Burst-Mode Optical Networks: Recent Developments & Future Components Needed

Burst-Mode Optical Networks: Recent Developments & Future Components Needed Prof. Leonid Kazovsky Photonics & Networking Research Laboratory Department of Electrical Engineering Stanford University CIS November 7th, 2006

Outline • Optical Networking • Broadband Access Networks • Current Access Networks • PNRL Research in Burst-Mode Access Networks • Metropolitan Area Networks • Current MANs • PNRL Research in Burst-Mode MANs • Burst-Mode Components • Summary • Optical Networking • Broadband Access Networks • Current Access Networks • PNRL Research in Burst-Mode Access Networks • Metropolitan Area Networks • Current MANs • PNRL Research in Burst-Mode MANs • Burst-Mode Components • Summary

Network Hierarchy • Backbone: • Continent-to-Continent • Coast-to-Coast • Distances > 1000km • 10Gbit/s ~ Tbit/s • Metro: • Within cities or multiple cities in the same region • Distances ~200km • 1Gbit/s ~ 40Gbit/s • Access: • To residence or business • Distances ~20km • 100Kbit/s ~ 1Gbit/s • Local Area: • Within office/home • Distances ~100m • 10 Mbit/s ~ 1Gbit/s Residential DSL, Cable or FTTH Corporate enterprise clients Fixed voice, cellular ISPs LAN LAN Illustration from Sorrento Networks White Paper (edited)

The Telecom Pendulum Photonics and Networking Research Lab (PNRL) is focusing on metropolitan area networks and broadband optical access networks – different from most other research groups (their focus: long distance) Broadband Access Networks Wide Area Networks Access WAN MAN Metropolitan Area Networks

Where Is the Bottleneck? Home / Small Business • Pressure to: • Increase access networks’ bandwidth • Even current TDM Passive Optical Networks (PONs) provide only about 25 Mbit/s per user (average). • Integrate different types of traffic: • SONET base is large & circuit oriented, while most new traffic is bursty data. • Minimize delay across networks and provide QoS for “Triple Play”. Backbone MAN (ISP) Access Router and PC’s ~ 100s Kbit/s DSL ~ 1 Mbit/s Cable ~10 Mbit/s FTTH 100 Mbit/s ~ Gbit/s SONET Ethernet ~ 10s Gbit/s

Outline • Optical Networking • Broadband Access Networks • Current Access Networks • PNRL Research in Burst-Mode Access Networks • Metropolitan Area Networks • Current MANs • PNRL Research in Burst-Mode MANs • Burst-Mode Components • Summary

Optical & Hybrid Broadband Access Networks • Examples: • Verizon’s FIOS: Tree PON to the home (FTTH) or premises (FTTP) • AT&T’s U-Verse: FTTN (node or neighborhood) + VDSL to the home • Passive Optical Networks • Last-mile/first-mile • distribution network • Reduces setup and • maintenance costs • Increases bandwidth Source: Telcordia

End user Passive infrastructure … Splitter Central Office Example: Passive Optical Networks (PON) • Passive components: low cost, easy maintenance, high reliability. • Tree topology: better penetration, lower costs. • Signal transmission is limited by splitting loss. • TDM PONs: • Low cost • Two wavelengths: one downstream and one upstream • Downstream: Broadcast-and-select bursts (variable size) • Upstream: TDMA burst transmission and reception (in BPON duration: multiples of 53 bytes, 2.73 s)

Current PON Standards (all TDM) PON users today by region: Asia Pacific 86%, North America 11%, Europe & Middle East 3 %. (Note that these figures do not include other broadband options). Sources: RHK PON IC Market Forecast.

Limitations of TDM PONs • Wavelength allocation in TDM PONs (A/BPON, GPON, EPON): • One wavelength for downstream data channel; • One wavelength for upstream data channel; • Optional additional wavelength for broadcast downstream video. • PONs provide high line rates, but shared among 16, 32 or 64 users. • In FIOS, downstream = 30Mbps ; upstream = 5 Mbps per user (average) Optional downstream analog video overlay @ 1550nm ONU 1 Downstream digital data @ 1490nm or 1550nm … 3 2 1 Feeder Fiber OLT ONU 2 … 2 3 1 ONU 3 Upstream digital data @ 1310nm

WDM PONs • WDM can enhance capacity. • A challenge: how to migrate from TDM-PONs to WDM-PONs in a cost-effective, scalable and flexible way. • Examples of WDM-PON research projects: • RiteNet (AT&T, 1994); • Multistage PON (CoreCom & Politecnico de Milano, 2000); • SUCCESS (Stanford University Access, started in 2003) • SUCCESS - DWA PON • SUCCESS - HPON • WDM can enhance capacity. • A challenge: how to migrate from TDM-PONs to WDM-PONs in a cost-effective, scalable and flexible way. • Examples of WDM-PON research projects: • RiteNet (AT&T, 1994); • Multistage PON (CoreCom & Politecnico de Milano, 2000); • SUCCESS (Stanford University Access, started in 2003) • SUCCESS - DWA PON • SUCCESS - HPON

SUCCESS-DWA: Architecture Separates upstream/ downstream traffics • Dynamic Wavelength Allocation technique: • Using fast tunable lasers in the central office and assigning fixed wavelength to users to for dynamic bandwidth allocation among the users. • Exploiting wavelength band relationships for high scalability. • Cyclic AWG enables wavelength routing among multiple physical PONs. • Hybrid TDM/WDM architecture • Highly evolutional architecture by reconfiguring the numbers of TLs, physical PONs, and end users per AWG.

SUCCESS DWA: Research Summary • SUCCESS-DWA : a hybrid WDM/TDM PON with high flexibility • Utilizes existing arbitrary field-deployed PON infrastructures • Dynamically shares bandwidth and resources across multiple physical passive optical networks • High network scalability • Cost sharing of equipments among multiple PONs • Statistical multiplexing gain due to large number of users • Quality of Service (QoS) can be provisioned with high scalability • Can span the range of capacities between conventional TDM PONs and full WDM PONs with graceful upgrades SUCCESS-DWA TDM PON WDM PON Low Cost / Low Performance High Cost / High Performance

AWG ONU SUCCESS-DWA: Testbed Demonstration • Streaming MPEG video/audio demonstration. FPGA: Field Programmable Gate Array PCB: Printed Circuit Board TL: Tunable Laser CDR: Clock and Data Recovery PD: Photo Diode MZ: Mech-Zender Modulator AWG: Array Waveguide Grating TL1 MZ1 FPGA PCB OLT TL2 MZ2 WDM traffic flow WDM Filter FPGA PCB (DWA scheduling algorithm supporting QoS) PD CDR

SUCCESS – HPON: Architecture Hybrid TDM/WDM PON: Key goal - support both TDM and WDM PON w/ protection & restoration l3, l4, … l’3 Central Office Open Access: each ISP has its own set of OLTs at CO l3 l1, l2 C l’3, l4, … l’1, l2 l41 Low cost and scalability: use of centralized light sources, sharing expensive components l4 l1 l42 C l’1 W l43 l2 Protection & restoration: ring topology W TDM-PON ONU TDM-PON RN C l21 WDM-PON ONU l22 l23 WDM-PON RN W Smooth migration: old TDM-PON over CWDM channels and new WDM-PON (p2p) over DWDM channels can both be supported ISP – Internet Service Provider TDM – Time Division Multiplexing OLT – Optical Line Terminal WDM – Wavelength Division ultiplexing CO – Central Office PON – Passive Optical Network RN – Remote Node ONU – Optical Network Unit

SUCCESS-HPON: Research Summary • Network Architecture: • TDM to WDM Migration → Hybrid WDM / TDM-PON with support for legacy TDM ONUs; • Evolution from tree to ring → Improved protection • Centralized Light Sources → no need for tunable components at the ONUs; • Cost-effectiveness → each OLT provides service to many users with just a few tunable components; • Scalability → to serve more users or more traffic, simply add more tunable transceivers at the OLT; • Physical layer: • CLS approach proved at 1.25 Gbit/s up and downstream. • MAC Protocol and Scheduling algorithms: • Close to 100% throughput; • Less than 2ms delay in a 25 Km PON.

SUCCESS – HPON:Testbed Demonstration Thin-film add/drop WDM filters downstream AWG TLS: 1 SMF:2.2km SMF:15km TLS: 2 Pattern Generator ONU1 ONU2 SMF:5km upstream SMF:2.2km SMF:15km OBPF EDFA ONU3 ONUs details: OLT Scope

USD Billion Legacy SONET Next-Gen SONET Example: Metro Core network • Architecture: Long HaulMetro MeshRing • SONET/SDH rings- Synchronous, self-healing & designed for delay sensitive and fixed-bandwidth traffic • Legacy SONET: Use of electronic ADMs and DCS • Next Gen SONET: • Use of OADMs/ROADMs: flexible & cost-effective • Use of VCAT, LCAS, GFP: bandwidth efficiency • Metro Packet Rings: RPR • For efficient transport of packets SBC (now AT&T net) ADM : Add/Drop Multiplexer LCAS: Link Capacity Adjustment Scheme DCS: Digital Cross-Connect Switch GFP: Generic Framing Procedure OADM: Optical Add/Drop Multiplexer RPR: Resilient Packet Rings ROADM: Re-configurable OADM VCAT: Virtual concatenation SONET: Synchronous Optical Network SDH: Synchronous Digital Hierarchy

Move away from SONET circuits Electronic IP Processing on WDM rings: Example: 7 nodes with 32 s (10Gbps per ) Giga-bit routers (640Gbps or 770 Mpps lookup) Not cost-effective; 40% transit traffic at each node 308 Mega-packets per second (Mpps) “wasted” lookup Not scalable: Need 20x scale-up on electronic pkt lookup when 160 s (40 Gbps per ). Possible solution for data-based metro networks Router - Juniper T640 Does it solve the problem?

Metro Optical Network Architecture (MONA) • Requirements of new metro architecture: • Adaptive data transport based on bursts– for bursty traffic • On-demand, instantaneous BW provisioning • Efficient support for video distribution • Concept can be extended to the Core – OBS • How short the reallocation time should be? Reallocation Time (few msec) Peak Mean Observation Time

CH4 CH2 CH3 Control channel 3 4 3 2 OBT OBT Data channel 4 2 2 OBT OBT OBT OBT OBT OBT OBT OBT node 4 node 3 node 2 1 3 BURSTSCHEDULER LMPR 4 (OBT) OBT OBT OBT OBT OBT OBT OBT OBT Guard time Virtual Output Queues (VOQs) OBT OBT OBT OBT OBT OBT OBT OBT MONA: Optical Burst Transport (OBT) • Logical-Mesh-over-Physical Ring (LMPR) Architecture & Token based media access • Burst Size & Duration : 200 kB - 640 s (@ 2.5 Gbps) • Single control channel - Lower bit rate (1.25 Gbps), continuous, out-of-band • Multiple payload data channels - Higher bit rate (2.5 Gbps), Burst Transmission • PNRL demonstrated 2.5 Gbps, Ethernet over OBT network testbed (Jun ‘06) OBT router

CTRL RX CTRL TX DATA RX DATA TX Ctrl plane MONA: Ethernet over OBT Network Testbed From / To OBT node Node 2 Node 1 From / To PC Node 0 • 3 Nodes • 65 km Circumference • 100 GHz ITU grid ’s • 2.5 Gbps payload channels • 1.25 Gbps control channel

Burst-Mode Transmission Path Photo Diode Laser Diode Laser Off Burst Enable t TXDr Data MUX Retimer Frequency Synthesizer ÷N Receiver (RX) Transmitter (TX) Payload LIA TIA Decision Circuit DMUX Data Preamble Guard time Clock Recovery • Key Functional Blocks*: • TX: Transmitter Driver • RX: Level Recovery • RX: Clock and Data Recovery t * Electronics only

Transmitter Driver Function • Turns light on/off as determined by data and bursts. • Metro requires higher speed and performance  separate mod’s for data and burst Data Burst Laser (CW) EAM Mod External Mod or Switch Optical output • Access is cost sensitive  single mod for burst & data. Burst Direct Mod Laser (CW) Data Optical output

Access Transmitter Driver “Old” Technology: Continuous Transmission • Laser not fully turned off when “ZERO” to reduce chirping. • Transmitter driver monitors and regulates the average power. • Adequate switching speed to minimize ISI. • Tolerance of output voltage swing across the laser diode. New Technology: Burst-Mode Transmission • Complete turn off between bursts is a must. • Fast monitoring mechanism of the instantaneous optical power level and AGC. Laser Off Burst Burst Burst enable t BM-LD Optical Power Transient of AGC Burst Controlled power level t For monitoring output power

Level Recovery Function • Recover signal level for subsequent processing. Continuous Transmission • Fast level recovery is not required. • The received signal level is constant • Continuous signaling by bit stuffing. • Line coding DC-balance &sufficient data transition density Continuous Burst-Mode Transmission • Different bursts have different power levels: • Large dynamic range • Fast response to each incoming burst No idle bits Varying power levels

Burst-Mode Level Recovery • Specially designed trans-impedance amplifier (TIA) and/or limiting amplifier (LIA), that can rapidly and automaticallyadjust the gain. • Two schemes can be used: • Feedback • Feedforward • Still a challenge, especially at high bit rates. Received bursts (Optical) Bursts after level recovery (Electrical) LIA TIA t t Level Recovery

Example of Level Recovery Circuit Received signal power = -30dBm IC2 IC1 • 1.25 Gbps level recovery IC (0.25um SiGe BiCMOS) • Feedback TIA & Feedforward LIA design. • The TIA: • Feedback resistance adjusted with signal level. • Fast feedback realized by hysteresis comparator. • The LIA: • AOC first detects the offset of differential paths. • Following circuit cancels the offset. Received signal power = -24dBm Received signal power = -10dBm M. Nakamura, Y. Imai, Y. Umeda, J. Endo, Y. Akatsu, “1.25Gb/s Burst-Mode Receiver ICs for Quick Response for PON System”, IEEE International Solid-State Circuit Conf.(ISSCC) 2005

Clock Recovery Function Recover clock for data sampling Continuous Transmission • Phase-locked loop (PLL) locks to the received signal. • Must work with many consecutive identical digits (CIDs): • Line coding technique: 8B10B  maximum 5CIDs • Must tolerate phase noise (jitter) Burst-mode Transmission • Additionally, short acquisition time- i.e. fast clock recovery. Decision Circuit 0101… t Clock Recovery

Clock Recovery (Cont’d) • PLL clock recovery: typically requires thousands of bits • E.g. If 1,000 bits are required for PLL to recover clock • Longest Ethernet frame (1,500 Bytes)  overhead = 1000/12000 = 8.3% • Shortest Ehternet frame (64Bytes)  overhead = 1000/512 = 195% • Feedfoward architectures to enhance recovery speed • Gated VCO • Over sampling • Gated bit line • However, feedforward architectures suffer from poor jitter tolerance. Preamble Payload Received signal (after level recovery) Preamble Payload Clock Recovery Recovered Clock

PNRL Clock Recovery (Example) • 1.25 Gbps Clock Recovery circuit designed for TDM-PON by PNRL. • Hybrid architecture composed of two parts: • Using over-sampling technique for coarse phase recovery (feedforward) • fast delay lock loop for fine phase recovery (feedback) • Can recover clock in 7 clock cycles. Control Logic DATAin High-speed DLL MUX DATAout Phase Generator Chip Layout (0.18 um CMOS technology) CDR IC and PCB CLKref CLKout 7 clock cycle (~6ns @ 1.25Gbps) Phase Change (1000) Y Hsueh, W. Shaw, “A Novel 1.25Gbps Burst-mode Clock Recovery Circuit for TDM-PON”, Photonics Technology Letter (Submitted)

Summary of Continuous and Burst-mode trasnmission

TDM-PON Standard Specification for Burst-Mode Transceivers Level and Clock Recovery Related Laser Driver Related • GPON: ITU-T 984 • EPON: IEEE 802.3ah • Guard time is the period between two subsequent bursts received by the OLT receiver • The receiver settling time includes both level recovery and clock recovery • The receiver sensitivity is specified as PIN diode is used. • Unlike EPON which uses 8B10B line code, GPON uses scrambling scheme so that the CID number has higher limit (while the transmission efficiency is higher) • TON is the max time to turn on the laser diode • TOFF is the max time to turn off the laser diode • Extinction ratio is applied to the logic ZERO’s and ONE’s in a burst

Performance Requirementsfor Next-Gen WDM / TDM Access & Metro Networks • Next-generation TDM/WDM Access: • Both downstream and upstream are burst-mode transmission; compared to TDM-PON only upstream. • Data rate: 2.5 Gbps to 10Gbps. • Recover both phase and frequency. • CMOS technology is desirable, especially in ONUs. • Next-generation MAN: • No standards or specifications for BM-MAN yet.

LIA TIA Integration of the Functional Blocks • Separate the noisy and sensitive functional blocks on different substrates • Noisy: MUX, DMUX (high-speed digital), Transmitter Drive (high slew rate) • Sensitive: TIA, LIA • Burst mode transceivers can be divided into 3 or 4 ICs • 4 ICs • (a) Transmitter Drive (TX) • (b) Serializer (TX) • (c) TIA+LIA (RX) • (d) Deserializer (RX) • 3 ICs • (a) Laser Drive (TX) • (b) TIA+LIA (TX) • (c) SerDes (TRX) Burst Enable Serializer LDr TX MUX Retimer Frequency Synthesizer ÷N RX DMUX Decision Circuit Clock Recovery De-serializer SerDes

Summary • Current trend: Access and Metro networks • Burst-mode optical networks are being deployed in TDM –PONs, likely to flourish there and penetrate metro networks (core?) • PNRL system experiments point to: • Burst-mode component challenges: • Burst-Mode Transmitter Driver; • Burst-Mode Level Recovery; • Burst-Mode Clock Recovery. • Our initial research focus @ CIS: high speed burst-mode clock recovery.

THANK YOU Prof. Leonid G. Kazovsky http://pnrl.stanford.edu kazovsky@stanford.edu

Burst-Mode Optical Networks: Recent Developments & Future Components Needed