- Seminar, Dept. of Electrical and Computer Eng., University of California, Davis, CA, USA, May 14, 2004. - Seminar, Dept. of Electrical and Systems Eng., Washington University in St. Louis, St. Louis, MO, USA, Dec. 3, 2004.

1. On The Next-Generation
Optical Access Architecture
Joseph Kim
AST, 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

2. I. ST and SNRC Introduction
Overview of STMicroelectronics
Overview of Stanford Networking Research
Center

4. Advanced System Technology
Mission
• To provide the advanced system
knowledge able to establish ST as the
system on a chip leading company in the
market for the products of the next decade
Role
• To provide the Company with long-term core
business and leadership in key markets

5. SAN JOSE’
SAN DIEGO
CATANIAGRENOBLE
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 in
demonstrator
Integration of building blocks
Performance (efficiency, QoS)
testing
Service demonstration
GBRA
GXT0
CPA
GLTA Board GNTA Board
GBLA
LD+
AFE
PD+
AFE
WDM
GXTP
NT version
PD+
AFE
LD+
AFE
WDM
CDR
GXTP
LT
version
LD
Driver
ARM
Designed
by STM
Designed
by STM
Designed
by Intec
Designed
by IntecSystem Info control
PTSP OBC PTSP OBC
Designed
by ABell
Designed
by ABell
1.25 Gbps
622 MbpsGBRA
GXT0
CPA
GLTA Board GNTA Board
GBLA
LD+
AFE
PD+
AFE
WDM
GXTP
NT version
PD+
AFE
LD+
AFE
WDM
CDR
GXTP
LT
version
LD
Driver
ARM
Designed
by STM
Designed
by STM
Designed
by Intec
Designed
by IntecSystem Info control
PTSP OBC PTSP OBC
Designed
by ABell
Designed
by ABell
1.25 Gbps
622 Mbps
SYMPHATI
Symmetrical PON at high bit rate
Specify and design chipset for 1.25
Gbps upstream GPON - Class B
Lab demo at 622 Mb/s upstream
APON system

6. MEMS – free space
Bubble switch
ST Competences in Optics - 1
ST Competences in Optics – 2

7. 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

8. 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

9. 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-Mode
Communications
Examples
Enabling Technologies

10. 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 of
it)
• Rapid development in enabling technologies
! Tunable optical components
! Burst-mode communications
! Optical packet/burst/flow switching
Dynamically-reconfigurable networks
better meet varying user demands even
with fewer resources!
Traditional Way of Using Wavelengths
TX
TX
TX
TX
RX
RX
RX
RX
SW SW

11. Optical Network with
Passive/Semi-passive Nodes
New Way of Using Wavelengths
Tunable
TX
SW
Tunable
TX
SW
Tunable
TX
SW
Fixed
RX
SW
Fixed
RX
SW
Fixed
RX
SW
Continuous-Mode vs. Burst-Mode
Communications
TX RXSW SW
...010110100101110100101001001010101111101001010101…
SONET/SDH
Packet Packet Packet
RX SW
10011…0110
Packet Packet Packet
011…010 011…010

12. 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-3
interface
Ethernet
interface
ATM
over OC-3
interface
Traffic destined to this node
should 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.

13. Tunable
Transmitter
!1
POP
Access 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

14. 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
1
6
2
6
3
6
4
TL: Tunable Laser
Enabling Technologies
Common denominator in technologies enabling
flexible, dynamically-reconfigurable optical
networks
• CWDM
• Tunable Filters
• Tunable Lasers
• Burst-Mode Receivers (BMRs)
The paradigm shift pushes these technologies
towards the edge of the networks!

15. 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 – Promising
Technology for Access
Active thin film (Aegis Semiconductor)
"Integrated into semiconductors
"Small size & power

16. 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 difference
between continuous-mode & burst-mode receivers

17. III. Next-Generation Optical Access
Architecture
Why Optical Access?
TDM-PON: Current-Generation Optical
Access
Stanford University aCCESS (SUCCESS)
Why Optical Access?
Advantages of fiber as a transmission
medium
• 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 and
will spread to MANs and WANs.
* Mitra & Stark, Nature, vol 411, June 28, 2001.

18. TDM-PON Example - EPON
Proposed 1490nm downstream and
1310 nm upstream (1550 free for WDM
overlays)
Data is transmitted in variable-length
packets of up to 1,518 bytes (i.e.,
Ethernet frame)
Some packets may be intended for all
of the ONUs (broadcast packets) or a
particular group of ONUs (multicast
packets)
Upstream traffic is managed utilizing
TDM technology, in which transmission
time slots are dedicated to the ONUs
Time slots are synchronized so that
upstream packets from the ONUs do
not interfere with each other
The synchronization marker is a one-
byte code that is transmitted every 2
ms to synchronize the ONUs with the
OLT
* Source: Alloptic
TDM-PON Example
- APON (Lucent FTTB/H ONT)
Top View Rear View*
Front View Fiber
Cassette
* UNI cards are PCMCIA type.

19. Evolution of PONs
TDM-PONs
OLT
ONT
ONT
ONT
WDM-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 upgrade
TDM-PONs with those enabling technologies in the
future?
* F-T. An et al., “SUCCESS: A next-generation hybrid WDM/TDM optical access
network architecture,” IEEE/OSA JLT, vol. 22, no. 11, pp. 2557-2569, Nov. 2004.

20. SUCCESS – Major Objectives
Backward compatibility
• To guarantee the coexistence of current-generation (TDM-
PON) and next-generation (WDM-PON) optical access
systems 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 & restoration
capability
• 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, are
modulated 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

21. 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
RN
AWG
AWG
RX TX
…
TX RX
…
TX RX
OLT
ONUi ONUj
.....
:Passive splitter
C :CWDM, splitter
C
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

22. SUCCESS Architecture and Topology
Central
Office
RN
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 is
possible by using different !s
on east- and west- bound.
Wavelength Assignment
Maintain backward compatibility for TDM-PON ONUs and allow
new 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

23. RN with Passive Splitter
2$N
Downstream:
1550.12nm
Upstream:
1310nm
RN
15dB
4~32 ONUs
N$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

24. Semi-Passive RN for
Protection/Restoration
10/90
Elec.
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

25. 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 network
cost.
Each ISP can have TX/RX pair(s) to bundle/unbundle data in
optical domain.
The number of fast tunable laser sources depends on the number
of 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 in
C/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 optical
amplifier gain bandwidth.
Number
of
Available
DWDM
Wave-
lengths
Fiber
Atten-
uation,
dB/km
AllWaveTM
CWDM
upstream
DWDM

26. 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

27. 800 ps
800 ps
Experimental Results
Downstream Data Eye Diagram:
Upstream Data Eye Diagram:
2 ms
2 ms
leading edge of
CW burst on !1
leading edge of
upstream traffic on !1
2 ms
The timing diagram of packetized
transmission based on SUCCESS MAC:
Downstream
packets and CW
bursts on !1
Downstream
packets and CW
bursts 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.

28. 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
Upstream
Delimiter Preamble
(01…01)
Overhead
Ethernet Frame 16-Bit
Report
Ethernet 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

29. 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

30. 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, 15
km 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

31. Simulation - Setup
Traffic
• Arrival Process: Poisson
• Packet size distribution: Based on measurement
trace 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

32. Simulation Results - Delay
Upstream Delay
Downstream Delay
Next Step - Batch Scheduling*
Improvements over sequential scheduling
• Schedule over multiple frames in VOQs with the
earliest 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.

33. Batch Scheduling – Timing Diagram
Arrival
Time
Scheduled
TX Time
Scheduling the 2nd batch
and remnants from the 1st
one.
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 frames
To RXs (control signals)

34. Initial Results - Throughput
Upstream Throughput
Downstream Throughput
Summary
Mismatch between current service/usage model and
network infrastructure is a driving force behind the
paradigm shift in optical networking
• Towards flexible dynamically-reconfigurable optical networking
• Rapid developments in tunable optical components, CWDM, and
BMRs make such dynamically-reconfigurable optical networking
feasible.
• Advances in architectural study push those enabling technologies
towards the edge of the network.
SUCCESS is a joint research initiative for a next-
generation optical access architecture
• Exploiting the benefit of flexible, dynamically-reconfigurable
optical networking in access
• Guaranteeing smooth transition paths from current TDM-PONs to
future WDM-based optical access

35. 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