On The Next-GenerationOptical Access Architecture

Joseph KimAST, STMicroelectronics

Washington University in St. Louis

Dec. 3, 2004

Outline

I. ST and SNRC Introduction

II. Paradigm Shift in Optical Networking

III. Next-Generation Optical Access Architecture• Why Optical Access?

• TDM-PON: Current-Generation Optical Access

• Stanford University aCCESS (SUCCESS)

IV. Summary

I. ST and SNRC Introduction

Overview of STMicroelectronics

Overview of Stanford Networking ResearchCenter

Advanced System Technology

Mission

• To provide the advanced system

knowledge able to establish ST as thesystem on a chip leading company in themarket for the products of the next decade

Role

• To provide the Company with long-term corebusiness and leadership in key markets

SAN JOSE’

SAN DIEGOCATANIA GRENOBLE

GENEVA

MILANO

AIX EN PROVENCE

BOSTON LECCE

HONG KONG

= large research lab

(>15 people)

NOIDA

BANGALORE

BRISTOL LUGANO

PORTLAND PARIS

AST - Global R&D Organization

AST - Optical Networking Activities

GIANT

Validation of GPON indemonstrator

Integration of building blocks

Performance (efficiency, QoS)testing

Service demonstration

GBRA

GXT0

CPA

GLTA Board GNTA Board

GBLALD+

AFE

PD+

AFE

WD

M

GXTP

NT version

PD+

AFE

LD+

AFE

WD

M CDR

GXTP

LT

version

LD

Driver

ARM

Designed

by STMDesigned

by STM

Designed

by Intec

Designed

by IntecSystem Info control

PTSP OBC PTSP OBC

Designed

by ABellDesigned

by ABell

1.25 Gbps

622 MbpsGBRA

GXT0

CPA

GLTA Board GNTA Board

GBLALD+

AFE

PD+

AFE

WD

M

GXTP

NT version

PD+

AFE

LD+

AFE

WD

M CDR

GXTP

LT

version

LD

Driver

ARM

Designed

by STMDesigned

by STM

Designed

by Intec

Designed

by IntecSystem Info control

PTSP OBC PTSP OBC

Designed

by ABellDesigned

by ABell

1.25 Gbps

622 Mbps

SYMPHATI

Symmetrical PON at high bit rate

Specify and design chipset for 1.25Gbps upstream GPON - Class B

Lab demo at 622 Mb/s upstreamAPON system

MEMS – free space

Bubble switch

ST Competences in Optics - 1

ST Competences in Optics – 2

Stanford Networking Research Center- Overview

Established in 2000• 5 Founding Members (ST,

3com, Bosch, Cisco, Sony)

• 5 Senior Members

• 13 Affiliates

3 Major Research Areas• Wireless Access

• Internet Technologies

• Information Services

6 Projects• ~ 20 faculty

• ~ 40 PhD students

Annual Budget• $3.5M/year

For more information• http://snrc.stanford.edu

SNRC - Current Projects (2003~2005)

Next Generation

Access Networks*

Robust & Adaptive Protocol Design

for Multimedia Wireless Networks

SupraNodes: Next Generation

Switching Network Elements

Novel Design, Analysis and

Monitoring Methods

for High-speed Networks

Collaborative Networks of

Imaging Sensors

Separating Syntax, Semantics, &

Patterns

in Web Service Composition

Optical Networking Area

SNRC - Opportunities

Ideal venue for collaborations

• Between Industry and Faculties/Students

• Between Industries

• Between Faculties/Students

Through

• Funded multi-PI research projects

• Fellow/Mentor/Advisor programs

• Researchers-in-Residence (R-i-Rs)

PNRL - Overview

Founded in 1990 and Headed by:

Professor Leonid G. Kazovsky

Group Members:

8 Ph.D. students,

2 visiting scholars,

1 Researcher-in-Residence,

1 consulting professor.

Equipment: ~ $5,000,000

Home Page: http://pnrl.stanford.edu

PNRL - Current Access Projects

Next-Generation Optical Access

-ST(@SNRC) with F/M/A

Advanced Access Networks Research

- KDDI, Japan

Next-Generation Burst-Mode Receiver

- ITRI, Taiwan

II. Paradigm Shift in Optical Networking

Overview

Traditional Way of Using Wavelengths

New Way of Using Wavelengths

Continuous-Mode vs. Burst-ModeCommunications

Examples

Enabling Technologies

Paradigm Shift in Optical Networking

Towards more Flexible, Dynamically-Reconfigurable

Optical Networks from Fixed, Static ones

Driving forces behind this shift• Mismatch between service/usage model & network infrastructure

• Unbalance between backbone (waste of BW) and access (lack ofit)

• Rapid development in enabling technologies

! Tunable optical components

! Burst-mode communications

! Optical packet/burst/flow switching

Dynamically-reconfigurable networksbetter meet varying user demands even

with fewer resources!

Traditional Way of Using Wavelengths

TX

TX

TX

TX

RX

RX

RX

RX

SW SW

Optical Network withPassive/Semi-passive Nodes

New Way of Using Wavelengths

TunableTX

SW

TunableTX

SW

TunableTX

SW

FixedRX

SW

FixedRX

SW

FixedRX

SW

Continuous-Mode vs. Burst-ModeCommunications

TX RXSW SW...010110100101110100101001001010101111101001010101…

SONET/SDH

Packet Packet Packet

RX SW10011…0110

Packet Packet Packet

011…010 011…010

Examples

WAN• TWIN, Lucent Bell Labs

MAN• HORNET, PNRL/Stanford

• RINGO, Politechnico de Turin

Regional Access• ONRAMP, Lincoln Lab/MIT

Access• STARNET, DWA-PON & SUCCESS, PNRL/Stanford

• TOBASCO, Lucent

TWIN*: Network is a Giant Switch

TWIN cloud

DS-3interface

Ethernetinterface

ATMover OC-3interface

Traffic destined to this nodeshould use purple wavelength

Network ~ Logical node

Core ~ Virtual back-plane

Edge node ~ Port

* Indra Widjaja et al., “Light core and intelligent edge for a flexible, thin-layered, and cost-effective optical

transport network,” IEEE Comm. Mag., vol. 41, no. 5, pp. 30 - 36, May 2003.

Tunable

Transmitter

!1

POPAccess Point

Access Point

Access Point

Access Point

Access Point. . . . . .Wireless

IP Cell!"

Packet

Switch

Local

network

POP = Point of Presence

To long-haul network

!1

dropMAC

Packet

Receiver

HORNET*: Flexible, Multi Service Ring

* Ian White et al., "A summary of the HORNET project: A next-generation metropolitan

area network", IEEE JSAC, vol. 21, no. 9, pp. 1478-1494, Nov. 2003.

* N. M. Froberg, "The NGI ONRAMP Test Bed: Reconfigurable WDM Technology for Next

Generation Regional Access Networks," IEEE JLT, Dec. 1998. (Slide from Sarah Dubner)

ONRAMP*: Regional Access

DWA-PON*

* Y-L. Hsueh et al., “Success-DWA: A highly scalable and cost-effective optical access network”,

IEEE Comm. Mag., vol. 42, no. 8, pp. 24 - 30, Aug. 2004.

TL1

TL2

TL3

TL4

User 1

User16

…

User17

User32

User33

User48

User49

User64

AWG

Ch 1

Ch16

Ch 1

Ch16

Ch 1

Ch16

Ch 1

Ch16

……

…

……

……

PON1

PON2

PON3

PON4

_

…

User Channel 1 User Channel 2 User Channel 16

AWG Channels

1 2 3 4 5 6 7 8 6

16

2

6

3

6

4

TL: Tunable Laser

Enabling Technologies

Common denominator in technologies enablingflexible, dynamically-reconfigurable opticalnetworks

• CWDM

• Tunable Filters

• Tunable Lasers

• Burst-Mode Receivers (BMRs)

The paradigm shift pushes these technologies

towards the edge of the networks!

Coarse Wavelength Division Multiplexing

ITU-T Recommendation G.694.2• 1270-1610 nm, 18 wavelengths, 13nm flat-top

• Permitting low-cost components

! Uncooled, unstabilized, direct-modulated transmitter

Migration path: CWDM to DWDM• Iannone, “In-Service Upgrade of an Amplified 130-km Metro CWDM

Transmission System Using a Single LOA with 140-nm Bandwidth,” OFC ‘03

Tunable Filters – PromisingTechnology for Access

Active thin film (Aegis Semiconductor)

"Integrated into semiconductors

"Small size & power

Tunable Lasers

Fast tuning time is critical• State-of-the-art: ~5 ns over entire C-band

! Based on GCSR laser

! Digitally-controlled driver with overdriving pulse technique

* K. Shrikhande et al., "Performance Demonstration of a Fast-Tunable Transmitter and

Burst-Mode Packet Receiver for HORNET," OFC, ThG2-1, Mar., 2001.

Burst-Mode Receivers

Focus shifted from OLT to ONUs

One-chip solution preferred

• For mass deployment with ONUs

• Eventually, there will be no cost differencebetween continuous-mode & burst-mode receivers

III. Next-Generation Optical AccessArchitecture

Why Optical Access?

TDM-PON: Current-Generation OpticalAccess

Stanford University aCCESS (SUCCESS)

Why Optical Access?

Advantages of fiber as a transmissionmedium• Greater capacity (100s of Tb/s*)

• Smaller size and light weight

• Immune to electromagnetic interference

Fiber penetration in the networks• Already deployed in the backbone, the WANs, and

the MANs.

• Optical Ethernet is being introduced in LANs andwill spread to MANs and WANs.

* Mitra & Stark, Nature, vol 411, June 28, 2001.

TDM-PON Example - EPON

Proposed 1490nm downstream and1310 nm upstream (1550 free for WDMoverlays)

Data is transmitted in variable-lengthpackets of up to 1,518 bytes (i.e.,Ethernet frame)

Some packets may be intended for allof the ONUs (broadcast packets) or aparticular group of ONUs (multicastpackets)

Upstream traffic is managed utilizingTDM technology, in which transmissiontime slots are dedicated to the ONUs

Time slots are synchronized so thatupstream packets from the ONUs donot interfere with each other

The synchronization marker is a one-byte code that is transmitted every 2ms to synchronize the ONUs with theOLT

* Source: Alloptic

TDM-PON Example- APON (Lucent FTTB/H ONT)

Top View Rear View*

Front View Fiber

Cassette

* UNI cards are PCMCIA type.

Evolution of PONs

TDM-PONs

OLT

ONT

ONT

ONTWDM-PONs

OLT

ONT

ONT

ONT

?

SUCCESS* - Overview

Sponsored by ST/SNRC• Through F/M/A program

Next-generation optical access architecture based on• Hybrid WDM/TDM-PONs

• Ring+Tree topology

• Fast Tunable Components

Starting point: How to efficiently/smoothly upgradeTDM-PONs with those enabling technologies in thefuture?

* F-T. An et al., “SUCCESS: A next-generation hybrid WDM/TDM optical accessnetwork architecture,” IEEE/OSA JLT, vol. 22, no. 11, pp. 2557-2569, Nov. 2004.

SUCCESS – Major Objectives

Backward compatibility• To guarantee the coexistence of current-generation (TDM-

PON) and next-generation (WDM-PON) optical accesssystems in the same network

Easy upgradeability• To provide smooth migration paths:

! TDM-PON # Hybrid WDM/TDM-PON # WDM-PON

Protection/restoration capability• To support both residential/business users on the same

access infrastructure

SUCCESS – Features

Flexible Remote Nodes (RNs) with protection & restorationcapability

• Thin film filters as CWDM add/drop filters

• Passive splitter for TDM-PONs

• Athermal cyclic AWG for new WDM-PONs

Cost-effective ONUs for WDM-PON• No local light source (for DWDM)

! Optical bursts provided by OLT for upstream transmission, aremodulated by SOA at ONU, and send back to OLT.

! New MAC protocols designed for efficient bidirectional transmission

Integrated OLT• Based on tunable components

• Can support both TDM-PONs and WDM-PONs

Examples of Typical WDM-PONs

TX

RX

RX

ONUi

RX TX

ONUj

DEMUX MUX

RNk

… …

. . . . .

RXTX TX… …

MUX DEMUX

OLT

!

upstream downstream

2-fiber ring, 2 AWGs in 1 RN,

and 2 sets of wavelengths

RNAWG

AWG

RX TX

…

TX RX

…

TX RX

OLT

ONUi ONUj

.....

:Passive splitter

C :CWDM, splitterC

C

C

Single Fiber, bi-directional transmission

Network Migration Scenario under SUCCESS

CO

“Plain-old” PON

2$N

Flexible, protected, efficient

Access Networks.

Old ONUs and dist.

fibers are preserved.

W

W :DWDM, AWG

Co-Existing TDM/WDM-PONs

W

W

SUCCESS Architecture and Topology

Central

OfficeRN

RN

RN

RN

!’1, !2

!1

!2

!21

!22 !23

!’1

!’3, !4, …

!1, !2

!3, !4, …

!3

!’3

!3

!31

!32

!33

TDM-PON ONU

RN TDM-PON RN

WDM-PON ONU

RN WDM-PON RN

Virtually only 2 sets

of OLT resides in CO

Protection & restoration ispossible by using different !s

on east- and west- bound.

Wavelength Assignment

Maintain backward compatibility for TDM-PON ONUs and allownew WDM-PON ONUs to coexist

Little changes to current TDM-PON ONUs

! (nm)

O-Band E-Band S-Band C-Band L-Band

1260 1360 1460 1530 1565 1625

Upstream TDM traffic

Downstream TDM traffic

Downstream and Upstream WDM traffic,

one per ONU

CWDM Demux at OLT Tunable Lasers and

Filters at OLT

RN with Passive Splitter

2$N

Downstream:

1550.12nm

Upstream:

1310nm

RN15dB

4~32 ONUs

N$N

RN

ring ringring ring

Other !s

Downstream:

1550.12nm

Upstream:

1310nm

Downstream:

1550.92nm

Upstream:

1290nm

Other !s

ONU group #2 ONU group #1

N-2N-2

For TDM-PONs

For WDM-PONs

Based on Athermal cyclic AWG

BW of the thin-film band splitter (for DWDM !s):• Up/down-stream shares same !: (N-1)$%.

• Up/down-stream have different ! : (2$N-1)$ %.

RN with AWG

N-1 ONU N-1 ONU

AWG

.

.

.

.

.

.

!

ring ring

RN

Other !s

Semi-Passive RN forProtection/Restoration

10/90Elec.

Ctrl.

2$2

switch

N-1 N-1

Band splitters (A/D)

Passive splitter

or AWG

West East

Power from

one ONU

RN

ONU Structure for WDM-PON

SOA

distribution

fiber

Single port VCSOA

as modulator

SOA

2

3

1distribution

fiber

SOA may be used

as pre-amplifier

No local DWDM source for lowering cost

SOA as modulator and/or pre-amp

to the ring

WDM

coupler

CWDM

DWDM

Fast TLS

Pre-Amp

Post-Amp

Demux

TF

same

ISP

…

OLT Structure

Use tunable components to reduce transceiver counts and networkcost.

Each ISP can have TX/RX pair(s) to bundle/unbundle data inoptical domain.

The number of fast tunable laser sources depends on the numberof users, services, and the network load.

Scalability of SUCCESS - Wavelengths

Number of available wavelengths dictates number of users.

CWDM channels carry upstream data of TDM-PON, DWDM channels inC/L band carry both downstream and upstream data of WDM-PON.

Factors influencing number of available wavelengths:

• Channel spacing of AWG, attenuation profile of optical fiber, and opticalamplifier gain bandwidth.

Number

of

Available

DWDM

Wave-

lengths

Fiber Atten-uation,dB/km

AllWaveTM

CWDM

upstreamDWDM

Scalability of SUCCESS – Wavelengths (Continued)

Where• !C: # of channels for CWDM TDM-based upstream traffic,

• !D: # of channels for DWDM ONUs,

• %!: Channel spacing of AWG is (in GHz);

Note that• Total 18 CWDM wavelengths are available:

• With 20nm spacing and AllWaveTM fiber;

• Each nm corresponds to roughly 125GHz;

• For each !C corresponds to the number of 32$!C CWDM ONUs, and !D

means there are !D DWDM ONUs.

c

c

D!

!

!! "

#

$"$=

125)18(20

ONU1

ONU2

ONU3

SMF:2.2km SMF:15km SMF:5km

SMF:15kmSMF:2.2km

TLS:!2

TLS:!1

OBPF EDFA

thin-film A/D

circulator

passive splitter

OLT

ONU1, 2

SOA AM

75/25

Experimental Setup

RN

RN

RN

AWG

RN

PRBS

35km SMF Ring

1 OLT, 2 ONUs

800 ps

800 ps

Experimental ResultsDownstream Data Eye Diagram:

Upstream Data Eye Diagram:

2 ms

2 ms

leading edge ofCW burst on !1

leading edge ofupstream traffic on !1

2 ms

The timing diagram of packetized

transmission based on SUCCESS MAC:

Downstream

packets and CWbursts on !1

Downstream

packets and CWbursts on !2

Upstream

traffic monitored

at OLT

SUCCESS WDM-PON MAC Protocol

Design goal• To provide efficient bidirectional transmission over

half-duplex physical channel.

Challenges• Variable-length frames

• Time-sharing of the same channel for both up-and downstream traffic

• No separate control channel/frame structure

• No delay equalization! Need to reduce the impact of different RTTs.

SUCCESS WDM-PON Frame Formats

Delimiter Preamble

(01…01)

1-Bit

ID(=1)Ethernet Frame

CW

or

16-Bit

Grant

Overhead (= 24 Bits)

For

Downstream

For

UpstreamDelimiter Preamble

(01…01)

Overhead

Ethernet Frame 16-Bit

ReportEthernet Frame …

Delimiter Preamble

(01…01)

1-Bit

ID(=0)

Overhead

First Step - Sequential Scheduling

RX1

RX2

TX1

TX2

TX3 t0

RTT3

!1

!2

!4

G

!4!1

New transmission

scheduled!

t1

l1

RTT1

!2

!1

t

Example for 3 TXs, 2 RXs & 4 CHs

Sequential Scheduling – Pseudo Code

Begin

wait until a packet arrives;

set d = packet.destination, l = packet.length;

select i such that TX[i] <= TX[m] for all m = 1,…,M and m & i;

if packet is for upstream

select j such that RX[j] <=RX[n] for all n = 1,…,N and n & j;

set t = max(RX[j] + G – RTT[d], TX[i] + G, CH[d]);

set RX[j] = t + l + RTT[d]; /* update status variables */

schedule reception at time = t + RTT[d] with RX[j] via CH[d];

else /* packet is for downstream */

set t = max(TX[i] + G, CH[d]);

/* Common processing for both up- & downstream packet */

set CH[d] = t + l, TX[i] = t + l; /* update status variables */

schedule transmission at time = t with TX[i] via CH[d];

End

Simulation Environment

Based on OMNeT++:

• Object-oriented design! C++ based

• Messaging classes

• Statistics collection

• WDM capability! Supporting more than one links between nodes

• Optional graphic interface good for debugging

Simulator based on OMNeT++

Simulation - Setup

Network Configuration• 16 ONUs divided into 4 groups (with 4 ONUs per

each) and placed from the OLT 5 km, 10 km, 15km and 20 km, respectively.

MAC Parameters• Line rate: 10 Gbps

• Maximum grant size: 2 Mbits

• ONU timeout: 2 ms

• Guard band: 50 ns

• ONU queue size: 10 MB

Simulation - Setup

Traffic

• Arrival Process: Poisson

• Packet size distribution: Based on measurementtrace from MCI-backbone OC-3 links

• Ratio of downstream to upstream traffic: 2:1

Performance measures

• Throughput

• Average end-to-end packet delay

Simulation Results – Throughput

Upstream Throughput

Downstream Throughput

Simulation Results - Delay

Upstream Delay

Downstream Delay

Next Step - Batch Scheduling*

Improvements over sequential scheduling

• Schedule over multiple frames in VOQs with theearliest available TX and RX! Room for optimization & priority queueing to minimize wasted

resources for higher throughput and better fairness

Implementation Options

• Adaptive Batch Size! Varying upon queue length, packet dead line and so on

• Multiple sets of VOQs per ONU! To provide multiple QoS classes and better fairness between

up- and downstream traffic through priority queueing

* K. S. Kim et al, “Batch scheduling algorithm for SUCCESS WDM-PON,”Proc. of GLOBECOM 2004, Dallas, TX, USA, Nov. 2004.

Batch Scheduling – Timing Diagram

Arrival

Time

Scheduled

TX Time

Scheduling the 2nd batchand remnants from the 1stone.

Scheduling the 1st batch

1st batch 2nd batch 3rd batch

Batch Scheduling - OLT Structure

…Downstream

VOQs

…Upstream

VOQs Scheduler*

…Polling

VOQs

TX queue

(1 frame)

Tunable

Laser

TX1

Fiber

. .

.

TX queue

(1 frame)

Tunable

Laser

TXM

Pointer to a frame to

be scheduled next

* Scheduler maintains a list of

scheduled transmissions and

receptions where transmission &

reception times, VOQ #, CH #, RX #

and TX # are stored.

Scheduled framesTo RXs (control signals)

Initial Results - Throughput

Upstream Throughput

Downstream Throughput

Summary

Mismatch between current service/usage model andnetwork infrastructure is a driving force behind theparadigm shift in optical networking

• Towards flexible dynamically-reconfigurable optical networking

• Rapid developments in tunable optical components, CWDM, andBMRs make such dynamically-reconfigurable optical networkingfeasible.

• Advances in architectural study push those enabling technologiestowards the edge of the network.

SUCCESS is a joint research initiative for a next-generation optical access architecture

• Exploiting the benefit of flexible, dynamically-reconfigurableoptical networking in access

• Guaranteeing smooth transition paths from current TDM-PONs tofuture WDM-based optical access

Future Work

Subsystem and component level• Fast tunable lasers and receivers at OLT

• Fast modulation technique for SOA at ONU

System level• Efficient and fair scheduling algorithms

! Batch scheduling with adaptive batch period

! Theoretical scheduling algorithm and performance bounds

! Randomized version of batch scheduling algorithm

• Support of better QoS! Hierarchical scheduling

• 2nd-generation testbed with MAC! With upper layers for demonstration at application level

Thank You for Your Attendance!

For more information, please contact me

(kks@stanford.edu) or visit the following:•Personal home page: http://www.stanford.edu/~kks

•PNRL: http://pnrl.stanford.edu

•SNRC: http://snrc.stanford.edu