Passive Optical Networks - TELECOMMUNICATION NETWORKS GROUP

Passive OpticalNetworks

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sContents

• Optical Access Networks– Passive Optical Networks (PON)

• TDM-PON– Physical Layer and Devices– Traffic Distribution/Scheduling– Power Budget– Standards

• APON/BPON• EPON• GPON

• WDM-PONs– Proposed solutions

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sThe Broadband Connected Household

Energy

monitoring

Video- Conference

Alarm

Lock

Laundry

booking

Real Estate services

Ethernet

HDTVHome station

Set Top Box

100 Mb/sO/E IP

TV

Computers

Telephone

InteractiveGaming

2x20 Mb/s

TV-channels + VoD services

Triple Play

10-50 Mb/s

2x5 Mb/s

DVR

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s

• Both WR and B&S networks are technologies for the backbone and transport network (where large capacity flows exist)

• In the “last mile”, user flows are of smaller bit rates, with high burstiness. There is the need for specific access network technologies

Access Network

Hub

Remote node

Remote node

...NIU

NIU

NIU

NIU = Network Interface Unit

...

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Technologies for access network:• Plain Old Telephone Service (POTS)• Asymmetric Digital Subscriber Loop (ADSL)• Cable-modems using Cable-TV (CATV)

infrastructures • Power Line Communication – PLC• Wireless access technologies

– Local Multipoint Distribution Service (LMDS)– WiFi/WiMax– Cellular networks

• Optical access networks

Access Network

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sxDSL Solutions

• Largely deployed nowadays– Use of existing copper lines– Smooth migration/upgrade of current network

• Bandwidth and reach are limited!

1 Km 2 Km 3 Km 4 Km 5 Km 6 Km Length, Km

8

24

ADSL

ADSL2+

VDSL

52

Data Rate, Mbps

ADSL2

12

Shannon’s information theorem…(S/N-limited, here: crosstalk)

Source: Ericsson

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sADSL: User Devices

• Splitter– separates data from

voice signals

• Modem– (de)modudulates

signals at proper frequencies (e.g., in ADSL, from 25 KHz in upstream, and from 240 KHz in downstream)

Voice Data

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• CATV infrastructures are also called Hybrid Fiber Coax (HFC)

• They offer a unidirectional high speed downstream channel

HFC access network

Head end

Remote nodefiber

coax

amplifiers

tap

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sFiber To The X (FTTx)

FTTC : Fiber To The CurbFTTCab: Fiber To The Cabinet

FTTH : Fiber To The HomeFTTB : Fiber To The Building

“Soon”

Service Node

ONU

FTTH

FTTB

FTTC

FTTCab

Optical Fiber

PON xDSL

OLTONU NT

NT

Internet

Leased Line

Frame/Cell

Relay

Telephone

Interactive

Video

Twisted Pair

ONT

ONT

$$$

“Soon”

“Later”

“Later”

$

$$

$-$$

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sOptical Access Networks

• Low Attenuation, large distances

• Low power consumption• Large Bandwidth, many

broadband users

• Requires new fiber installation

• Outside plant costs are important!!

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• Point-to-Point links– Simple, standardized and mature technology– N fibers lines– 2N transceivers

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• Active Optical Network– Simple, standardized and mature technology– 1 fiber line– Curb Switch →

power in the field

– 2N+2 transcievers

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• Passive Optical Network (PON)– Simple, under standardization technology– 1 fiber line– N+1 transceivers– passive devices (splitters)

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s

Passive Devices

Downstrea

m Traffic

Upstream Traffic

ODN

PON Overview

OLT: Optical Line TerminatorONU: Optical Network UnitODN: Optical Distribution Network

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sTime 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

TDMA Time Division Multiple Access

WDMA Wavelength Division Multiple Access

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sPON Evolution

• TDM-PONs– Standarized– 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, …


TDM-PONs

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OLT

PON Physical Layer

PassiveSplitter

ONU

ONU

ONUODN

• Passive splitter/combiner(s)• Two separated channels

– Downstream (OLT → ONUs)

– Upstream (ONUs → OLT)

• A 3rd channel can be used for broadcasting video

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sOptical 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

ATTE

NU

ATIO

N (

dB

/km

)

WAVELENGTH (nm)

1310nm

1550nm

850nm

STD SMFZWP SMF

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sOptical Fiber: Chromatic Dispersion

• Causes signal pulse broadening

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sWavelengths

1310nmLow loss (∼0.5 dB/km)Zero chromatic dispersion

1490nm1550nm

Low loss (∼0.3 dB/km)Chromatic dispersion (∼10-17 ps/nm.km)Optically amplified by EDFAs (1550nm)

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sLasers 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

+

- λ

mirror

gain

AR coating

+

- λ

DFB

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sPhotodiodes (PD)

• PIN Photodiodes – Good optical sensitivity (∼-22 dBm)– Silicon for shorter λ’s (eg 850nm)– InGaAs for longer λ’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

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sTypical PON Configuration

• Wavelengths

• Transceivers

Dual Fiber 1310nm.

Single FiberUpstream on 1310nmDownstream on 1490nm

Upstream Downstream

ONU FP PIN

OLT APD DFB

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sDownstream Traffic

• Downstream traffic is broadcasted to all ONUs– Weak security

• ONUs filter data (frames) by destination address

OLTPassiveSplitter

ONU

ONU

ONU

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sDownstream Traffic Scheduling

• OLT schedules traffic inside timeslots– Time Division Multiplexing (TDM) scheme

• Time slots can vary from ∼μs to ∼ms

OLTPassiveSplitter

C

A

A B C B

B

AB

CB

A B C B

AB

CB

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sDownstream Frame Reception

• Each ONU receives all the frames with the same constant power– Simple receiver (low-cost) @ ONUs

• Frames have preambles/markers

OLT

C

B

A

1 km

3 km

7 km

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sUpstream Traffic

• All ONUs share the same upstream channel– ONUs cannot exchange data directly– Collisions may occur at the splitter/combiner

OLTPassiveSplitter

ONU

ONU

ONU

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sUpstream Traffic Scheduling 1/4

• Media access mechanisms– Contention-based (similar to CSMA/CD)

• ONUs cannot detect collisions due to directional properties of optical splitter/combiner

– Guaranteed (TDMA, OCDMA, etc.)

OLTPassiveSplitter

C

A

B

A

B B

C

AB

CB

Collision!!

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• In general, PON standards propose Time Division Multiplexing Access (TDMA) schemes– Upstream time slicing and assignment

OLTPassiveSplitter

C

A

A B C B

B

A

B B

C

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• Typically, downstream traffic carries grants that schedule upstream traffic

• Grant distribution must take into account the different propagation times to reach each ONU

OLTPassiveSplitter

C

A

BA B C B

2 1 AB

CB

A B C B

AB

CB

2

1

2

1

2 1

10 km

2 km

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• PON standards define ranging mechanisms– the method of measuring the logical distance between each

ONU and the OLT and determining the transmission timing such that upstream cells sent from different ONUs do not collide

2

1

OLTPassiveSplitter

C

A

AC

B

A

C

C

10 km

2 km

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sUpstream Frame Reception

• The OLT receives frames with different powers– Much difficult to recover synchronism– Burst Mode Receiver (complex) @ OLT

• Sets 0-1 threshold on a burst basis

OLTPassiveSplitter

C

B

A

1 km

3 km

7 km

A

BB A

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sPower Budget

• Maximum optical power loss in the ODN– Difference between the TX power and the

sensitivity of the RX

• Considers attenuation of fiber, connectors, splices, splitters, etc.

ODN Loss Model Assumptions

Connection

Conventional Low-loss

0.75 dB 0.15 dB

Splices 0.088 dB 0.067 dB

Fiber (1310nm) 0.5 dB/km 0.4 dB/km

Fiber (1490/1550nm) 0.3 dB/km 0.2 dB/km

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sPassive Splitters

• 1x2 Splitter • 1xN Splitter

• Every time the signal is split two ways, the signal is reduced by 10log(0.5)=3dB• Loss ∼3dB × log2 (#ONUs)

Conventional Low-loss

Splitter 1x2 3.7dB 3.4dB

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sSplitter/Couplers Configurations

4-stage 8x8 3-stage 8x8

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• Upstream (@1310nm) Power Budget = 30 dB• Downstream (@1490nm) Power Budget = 22 dB

Transceiver Assumptions

TX Power RX Sensitivity

ONU (FP+PIN) 0 dBm -22 dBm

OLT (DFB+APD) 1 dBm -30 dBm

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sVideo Distribution over PONs

• Video can be distributed in several ways

• RF video signal (overlay video)– Uses the same technology employed in cable TV

networks– Requires a dedicated wavelength and high-power– Supports both analog and digital channels

• IP video signal (integrated video)– Uses IP protocol to delivery video services– Can use the same wavelength as data and voice– Video head end can be shared among many

networks/platforms

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OLT

RF Video Signal

PassiveSplitter

ONU

ONU

ONU

• A 3rd channel (1550nm) can be used for video• A high-power signal is required for video

– The video signal is amplified by an EDFA at the OLT

EDFA

video

video

video

video

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sRF Video Issue: Brillouin Scattering

• All optical fibers have a physical limitation known as stimulated Brillouin scattering (SBS)

• SBS occurs when a high power optical signal over relatively long length (>8km) fiber generates variations in the fiber’s optical properties and scatters optical signals in the reverse direction.

• As power levels increase, so does the effect, resulting in transmitter signal loss and noticeable video signal degradation on a subscriber’s TV

• In general, this results in a power budget of ∼21 dB (@1310nm)

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sConventional ODN Analysis

Coonventional ODN

0.0

20.0

40.0

60.0

80.0

100.0

1 2 4 8 16 32 64 128

Number of ONUs (split)

Max

imum

ONU

Dis

tanc

e [k

m]

Upstream Downstream RF Video

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sLow Loss ODN Analysis

Low loss ODN

0.020.040.060.080.0

100.0120.0140.0

1 2 4 8 16 32 64 128

Number of ONUs (split)

Max

imum

ONU

Dis

tanc

e [k

m]

Upstream Downstream RF Video

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sReach/Split Ratio Improvement

• Use of Forward Error Correction (FEC) techniques

• ITU-T G.795– Reed Solomon Code– Low frame processing delay (∼12μs)– ∼

6% overhead

– Up to ∼5.5dB gain• APD ∼

electrical gain (limited by shot noise)• PIN ∼

½ electrical gain (limited by thermal noise)

• Improvements– Increase 1:32 split @ 10km– Allow 1:16 split @ 20km

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sSummary

• TDM-PONs have limited reach/split performance

• Standards define– Physical Layer– Downstream and Upstream Frame Formats– Upstream Grant Distribution Mechanism

• Ranging Mechanism


PON Standardization

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sPON Standards

Full Service Access Network (FSAN)

Group

Ethernet in the First Mile (EFM)

Alliance

International Telecommunication

Union (ITU-T)

Institute of Electrical & Electronics

Engineers (IEEE)

APON/BPON (G.983)

EPON (802.3ah)

GPON (G.984)

Propose standards

Ratify standards

Working Groups

StandardsBodies

Standards20042003

1998/2001

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sFSAN Members: Service Providers

FSAN Recommends Standards to the International Telecommunications Union (ITU)

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sEFM Alliance: Equipment Vendors

• Members– AllOptic, Cisco, Elastic Networks, Ericsson,

Extreme Networks, Infineon, Intel, NTT, Passave, Texas Instruments, …

• Position Ethernet in the First Mile as a key networking technology for the access network

• Support the Ethernet in the First Mile standards effort conducted in the IEEE P802.3ah Task Force

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sTechnical Standards Comparison

BPON EPON GPONStandard ITU G.983 IEEE802ah ITU G.984

Data Packet Cell Size 53 bytes 1518 bytes 53 to 1518 bytes

Maximum Speed Configurable1.2 Gb/s downstream;622 Mb/s upstream

Symmetric 1.25 Gb/s Configurable2.4 Gbps downstream2.4 Gbps upstream

Traffic Modes ATM Ethernet ATM, Ethernet or TDM

Voice ATM VoIP ATM, VoIP or TDM

Video 1550 nm overlay (RF) Either over RF or IP

ODN Power Budgets 20-30 dB 21-26 -dB 20-30 dB

Max PON Splits 32 16 or more 64

Reach 10-20 km 10-20 km 20 km


APON

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sATM PONs (APONs)

• The first PON standard was based on ATM cells• It consists of:

– Downstream Channel @ 155 Mbps or 622 Mbps– Upstream Channel @ 155 Mbps

• It supported different services:– Digital Broadband Video (No Analog Video)– Multimedia Services– ATM Services

• Those were the ATM days!

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sAPON Physical Parameters

Fiber Type G.652 (STD SMF)

Power BudgetClass B: 10-25 dBClass C: 15-30 dB

Max Reach 20 km

Split Ratio 16 or 32

TransmissionSingle FiberDual Fiber

Single Fiber Dual Fiber

Upstream 1310 nm 1310 nm

Downstream 1550 nm 1310 nm

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sAPON Architecture (Single Fiber)

Downstream 1550 nm

Upstream 1310 nm

Voice, Video & Data

Optical Splitter

1x32 Or Cascade

Optical Coupler

Voice, Video and Data Voice, Video and Data

1310 nm 1550 nmDownstreamUpstream

Voice and Data Voice and Data

OLT

Video (l)

Data (AAL5)

POTS (AAL1,2)

ONU

100 nm 100 nm

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sDownstream Frame Structure

• Based on STM-1 (155 Mbps) line rate• Each frame (∼150 μs) carries timeslots of 53B

– The frame is long – 56 slots (155 Mbps) → ∼3.6 μs timeslots– 224 slots (622Mbps) → ∼0.9 μs timeslots

• Each timeslot contains – a data cell (ATM)– or a Physical Layer Operation & Management cell

(PLOAM)– Every 28 slots a PLOAM cell is inserted.

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sDownstream PLOAM cell

• Downstream PLOAM cells are responsible for– allocating bandwidth (via grant fields), – frame synchronization, – error control,– ranging, – and maintenance.

• Payload of 48 bytes– Carries 27 grants– Each grant, schedules1 upstream ATM cell

Downstream

PLOAM Cell

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sDownstream ATM cell

• ONUs filter downstream ATM cells and receive only those that are addressed to them

• Each ATM cell has a 12-bit addressing field associated with a virtual circuit– At most 4096 ATM circuits are allowed per PON

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sUpstream Frame Structure

• Each frame (∼150 μs) carries 53 slots of 56 bytes– 53 bytes of ATM or PLOAM cell– 3 overhead bytes per ATM cell

• The 3 overhead bytes contain – at least 4 bits of guard time

• to prevent collisions with cells from other ONUs.

– a preamble field for bit synchronization and amplitude recovery.

– a delimiter field is used to indicate the start of an incoming cell.

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sUpstream PLOAM cell

• Upstream PLOAM cells carry– alarms, – alerts – ranging messages– receiver and

transmitter status

• Upstream PLOAM rate– Defined by the OLT for

each ONU– Minimum is 1 PLOAM

every 100 msUpstream PLOAM Cell

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sUpstream Traffic Scheduling

• Coupled downstream and upstream timing– Both frames have equal length (∼150 μs) – Synchronization is based on downstream frames

• The OLT, by means of the ranging process, aligns all ONUs upstream frames to an unique downstream frame

• The downstream frame carries grants for ONUs to allow upstream transmission

• One grant = One cell– Data Grant– PLOAM Grant– Divide_Slot Grant– …

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sUpstream Minislots

• An upstream slot can contain a divided_slot• The divided_slot fits into one upstream slot and contains a

number of minislots coming from a set of ONUs• The OLT assigns one divided_slot grant to this set of ONUs

for sending their minislots• Minislots are used to report status information of the ONUs

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sRanging Process

• The OLT must compute the RTT for each ONU, and sends an equalization delay time to each of them– PLOAM cells are used for this purpose

• ONUs implement the equalization delay to emulate an equidistant network

OLTPassiveSplitter

ONU

ONU

ONU

20 km

20 km

20 km

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sAPON Ranging

• OLT sends a Ranging Grant and waits for the ONU response

• Once, the OLT has received all responses, it calculates the equalization delays and communicates this information to the ONUs, who adjust their transmission

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sAPON Bandwidth Allocation

• Downstream Bandwidth– bandwidth can be dynamically allocated by the

OLT based on the ONU’s services

• Upstream Bandwidth– bandwidth is allocated statically through grants– minislots mechanism for reporting ONUs’ queues,

but no dynamic bandwidth allocation sheme defined

– No dynamic bandwidth allocation!


BPON

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sBroadband PONs (BPONs)

• BPONs are similar to APONs, but add extra functionalities

• Include APONs (G.983.1)• Defined in the ITU-T G.983.3 (2001)• Support higher rates

– Downstream (155, 622 & 1244 Mbps)– Upstream (155 & 622 Mbps)

• Defines– alternative wavelength plan including additional

wavelength band • for downstream video broadcast,

– dynamic upstream bandwidth allocation (G.983.4)– protection mechanisms

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sBPON Physical Parameters

Fiber Type G.652 (STD SMF)

Power BudgetClass A: 5 - 20 dBClass B: 10-25 dBClass C: 15-30 dB

Max Reach 20 km

Split Ratio 16 or 32

Transmission Single Fiber

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sBPON Wavelength Allocation

APON

BPON

Water Peak

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sBPON Architecture

Downstream 1490 nm

Upstream 1310 nm

Voice & Data

Optical Splitter

1x32 Or Cascade

Optical Coupler

Video 1550 nm

Voice and Data Voice and Data VideoVideo

1310 nm 1490 nmDownstreamUpstream

1550 nm

Digital TVAnalog TV HD/VOD550 MHz 860 MHz42 MHz

Voice and Data Voice and Data

EDFA

OLT

Video (l)

Data (AAL5)

POTS (AAL1,2)

ONU

100 nm 20 nm 10 nm

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sFrames

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sDynamic Bandwidth Allocation (DBA)

• DBA is the process by which ONUs dynamically request upstream bandwidth, and the method the OLT reassign bandwidth accordingly

• BPONs defines two DBA schemes– buffer status reporting (SR)– idle cell monitoring, or no status reporting (NSR)

OLT

ONU-A

ONU-B

ONU-C

ONU-D

Dynamic allocationof bandwidth

Shared bandwidth

Dedicated bandwidth

GRANTS

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sTransmission Containers (T-CONTs)

• Entity used for upstream bandwidth allocation– Responsible for requesting and receiving grants– Associated to a buffer and report its status

• A single T-CONT can carry ATM traffic with various service classes and virtual circuits

• A data grant/request is associated with one T-CONT• T-CONTs are essentially “pipes” that carry ATM circuits

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sNo Status Reporting (NSR)

• OLT inspects each incoming cell from a specific T-CONT in a predefined time frame– Remembers the ATM connections that are associated with a

specific T-CONT

• For example, the OLT calculates the utilization rate of the currently assigned bandwidth by monitoring the number of effective received cells from specific T-CONTs, and uses this value as the bandwidth request information– The bandwidth allocation reserved for a T-CONT is

INCREASED if the current allocation is largely utilized and DECREASED otherwise

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sStatus Reporting (SR) 1/3

• SR-ONUs explicitly report to its OLT PON interface• Since a number of ONUs and their T-CONTs may report

queue lengths of T-CONT buffers, it is imperative to balance the amount of information with the upstream bandwidth consumption of these reports

• Generally the OLT will generate divided_slot grants to request a queue length for the specified ONU according to the service requirements

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• When an ONU recognizes a divided_slot grant, the ONU can transfer information in a minislot in the divided_slot

• This minislot contains the queue length for every T-CONT using non-linear coding and CRC-8

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• SR-ONUs shall report the queue length of their T-CONTs when requested by their OLT

• The queue length is the sum of the total number of cells in all the class buffers that are connected to a T-CONT

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sFault Tolerance

• BPON defines different protection schemes– Based on Automatic Protection Switching (APS)– Duplication of transceivers (TR), splitters and

optical fiber sections

• Similar to metro/core networks

PassiveSplitter

Feeder Section

Drop Section TR

TR

TR

TR

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s

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

OLTONU-1

ONU-2

ONU-n

・・

TR

TR

TR

TRTR

TR

TR

TR

OLT ONU-1

ONU-2

ONU-n

・・


EPON

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s

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

IEEE802.11wirelessMAC 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

IEEE 802.3.ah

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sEthernet PONs (EPONs)

• All data packets carried in EPON are encapsulated in Ethernet frames– Support for variable size packets

• Use of Ethernet frames without modification makes it possible to use existing low-cost Ethernet parts

• Similar wavelength plan to BPON• Maximum bit rate is 1Gbps (1.25 Gbps 8B/10B)• Minimum number of splits is 16• Maximum reach is 10 km or 20km• Different configurations are allowed

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sEPON Configurations

(1) Tree Topology (2) Ring Topology

(3) Tree with Redundant Trunk (4) Bus Topology

OLT

ONU

ONU

ONU

ONU

OLT

ONU

ONU ONU

ONU

OLT

ONU ONU

ONU ONU

OLT

ONU

ONU

ONU

ONU

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sDownstream Traffic

• Similar to a shared medium network • Packets are broadcasted by the OLT and selected

by their destination ONU

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sUpstream Traffic

• ONUs synchronized to a common time reference• Centralized arbitration scheme• OLT grants access to ONU for a timeslot

– Several Ethernet packets

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sIEEE 802 Compliance

• IEEE 802 assumes all stations to be connected to a shared-medium (single access domain)

• Single-station domains connected by point-to- point links form a switched LAN

• Problem: IEEE 802 compliance – ONUs cannot communicate with one another due to

directivity of passive devices

• 1st Solution: Emulate a point-to-point topology– Loss of useful downstream broadcast nature

• 2nd Solution: Emulate a point-to-point topology but with a special broadcast feature

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sLogical Topology Emulation (LTE)

• PON devices implement a logical topology emulation (LTE) function– To preserve the existing Ethernet MAC operation,

LTE must reside below the MAC sublayer

• Emulation relies on tagging Ethernet frames– Logical Link Identification (LLID) – Replaces 2 bytes of 8 of the Ethernet preamble

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sEPON Ethernet Tagging

• Unicast LLID–Established between the OLT and each ONU–Point-to-point links–ONUs filter frames by their assigned LLID

• Universal LLID–Used to define a broadcast service–Received by all ONUs–Exploits downstream broadcast nature of PONs!

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sThe Muti-Point Control Protocol (MPCP)

• Original Ethernet MAC protocol cannot operate properly in the upstream channel (no collision detection)

• MPCP (Multi-Point Control Protocol) – In-band signalling– Messages (64 bytes)

• GATE • REGISTER• REGISTER_REQUEST• REGISTER_ACK• REPORT

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sMPCP Modes of Operation

• Auto Discovery Mode– Detects newly connected ONUs and learns the

round-trip delay and MAC address of that ONU– Messages: GATE, REGISTER, REGISTER_REQUEST,

REGISTER_ACK

• Bandwidth Assignment Mode – Assigns transmission opportunities to registered

ONUs– Messages: GATE, REPORT

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sAuto Discovery Summary

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sBandwidth Assignment Mode

• The OLT sends a GATE message (grant) and schedules upstream transmission for a specific time interval

• ONUs send REPORT messages with their queue status claiming grants

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s“Just-in-Time” Scheduling

• The GATE message is sent so that when the ONU receives the message it starts transmitting– Only time length of access interval is needed

• However, Ethernet frames cannot be preempted so collision may occur

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s“Start Time” Scheduling

• The GATE message carries– a Start Time,– and its length

• Requires a common timereference (16ns granularity)

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sMPCP Clock Synchronization

• Both the OLT and the ONU have 32-bit counters that increment every 16 ns– These counters provide a local timestamp

• MPCP messages contain a timestamp field

• When the ONU receives a MPCP message, it sets its counter according to the value in the timestamp of the received message– Local clock is then “synchronized” with the OLT

one

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sRanging

• When either device transmits a MPCP message, it maps its counter to the timestamp field– Useful for the ranging process

RTT = T2 - T1

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sREPORT Message

• REPORTs are generated at the ONU

• A REPORT message may contain queue reports (DBA)• REPORT messages can be used with timestamps only (Ranging)

• The OLT must – process REPORT messages– consider the REPORT when allocating bandwidth

• REPORTs must be issued periodically


GPON

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sFrom BPON to Gigabit PON (GPON)

• BPON Issues– Shortage of bandwidth in connecting Gigabit

Ethernet – Inefficient allocation of packets due to AAL5– High cost of interface cards due to low penetration

of ATM– Relatively insignificant role played by ATM in the

core network

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sGPON Standardization

ITU-T Outline Adoption

G.984.1G-PON service requirements(General characteristics)

Mar. 2003

G.984.2G-PON Physical Layer spec.(Physical Media Dependent (PMD) layer specification)

Mar. 2003

G.984.3G-PON TC layer spec.(Transmission convergence layer specification)

Feb. 2004

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sGPON Requirements

Item Target

Services and QoSperformance

Full services(10/100/1000Base-T, voice, leased lines etc.)

Bit rates1.25 Gbit/s symmetric or higher (2.4 Gbit/s). Asymmetric with 155/622Mb/s upstream

Physical reach Max. 20 km or max. 10 km

Logical reach Max. 60 km

Branches Max. 64 in physical layer

Wavelength allocation

Downstream: 1480 – 1500nmUpstream: 1260 – 1360nm

Downstream video wavelength (1550 – 1560nm) may be overlaid

ODN classes Class A, B and C (same as requirements for ODN for BPON)

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sG.984.1 Service Requirements

Item Target

Bit rates1.25Gbit/s symmetric or higher (2.4 Gbit/s). Asymmetric with 155/622Mb/s upstream

Physical reach Max. 20 km or max. 10 km

Logical reach Max. 60 km

Branches Max. 64 in physical layer

Wavelength allocation

Downstream: 1480 – 1500nmUpstream: 1260 – 1360nm

Downstream video wavelength (1550 – 1560nm) may be overlaid

ODN classes Class A, B and C (As B-PON, G.982 is applied)

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sG.984.2 Physical Requierements

Item Spec.

Bit rates1.244Gbit/s and 2.488Gbit/s symmetricalAsymmetrical with 155.52/622.04 Mbit/s upstreamError rate: better than 1E-10

Correction of errors due to dispersion

Up to 10km: use of FP without FEC

Up to 20km: use of FP with FEC (FEC is not needed when using DFB)

Optical devices LD + PIN (APD may also be used)

Overhead in upstream signal

4Bytes (155.52Mbit/s), 8Bytes (622.08Mbit/s)12Bytes (1.244Gbit/s), 24Bytes (2.488Gbit/s)

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sG.984.3 Transmission Convergene (TC)

• ATM ATM services are carried by ATM frames• Other services are in principle carried by Generic frames• A mix of the two types of frame can be configured

ATM service Other services

Layer 2

Layer 3

Layer 4

Layer 5or higher

Layer 1

ATM frame

PON-PHY

TCP+UDP etc.

IP

Ethernet

Generic frame

T1/E1TDM

POTS VideoData

VoIP

G.983 base G.707 base

ATM

GPON TC (GTC) frame

AAL

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sMultiplexing Mechanisms

• T-CONT entity (as BPON): associated to ports and/or VP/VC

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sGPON Encapsulation Mode (GEM)

• GEM provides a Generic Frame where to carry both TDM and packet traffic over fixed data-rate channels– Similar Generic Framing Procedure (GFP) used in

SDH/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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sMapping Modes

• Framed– Optimized for bandwidth efficiency at the expense

of latency– It encapsulates complete Ethernet (or other types

of) frames with a GEM header

• Transparent– Used for low latency transport of block-coded

client signals such as GbE, Fibre Channel, ESCON, FiCON, and Digital Video Broadcast (DVB)

– Small groups of 8B/10B symbols are transmitted rather than waiting for a complete frame of data

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sGPON-TC (GTC) Frames

• Fixed frame duration (125us)• Transports both ATM cells and GEM Frames• Used in both downstream (DS) & upstream (US)

– Use of Pointers to allocate upstream bandwidth

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sUpstream Scheduling

• Downstream frames indicate permitted locations for upstream traffic– Use of pointers (byte units)

• Minimum bandwidth allocation 64Kbps (1 byte @ 125us)

– Upstream frames synchronized with downstream ones

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sDownstream Frame Structure 1/3

• It consists of– a Physical Control Block Downstream (PCBD)– the ATM partition (N×53 bytes)– the GEM partition

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• The PBCD carries basically– Synchronization fields (used by ONUs)– Upstream Bandwidth grants (upstream access)

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• Each Access grants is composed of– an AllocId associated with the T-CONT– a Start Time and Stop Time expressed in bytes that indicate

when to access the usptream channel and when to release it

• As in BPONs, upstream access is effectively done delaying access for a specific equalization delay

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sDownstream Frame Structure

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sUpstream Frame Structure 1/3

• Each frame contains transmissions from one or more ONUs

• Four types of overheaders are present

– Physical Layer

– PLOAM

– Power Leveling

– Dynamic Bandwidth Report

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• A preamble and a delimiter are attached to each burst in order to recover the frame at the OLT

• Their values are absolute in time and variables in bits

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sUpstream Burst Lock-In Time

• BPON: stringent lock-in 3 bytes per cell timing

• GPON: more relaxed timing– 622 Mbps upstream: 8 bytes– 1.2 Gbps upstream: 12 bytes– 2.4 Gbps upstream: 24 bytes

• Results:– BPON = stringent timing = more expensive

components– GPON = more relaxed timing = cheaper

components– GPON = lowest cost path for higher bandwidth

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• The usptream frame payload can be used to carry– ATM cells,– GEM frames– or DBA reports

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sDBA Reports


TDM-PON Summary

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sPON Technical Summary

Type of PONBPONBroadband-PON

GPONGigabit-PON

EPONGigabit Ether-PON

StandardizationFSAN / ITU-TG.983 series

FSAN/ITU-TG.984 series

EFM/IEEE

Transmission frame

ATMGEM(partly ATM)

Ethernet

Transmission speed(bit/s)

156M, 622M, 1.2G (downstream)

1.2G, 2.4G, 156M (upstream), 622M (upstream)

1.25G(1G after decoding)

Wavelength (μm) 1.3/1.5

Wavelength multiplexing of

videoPossible

Upstream bandwidth control

TDMA coupled to Downstream Decoupled TDMA

Services provided ATMFull services

(phone, IP, TDM)IP-based services

Year of introduction 2001 2003 2004

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sPON Reach/Split Comparison

10 20Applicable distance (km)

0

10

20

30

Nu

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of

splits

EPONClass PX20

G(B)PONClass B

G(B)PON Class C

Assumptions for calculation・Optical splitter insertion loss

32-way split: 17dB16-way split: 14dB8-way split: 11dB4-way split: 8dB

・Fixed loss (conn., etc.): 4dB・Line loss:0.5dB/km

G(B)PON：Class AEPON：Class PX10 (note)

Difference between sending and receiving levels・G(B)PON

Class A: 5-20dBClass B: 10-25dBClass C: 15-30dB

・EPONClass PX10: 5-20dBClass PX20: 10-24dB

Note: Since Class PX10 assumes the use of FP-LD, its applicable distance is max. 10 km due to effects of mode dispersion. DFB-LD is used in other Classes.

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sPON Transmission Efficiency

0

200

400

600

800

1000

1200

1400

EPON GPON BPON

Mb/

sscheduling OH : framedelineationscheduling OH : PHY burst OH

scheduling OH : controlmessagespayload encapulation OH

line coding

payload

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sPON 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/GPON


WDM-PONs

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sFiber

• 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

ATTE

NU

ATIO

N (

dB

/km

)

WAVELENGTH (nm)

1310nm

1550nm

850nm

STD SMFZWP SMF

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sCoarse WDM (CWDM)

• Upto 18 channels (1271-1611nm, 20 nm spacing)• Cheap transmitters (no strict tuning, thus, no thermal

control needed)• Reach limited by the lowest wavelength

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sArrayed Waveguide Gratings (AWG)

• AWG has already been used in many long-haul WDM systems– mulitplexer/demultiplexers– add/drop multiplexer

• AWGs route each specific ingress wavelength to a unique output port

• AWG insertion loss is 4-5dB regardless of the number of channels– Thus, larger distances can be reached

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sWDM Techniques in PONs

• WPON: Broadcast and select PONs• WRPON: wavelength routed PONs

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sSimple WDM-PON

• Number of ONUs limited by wavelengths• Point-to-point topology• Long-reach (almost point-to-point reach)

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sComposite-PON (CPON)

• Downstream uses AWG (improves reach)• Upstream uses combiner

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sLARNET

• Downstream AWG routes wavelengths (reach)• Upstream AWG separates wavelengths (low cost

1310nm LD) and improves bandwidth

Wideband upstream signals are “sliced” by the AWG

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sRITENET

• Upstream transmitters in ONUs modulate a downstream-broadcatsed unmodulated carrier (no need of light sources at ONUs)

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sMultistage-PON

• AWG size is limited by fabrication technology limits →

multiple stages of AWGs

• Wavelengths are routedin groups at the 1st stage and individually at the 2nd

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sSuper-PON

• Extends reach (∼100km) and split ratio (∼2000)– Uses optical amplifiers on the feeder– Uses several wavelengths (DWDM)

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sSUCCESS-DWA PON

• Offers dynamic wavelength allocation (DWA) by adding tunable lasers at the OLT

OLT

ONUs

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