the core that reflects the light back into

the core

Coating

• plastic coating that protects the fiber from damage and moisture

7

Optical fiber classification

glass

• glass core – glass cladding

• lowest attenuation

• most widely used

plastic

• plastic core – plastic cladding

• highest attenuation

• pioneered for use in automotive industry

plastic-clad silica

• glass core – plastic cladding

• intermediate attenuation

8

Optical fiber types

G.651 – MMF – Multi-mode fiber

• large(r) core: 50-62.5 microns in diameter

• transmit infrared light (wavelength = 850 to 1,300 nm)

• light-emitting diodes

G.652 – SMF – Single mode fiber

• small core: 8-10 microns in diameter

• transmit laser light (wavelength = 1,200 to 1,600 nm)

• laser diodes

8 – 62.5 um125 um

CladdingCore

Coating

245 um

9

Total internal reflection

Concept

• light travels through the core constantly bouncing from the cladding

Distance

• a light wave can travel great distances because the cladding does not

absorb light from the core

Signal degradation

• mostly due to impurities in the glass

core

cladding

acceptancecone

10

Hit me baby one more time

Atoms have a core with circling electrons

o What happens when a light photon bumps into an electron ?

Electron is disturbed but falls back onto it’s original level : energy is released

into a certain direction = scattering

Electron is disturbed and reaches a higher energy level : energy is lost

= absorption

ray of light

11

The world of wavelengths

Light is transported as a wave.

o The length of the wave determines the type of light (infrared, ultraviolet, …)

12

Attenuation as function of wavelength

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.8

Wavelength (microns)

1.7

2.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Att

enuati

on (

dB/Km

)

0,85 µ

band

1,30 µ

band

1,55 µ

band

0.0

13

Fiber optic relay system

Optical transmitter

• produces and encodes the light signal

Optical amplifier

• may be necessary to boost the light signal (for long distances)

Optical receiver

• receives and decodes the light signal

Optical fiber

• conducts the light signals over a distance

Tx RxAmplifier

Electrical ElectricalOptical Optical

14

Transceiver

Definition:

• a transmitter and a receiver

in a single housing

Practical implementation:

• transceivers typically come as SFP

• Small-Form-factor Pluggable unit

Rx

Tx

15

Lightwave modulation

Digital

• light intensity does change in an on/off fashion

• NRZ - non return to zero

0 - weak optical signal

1 - strong optical signal

Analog

• light intensity changes continuously

16

Fiber interconnections

Interconnect fibers in a low-loss manner

• is a permanent bond needed ? – splice !

• is an easily demountable connection desired ? – connector !

Terminal A Terminal B

permanent joint

demountable joint

SPLICE

CONNECTOR

0.3 dB0.3 dB

0.1 dB 0.1 dB 0.1 dB 0.1 dB 0.1 dB

17

Joining fibers – Fiber alignment

bad alignment

• cores are not centered

• big power loss

good alignment

• cores are centered

• small power loss

18

angular physical contact

• some back reflection

• (small) return loss

straight physical contact

• lots of back reflection

• (big) return loss

Joining fibers – Fiber orientation

19

Joining fibers – Connectors

Properties

• good alignment/correct orientation

• present at the termination point of the fiber

• always introduce some loss

Connector types

• amount of mating cycles

• LC, FC, SC, …

Color code

• APC – green

• PC – blue

Theoretical loss:

0.3 dB

Shouldn’t be mixed

20

Connectors - Couplers

SC/UPC SC/APC ST/APC

Couplers

21

Joining fibers – Splices

Mechanical splicing

• aligning and orienting the fibers,

• then clamp the fibers in place

Fusion splicing

• aligning and orienting the fibers,

• then fuse (melt) the fibers

• using an electric arc

typical case used to enclosefiber optic splices in an

outside plant environment

Theoretical loss:

0.1 dB

Fusion splicer

22

Optical power splitters

Optical splitters …

• typically divide an optical signal …

from a single input

into multiple (e.g. two) identical output signals

• and generally provide

a small optical loss

to the signal passed through it

λ1

λ1

λ1λ2

λ2

λ3

λ3

3.5 dB

insertion loss

23

Optical wavelength splitters

Wavelength Division Multiplexing …

• enables the combining of …

o multiple wavelengths

o into one single fiber

Depending on the design, an optical wavelength splitter …

• typically provides …

o a small to medium loss

o to the signals passed through it

0.3 dB loss

λ1

λ2

λ1

λ2

insertion loss

24

PON benefits

� purely passive fiber plant

• low maintenance costs and high reliability

� shares feeder fiber over multiple users

• less fibers needed, less ports needed at CO

� fiber is virtually not limiting the bandwidth

• much higher bandwidth x distance than copper networks

� fiber’s bandwidth can be further exploited by WDM or equipment

upgrade

• installed fiber infrastructure is future-proof

� PON offers bundled services over a single fiber

• triple play – voice / data / video

25

PON deployment scenarios – FTTx

OLT

Network

ONUADSL ( < 6 KM )

< 8 Mbit/s

FTTEx

ONU

ADSL/VDSL ( < 1 KM )

< 26 Mbit/s

FTTCab

VDSL ( < 300 M )

< 52 Mbit/s

FTTC

ONT

FTTH/B

Central Office

XNT

XNT

XNT

ONU

26

GPON fundamentals2

27

Aggregation

Transmit

Receive

Customer Premises Equipment (CPE)

(P2P)

Point-to-Point

1:1

Two Basic FTTH technologies

x4

(P2MP)

Point-to-Multi-Point used in GPON

1:64 to 1:128

Splitter

Optical Line Terminal (OLT)

Downstream

Upstream

Optical Network Terminal (ONT)

1490

1310

SubscribersLESS SPACE, LESS FIBRES, LESS DUCT SIZE

28

Definition - Feeders, Distribution, Drops

Access Point

Feeders

(primary)

Distribution

(secondary)

DropsPOP

ActiveActive

Passive

29

PON properties

PON – Passive Optical Network

• passive components

o splitters + WDM-device

• star topology

o p2mp – point to multipoint

Ranging distance

• 60 km maximum logical reach

• 20 km differential distance

Split-ratio

• Minimum 64 subscribers (or more)

PON

No Equipment No Power

30

PON lambdas

Voice and data over a single fiber

• two wavelengths in opposite directions

Video

• one wavelength in downstream direction

Splitters

1490 nm

1310 nm

Data path

1550 nm

Video path

Line rate flexibility

2500 Mb/s

1250 Mb/s

V-OLT

P-OLT

31

Splitter - Types

PLC – Planar Lightwave Circuit- Built into glass waveguides- Solid state- No mechanical parts- Compact-Splits: 1x4, 1x8, 1x16, 1x32-Splits: 2x4, 2x8, etc

FBT – Fused Biconic Taper-Two fibers fused to create a split- Typical fusion of 2, 3 or 4 fibres- Splits in cascade

Type 1: FBT Type 2: PLC

32

Splitters – Example

Available in various splice trays and terminals

Available with factory terminated pigtails

CONNECTORISEDSPLICED

-- Flexible

-- Patch cords included

-- Easy to replace

-- Cheap

-- Maintenance free

-- Skilled technician

3M3M

33

Optical power budget

� loss in splitters

• cascaded splitter can be used

e.g. 1:4 splitter followed by 1:8 splitter or vice versa

• so a one-step 1:32 splitter can be used

� loss in WDM coupler

� loss per km fiber

� loss in connectors

� loss in splices

PON

Distance depends on loss in different components:

34

Splitter – Optical Budget

Example:Splitter 1 x 8

InputFiber

OutputFiber

3.5dB

3.5dB3.5dB Optical Splitters Loss [dB]

Splitter 1 x 64 20.1

Splitter 1 x 32 17.4

Splitter 1 x 16 13.8

Splitter 1 x 8 10.5

Splitter 1 x 4 7.0

35

Data transceiver specifications (class B+)

+5.0

P (dBm)

+1.5

+5.0

P (dBm)

+0.5

-8.0

P (dBm)

-27.0

-8.0

P (dBm)

-28.0

1490 nm

1310 nm

path penalty: 0.5 dB

path penalty: 0.5 dB

Downstream budget:

+1.5 – (-27) – (0.5) = 28 dB

Upstream budget:

+0.5 – (-28) – (0.5) = 28 dB

Tx level

Tx level

Rx level

Rx level

0.30 dB/km

0.42 dB/km

36

Optical power budget – Data

Example:

• budget: 28 dB

• 16 way splitter loss: 13.8 dB (theoretical. 12dB)

• connector+splicing loss: 3 dB (24*0.1 dB + 2*0.3 dB)

• aging: 1 dB

• attenuation:

o 0.30 dB/km – downstream

o 0.42 dB/km – upstream

Distance:

• (28 – 13.8 – 3 – 1) / 0.42 = 10.2 / 0.42 = 24.28 km

Interpretation:

• for a 1:16 split, the max distance of an ONT is 24 km

37

Data transceiver specifications (class C+)

+7.0

P (dBm)

+3.0

+5.0

P (dBm)

+0.5

-8.0

P (dBm)

-30.0

(**)

-12.0

P (dBm)

-32.0

1490 nm

1310 nm

path penalty: 1 dB (*)

path penalty: 0.5 dB

Downstream budget:

+3 – (-30) – (1) = 32 dB

Upstream budget:

+0.5 – (-32) – (0.5) = 32 dB

Tx level

Tx level

Rx level

Rx level

0.30 dB/km

0.42 dB/km

(*) Accounts for DS dispersion effects up

to 60km reach

(**) ONT sensitivity in C+ mode with FEC

38

Video transceiver specifications

+18.5

P (dBm) P (dBm)

-4.9

1550 nmDownstream budget:

+18.5 – (-4.9) = 23.4 dB

Tx levelRx level

39

Optical power budget – Video

Example:

• budget: 23.4 dB

• 16 way splitter loss: 13.8 dB (theoretical. 12dB)

• connector+splicing loss: 3 dB (24*0.1 dB + 2*0.3 dB)

• aging: 1 dB

• attenuation:

o 0.25 dB/km - downstream

Distance:

• (23.4 – 13.8 – 3 – 1)/0.25 = 22.4 km

Interpretation:

• for a 1:16 split, the max distance of an ONT is 22.4 km

40

Eric

Maximum range per splitter - configuration

1:64

1:8

1:16

1:32

38 km

30 km

21 km

14 km

1:2

1:4

splitting best

case

worst

case

1 : 64 14 km 10 km

1 : 32 21 km 15 km

1 : 16 30 km 23 km

1 : 8 38 km 30 km

ITU-T G.984

Standard

B+ Laser

41

GPON protocol layers and formats

GEM – GPON Encapsulation Method

• Ethernet + TDM

ATM – Asynchronous Transfer Mode

VG

optical (TDM/TDMA)

Ethernet[AAL5] + Ethernet

[AAL2] + Ethernet + TDM POTS/VF

OLTONT

BAS

42

Data Transmission : DOWNSTREAM

Standardized by ITU-T in G.984.x recommendation

Communication between P-OLT and ONT

Downstream : broadcast traffic – use encryption for security (AES)

?

43

Data Transmission : UPSTREAM

ONTs are located at different distances from Central Office

Upstream : same wavelength + same fiber

– Use Time Division Multiple Access (TDMA)

How ?

– Distance OLT – ONT has to be measured

– Timeslots are allocated according to distance

– ONTs only send upstream according to granted timeslot

44

Distance ranging – Why?

deliberately putting equalization delay infor the purpose of avoiding collisions

20 km

20 km

15 km

45

Distance ranging explained

time

distance

t1

t2

?

Ot

= (t2 – t1-Ot)/2

Assume this is 75 µs

Cfiber = 200.000 km/s

?

? = 15km

�

�

�

�

�

46

GPON frame format

ATM-segment (option)

downstream frame – 125 us

GEM-segment

upstream frame – 125 us

ONU1 ONU2 ONU3 ONU4 ONU5

PCB GEM-packetATM-cell

47

DOWNSTREAM : Continuous mode operation

Downstream – there’s always a signal

• even when there’s no user data to pass through

• except when the laser is administratively turned of

downstream frame

Tx Rx

continuous mode Tx continuous mode Rx

48

GPON frame format – Downstream

ATM-segment (option) GEM-segment

Psynch Ident PLOAMd BIP PLend PLend US BW Map

Physical Control Block

4 bytes 4 bytes 13 bytes 4 bytes 4 bytes N*8 bytes

1 byte

49

GPON frame format – Downstream (cont.)

Psynch Ident PLOAMd BIP PLend PLend US BW Map

Physical Control Block

N*8 bytes

… AllocID … CRCAllocID Flag SStart SStop CRC

12 bits 12 bits 2 bytes 2 bytes 1 byte

Entry for ONT#1 Entry for ONT#N

50

GPON frame format – Downstream (cont.)

US BW Map

3 entries

ONT1 slot 75 slot 240

AllocID Start Stop

ONT2 slot 280 slot 400

AllocID Start Stop

ONT3 slot 430 slot 550

AllocID Start Stop

upstream packet timingguard timeguard time

75 240 280 400 430 550slot times: time

51

UPSTREAM : Burst mode operation

Upstream – there’s only a signal when an ONT needs to send

• when no ONT has info to send, there’s no light on the fiber at all

• between 2 consecutive bursts, a guard time is needed: 26 ns

upstream frame

Rx Tx

burst mode Rx burst mode Tx

52

GPON frame format – Upstream

ONU1 ONU2 ONU3 ONU4 ONU5

Header Payload

PLOu PLOAMu DBRu

Physical

layer

overhead

Physical

layer

OAM

Dynamic

bandwidth

report

53

GEM = GPON Encapsulation Method

GEM allows for

• point-to-point emulation

• payload fragmentation (efficiency)

GEM allows native TDM transport

• E1/T1, E3/T3 raw format

12 bits 13 bits12 bits 3 bits

TDM

Ethernet PayloadMACDA MACSA

Type/

LengthFCS

GEM header

GEM encapsulation

payload

L bytespayloadCRCPTIPortIDPLI

L bytes

54

PON standardization3

55

ITU-T standards for GPON

� G.984.1 – GPON service requirements

• specifies line rate configurations and service capabilities

� G.984.2 – GPON physical medium

• specifies transceiver characteristics

per line rate and per ODN class

including burst overhead for each upstream line rate

� G.984.3 – GPON transmission convergence

• specifies transmission convergence protocol, physical layer OAM, ranging

mechanism

� G.984.4 – GPON ONT management control interface

• based on OMCI for BPON, taking GPONs packet mode into account

• phased approach to achieve interop (FSAN)

Alcatel-Lucent was the first GPON supplier to disclose its OMCI implementation details

56

PON

OMCI – ONT Management Control Interface

� a method to manage ONTs from the OLT

• this includes configuration, fault and performance management

� each ONT and the OLT has it’s own OMCI channel

• bandwidth is allocated at PON creation time

� protocol?

• the OMCI protocol

57

ITU-T G.984.x framework

Ethernet

TC adaptation sublayer

Framing sublayer

PON-PHY

C/M application

PLOAMOMCI

Voice/Data/Video

Embedded OAM

……

G.984.3 GTC

G.984.2 PMD

G.984.1 General characteristics

G.984.4 OMCI

58

Redundancy

� ITU-T G.984.1 specifies 3 types of redundancy between OLT and ONT

• Type A : spare fiber, no additional LTs or ONTs

• Type B : redundancy to the splitter : redundant LTs and feeder fibers to the

first splitter

• Type C: redundancy through the entire path: redundant LTs, fibers,

splitters, ONTs

** Separate geographical paths required for two feeders to avoid simultaneous fiber cuts **

59

PON Feeder Redundancy

Alcatel-Lucent currently implements partial Type B redundancy (Type B-)

• 1+1 redundant feeder fibers from the LT PON to the optical splitter

• Fiber-only protection: redundant fiber can be used in case the other one

fails

** Separate geographical paths required for two feeders to avoid simultaneous fiber cuts **

• No redundant LTs - no protection against HW & SW failures on the LT

• Reduces LT capacity by 50%

protection

PON 1

PON 2

2:N splitter

LT

60

www.alcatel-lucent.comwww.alcatel-lucent.com

61

ConsiderationsA

62

Trends towards next generation PON

GPON enhancements- wavelength blocking filter

- optical parameter monitoring

- midspan extender box

- Class C++ optics

- OTDR integration

WDM-PON- TDM PON per wavelength

- wavelength per customer

- dynamic wavelength switching

- low cost WDM optics

Migration GPON ���� NG-PON on same ODN- capacity increase by wavelength stacking

- coexistence via electrical modulation multiplexing

- 10G coexistence via WDM overlay

time

todaynear future

(5 years from now ?)far future

(10 years from now ??)

63

Status of ongoing standards activities on NG-PON : FSAN / ITU-T

� GPON enhancements

• amendments on wavelength spces : G.984.5 (new)

• optical parameter monitoring : G.984.2 Amnd. 2 (new)

• midspan extender box : G.984.re (draft)

• OTDR integration : input from ALU planned for 2H2008

� White Paper on NG-PON migration: due mid 2009

• NGN1: coexistence scenarios

• NGN2: disruptive approaches

� Physical layer specs of pure 10G solution are expected to be similar

to 10G-EPON PHY specs (wavelength, ODN loss budget, Tx power, Rx sensitivity)

64

PON EvolutionB

65

Pushing the envelope of PON now

Moving up Capacity, Reach & Split

GPON C+

GPONmid-spanextender

GPONB+

XG-PON 1,2DS: 10G

US: 2.5, 5, 10G

WDM overlay in enhancement band

NGA 1

GPON

DWDMOFDM, CDM

NGA 2

Capacity

2010

>2010Lab today

2011-2012Demo Oct 09

� Coexistence� Preservation of OSP (power splitters)

Will likely require change in OSP

66

Readiness for Next Generation PON:

It is all about Capacity, Reach & Split

Less dense areas addressed and central office consolidation

10

Gb/s

2.5

Gb/s

Reach 20km 30 km 60 km

Split 32 64 128

GPON B+Today

GPON C+2009

Extended GPON2009

10 Gb/s PON2010-2011

Extended 10 Gb/s PON1

2 3

� More

bandwidth

for FTTB

and

backhaul

� Increased

split ratio

� More

bandwidth

and

symmetry

per

subscriber

RE

RE

6767 | Presentation Title | Month 2008

Upgrade for 10G GPON Wavelength overlay in both uplink and downlink

GPON

10 Gb/sGPON

No changes to OSP, including

fiber and splitter

10 Gb/s ondifferent wavelengths

(up and down)

WDM to split GPON from

10 Gb/s GPON

1260

-1280

1290

-13301480

-1500

1550

-1560

1575

-1580λλλλ

(in nm)

GPON up GPON downXGPON up XGPON downCATV

GPON

10 Gb/sGPON

68

G.984.5 overviewC

69

ITU-T G.984.5 for co-existence of future PON technologies

� Purpose: define wavelength ranges for additional service signal to be

overlaid via WDM

� Reserved bands are referred to as the “enhancement band” (EB)

� Applications for the EB include video and NGA services

� Wavelengths in the EB may be used for downstream as well as upstream

services

1260 13601340132013001280

UP

14601440142014001380

Reserved

15201480 1500 1540 1560

DOWN

Basic band

1580(1625)

Enhancement band(option 1-1: 1415-1450 nm– non-low-waterpeak fibers)(option 1-2: 1400-1450 nm

– low-waterpeak fibers)

Enhancement band(option 2: 1530-1580 or 1625 nm

(option 3: 1550-1560 nm– video distribution)

Guard band for US Guard band for DS Guard band for DS

70

ITU-T G.984.5 for co-existence of future PON technologies

� Wavelength Blocking Filter (WBF) for ONT to minimize effect of interference

signals from NGA wavelengths

� WBF is used to obtain the required isolation outside of the guard band

� G.984.5 specifies the “X/S” tolerance mask, where X= optical power of interference signal at ONT

I/f and S= optical power of Basic Band signal

λ3 λ6

14601440 15201480 1500 1540

Basic Band

Guard band for DS Guard band for DS

14601440 15201480 1500 1540

Basic Band

X/S (dB)

y2

y1

λ4’

λ4

Λ5’

λ5

71

ITU-T G.984.5: reference diagram

Splitter

WDM1 GPON/NGA GPON/(Video) coupler

GPON OLT

Video-OLT

NGA ONT

…

NGA OLT

GPON ONT(could be replaced by 3:N splitter)

TX

WDM(NGA)

RX

TX

WDM(NGA)

RXWBF

TX

WDM(NGA)

RXWBF

RX-VWBF-V

(NGA) ONT

(NGA) ONT + RF video

TX = Optical TransmitterRX = Optical ReceiverV-RX – Video ReceiverWBF-V = WBF for blocking the inter-ference to V-RXWDM (NGA) = WDM filter in ONT/OLT to combine/isolate wavelengths of (NGA) GPON upstream/downstream (and isolate video signal)WDM1 = WDM filter (in CO) to combine/isolate the wavelengths of (NGA) GPON (and combine the video signals)