BurstMode 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 7 th, 2006

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

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

The Telecom Pendulum Wide Area Networks WAN Access MAN Broadband Access Networks Metropolitan Area Networks 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) 4

Where Is the Bottleneck? Home / Small Business Backbone ~ 10 s Gbit/s MAN (ISP) Access Router and PC’s ~ Gbit/s ~ 100 s Kbit/s DSL ~ 1 Mbit/s Cable ~10 Mbit/s FTTH 100 Mbit/s SONET Ethernet • Pressure to: Ø Ø Ø Increase access networks’ bandwidth v Even current TDM Passive Optical Networks (PONs) provide only about 25 Mbit/s per user (average). Integrate different types of traffic: v SONET base is large & circuit oriented, while most new traffic is bursty data. Minimize delay across networks and provide Qo. S for “Triple Play”. 5

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

Optical & Hybrid Broadband Access Networks Passive Optical Networks • Last-mile/first-mile distribution network • Reduces setup and maintenance costs • Increases bandwidth • Examples: Ø Verizon’s FIOS: Tree PON to the home (FTTH) or premises (FTTP) Ø AT&T’s U-Verse: FTTN (node or neighborhood) + VDSL to the home 7 Source: Telcordia

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: Ø Ø 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) End user Passive infrastructure … Splitter Central Office 8

Current PON Standards (all TDM) A/BPON GPON EPON Standard ITU G. 983 ITU G. 984 IEEE 802. 3 ah Packet/Cell Size 53 bytes 53 - 1518 bytes 64 ~ 1518 bytes Max Bandwidth 622 / 155 Mbit/s 2. 488 Gbit/s 1. 25 Gbit/s Typical rate 622 Mbit/s 1 Gbit/s Max PON splits 32 64 16 Layer 2 Traffic ATM Generic Ethernet Voice TDM Native TDM Vo. IP or TDM Video 1550 nm overlay RF or IP 1550 nm overlay Strengths Mature standards; Qo. S; Integration with SONET. Efficiency; Flexibility. Low cost chipsets; Easy integration with RPR. . Users to date ~1 M none yet ~ 97 K 2009 Expected ~ 11 M ~ 394 K ~ 5. 7 M Deployment US - Asia 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). 9 Sources: RHK PON IC Market Forecast.

Limitations of TDM PONs • Wavelength allocation in TDM PONs (A/BPON, GPON, EPON): Ø One wavelength for downstream data channel; Ø One wavelength for upstream data channel; Ø Optional additional wavelength for broadcast downstream video. • PONs provide high line rates, but shared among 16, 32 or 64 users. Ø In FIOS, downstream = 30 Mbps ; upstream = 5 Mbps per user (average) Optional downstream analog video overlay @ 1550 nm Downstream digital data @ 1490 nm or 1550 nm … 3 2 1 ONU 1 Feeder Fiber … OLT ONU 2 1 2 3 Upstream digital data @ 1310 nm ONU 3 10

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: Ø Ø Ø Rite. Net (AT&T, 1994); Multistage PON (Core. Com & Politecnico de Milano, 2000); SUCCESS (Stanford University Access, started in 2003) v v SUCCESS - DWA PON SUCCESS - HPON 11

SUCCESS-DWA: Architecture Separates upstream/ downstream traffics • • Dynamic Wavelength Allocation technique: Ø Using fast tunable lasers in the central office and assigning fixed wavelength to users to for dynamic bandwidth allocation among the users. Ø Exploiting wavelength band relationships for high scalability. Ø Cyclic AWG enables wavelength routing among multiple physical PONs. Hybrid TDM/WDM architecture Ø 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 Ø High network scalability Ø Cost sharing of equipments among multiple PONs Ø Statistical multiplexing gain due to large number of users • Quality of Service (Qo. S) can be provisioned with high scalability • Can span the range of capacities between conventional TDM PONs and full WDM PONs with graceful upgrades TDM PON SUCCESS-DWA Low Cost / Low Performance WDM PON High Cost / High Performance 13

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 FPGA PCB TL 1 MZ 1 TL 2 MZ 2 AWG OLT WDM traffic flow WDM Filter (DWA scheduling algorithm supporting Qo. S) PD CDR FPGA PCB ONU 14

SUCCESS – HPON: Architecture Hybrid TDM/WDM PON: Key goal - support both TDM and WDM PON w/ protection & restoration l 3, l 4, … Open Access: each ISP has its own set of OLTs at CO Central l 1, l 2 l 1 l’ 1 C l 3 Office l’ 1, l 2 l’ 3, l 4, … Low cost and scalability: use of centralized light sources, sharing expensive components l 2 C l 41 l 4 W l 21 l 43 Protection & restoration: ring topology W TDM-PON ONU C l 22 l 42 l 23 TDM-PON RN WDM-PON ONU W WDM-PON RN Smooth migration: old TDM-PON over CWDM channels and new WDM-PON (p 2 p) over DWDM channels can both be supported ISP – Internet Service Provider OLT – Optical Line Terminal CO – Central Office RN – Remote Node TDM – Time Division Multiplexing WDM – Wavelength Division ultiplexing PON – Passive Optical Network ONU – Optical Network Unit 15

SUCCESS-HPON: Research Summary • Network Architecture: Ø Ø Ø 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: Ø CLS approach proved at 1. 25 Gbit/s up and downstream. • MAC Protocol and Scheduling algorithms: Ø Ø Close to 100% throughput; Less than 2 ms delay in a 25 Km PON. 16

SUCCESS – HPON: Testbed Demonstration Thin-film add/drop WDM filters AWG downstream TLS: 1 SMF: 2. 2 km SMF: 15 km TLS: 2 Pattern Generator ONU 1 upstream SMF: 2. 2 km ONU 2 SMF: 5 km SMF: 15 km OBPF EDFA ONU 3 ONUs details: Scope OLT 17

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

Example: Metro Core network SBC (now AT&T net) • Architecture: Haul Metro Mesh Ring Long • 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: Ø Use of OADMs/ROADMs: flexible & cost-effective Ø Use of VCAT, LCAS, GFP: bandwidth efficiency USD Billion • Metro Packet Rings: RPR Ø For efficient transport of packets ADM : Add/Drop Multiplexer DCS: Digital Cross-Connect Switch Legacy SONET Next-Gen SONET OADM: Optical Add/Drop Multiplexer ROADM: Re-configurable OADM SONET: Synchronous Optical Network LCAS: Link Capacity Adjustment Scheme GFP: Generic Framing Procedure RPR: Resilient Packet Rings VCAT: Virtual concatenation SDH: Synchronous Digital Hierarchy 19

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

Metro Optical Network Architecture (MONA) • Requirements of new metro architecture: Ø Ø • 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 21

MONA: Optical Burst Transport (OBT) • Logical-Mesh-over-Physical Ring (LMPR) Architecture & Token based media access • Burst Size & Duration : 200 k. B - 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 CH 4 OBT Control channel 3 4 OBT LMPR (OBT) 4 OBT 3 2 OBT router 1 2 Data channel 2 3 4 OBT CH 2 CH 3 node 4 node 3 node 2 BURST SCHEDULER Guard time Virtual Output Queues (VOQs) 22

MONA: Ethernet over OBT Network Testbed From / To OBT node Node 2 Node 1 From / To PC CTRL RX CTRL TX DATA RX Node 0 DATA TX Ctrl plane • 3 Nodes • 65 km Circumference • 100 GHz ITU grid ’s • 2. 5 Gbps payload channels • 1. 25 Gbps control channel 23

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

Burst-Mode Transmission Path Photo Diode Laser Off Burst Enable t Data MUX Retimer ÷N Frequency Synthesizer TXDr Receiver (RX) Transmitter (TX) Payload Preamble TIA Guard time LIA Decision Circuit DMUX Clock Recovery t Key Functional Blocks*: 1. TX: Transmitter Driver 2. RX: Level Recovery 3. RX: Clock and Data Recovery * Electronics only 25 Data

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 Laser (CW) Data Burst EAM Mod External Mod or Switch Optical output • Access is cost sensitive single mod for burst & data. Burst Data Direct Mod Laser (CW) Optical output 26

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 enable Optical Power t Transient of AGC BM-LD Burst For monitoring output power Controlled power level t 27

Level Recovery Function • Recover signal level for subsequent processing. Continuous Transmission • Fast level recovery is not required. • The received signal level is constant Ø Continuous signaling by bit stuffing. Ø Line coding DC-balance & sufficient data transition density Continuous Burst-Mode Transmission • Different bursts have different power levels: Ø Large dynamic range Ø Fast response to each incoming burst No idle bits Varying power levels 28

Burst-Mode Level Recovery • Specially designed trans-impedance amplifier (TIA) and/or limiting amplifier (LIA), that can rapidly and automatically adjust the gain. • Two schemes can be used: Ø Ø Feedback Feedforward • Still a challenge, especially at high bit rates. Received bursts (Optical) Bursts after level recovery (Electrical) TIA t LIA Level Recovery t 29

Example of Level Recovery Circuit Received signal power = -30 d. Bm IC 1 IC 2 • 1. 25 Gbps level recovery IC (0. 25 um Si. Ge Bi. CMOS) • Feedback TIA & Feedforward LIA design. • The TIA: Ø Feedback resistance adjusted with signal level. Ø Fast feedback realized by hysteresis comparator. • The LIA: Ø AOC first detects the offset of differential paths. Ø Following circuit cancels the offset. Received signal power = -24 d. Bm Received signal power = -10 d. Bm 30 M. Nakamura, Y. Imai, Y. Umeda, J. Endo, Y. Akatsu, “ 1. 25 Gb/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): Ø Line coding technique: 8 B 10 B maximum 5 CIDs • Must tolerate phase noise (jitter) Burst-mode Transmission • Additionally, short acquisition time- i. e. fast clock recovery. Decision Circuit 0101… t Clock Recovery 31

Clock Recovery (Cont’d) • PLL clock recovery: typically requires thousands of bits Ø E. g. If 1, 000 bits are required for PLL to recover clock v v Longest Ethernet frame (1, 500 Bytes) overhead = 1000/12000 = 8. 3% Shortest Ehternet frame (64 Bytes) overhead = 1000/512 = 195% • Feedfoward architectures to enhance recovery speed Ø Ø Ø 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 32

PNRL Clock Recovery (Example) Control Logic DATAin MUX High-speed DLL DATAout Phase Generator CLKref • • 1. 25 Gbps Clock Recovery circuit designed for TDM-PON by PNRL. Hybrid architecture composed of two parts: Ø Ø • CLKout Chip Layout (0. 18 um CMOS technology) 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. CDR IC and PCB 7 clock cycle (~6 ns @ 1. 25 Gbps) Phase Change (1000) 33 Y Hsueh, W. Shaw, “A Novel 1. 25 Gbps Burst-mode Clock Recovery Circuit for TDMPON”, Photonics Technology Letter (Submitted)

Summary of Continuous and Burst-mode trasnmission Continuous Transmission Burst-mode Transmission Transmitter Driver • Only data modulation • Monitors and regulates averaged power • Burst + Data Modulation • Fast monitoring of instant power level • Fast AGC Level Recovery • Fast level recovery is not needed • Large dynamic range • Constant transmission • Fast response to each incoming burst • Tolerance to CID within a packet/burst Clock Recovery • PLL is widely used • Slow recovery • Good jitter tolerance • Requires fast clock recovery • Trade-off between recovery speed & jitter tolerance 34

TDM-PON Standard Specification for Burst-Mode Transceivers Guard time Avg. Recv’d power RX sensitivity GPOM 25. 6 ns -7 d. Bm -28 d. Bm EPON 512 ns -6 d. Bm -27 d. Bm • • • RX settling time Dynamic range CID toleran ce TON TOFF 44 bits 21 d. B 72 bits 12. 8 ns 500 bits 20 d. B 5 bits 512 ns Level and Clock Recovery Related Ext. ratio (min) Avg. OFF power (max) Average launch power 10 d. B -38 d. Bm +3 d. Bm(max) -2 d. Bm(min) 6 d. B -45 d. Bm +4 d. Bm(max) -1 d. Bm(min) Laser Driver Related GPON: ITU-T 984 EPON: IEEE 802. 3 ah 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 8 B 10 B 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 Requirements for Next-Gen WDM / TDM Access & Metro Networks • Next-generation TDM/WDM Access: Ø Ø Both downstream and upstream are burst-mode transmission; compared to TDM-PON only upstream. Data rate: 2. 5 Gbps to 10 Gbps. Recover both phase and frequency. CMOS technology is desirable, especially in ONUs. • Next-generation MAN: Ø No standards or specifications for BM-MAN yet. 36

Integration of the Functional Blocks • Separate the noisy and sensitive functional blocks on different substrates Ø Noisy: MUX, DMUX (high-speed digital), Transmitter Drive (high slew rate) Ø Sensitive: TIA, LIA • Burst mode transceivers can be divided into 3 or 4 ICs Ø 4 ICs v (a) Transmitter Drive (TX) v (b) Serializer (TX) v (c) TIA+LIA (RX) v (d) Deserializer (RX) Ø 3 ICs v (a) Laser Drive (TX) v (b) TIA+LIA (TX) v (c) Ser. Des (TRX) Burst Enable Serializer MUX Retimer ÷N Frequency Synthesizer DMUX Decision Circuit TX LDr LIA TIA RX Clock Recovery De-serializer Ser. Des 37

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: Ø Burst-mode component challenges: v Burst-Mode Transmitter Driver; v Burst-Mode Level Recovery; v Burst-Mode Clock Recovery. • Our initial research focus @ CIS: high speed burstmode clock recovery. 38

THANK YOU Prof. Leonid G. Kazovsky http: //pnrl. stanford. edu kazovsky@stanford. edu 39