Passive Optical Networks - materias.fi.uba.ar

1 Tutorial Passive Optical Networks Authors: Fabio Neri Jorge M. Finochietto Passive Optical Networks Contents Introduction Motivation 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 Introduction Passive Optical Networks Passive Optical Networks The Broadband Connected Household Interactive Ethernet Gaming 10-50 Mb/s Video- Conference Set Top Box 2x5 Mb/s Computers O/E IP. TV-channels +. 100 Mb/s VoD services Telephon 2x20 Mb/s e Triple Play Real Estate services TV. La ook E n on Al Home b Lo un in m HDTV. ar er ito station ck dr g m gy rin y DVR. g Passive Optical Networks Access network 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).

2 WiFi/WiMax Cellular Networks Optical access Networks Passive Optical Networks xDSL Solutions Largely deployed nowadays Use of existing copper lines Smooth migration/upgrade of current network Bandwidth and reach are limited! Data Rate, Mbps 52. VDSL. Shannon's information theorem . 24 (S/N-limited, here: crosstalk). 12. ADSL2+. 8 ADSL ADSL2. 1 Km 2 Km 3 Km 4 Km 5 Km 6 Km Length, Km Source: Ericsson Passive Optical Networks ADSL: User Devices Splitter separates data from voice signals Modem (de)modudulates signals Voice Data at proper frequencies ( , in ADSL, from 25 KHz in upstream, and from 240. KHz in downstream). Passive Optical Networks HFC Access network CATV infrastructures are also called Hybrid Fiber Coax (HFC). tap Head Remote node amplifiers end fiber coax They offer a unidirectional high speed downstream channel Passive Optical Networks Fiber To The X (FTTx). Service Node Internet $$$. Optical Fiber ONT FTTH Later . Leased Line $ ONT FTTB Soon . Frame/Cell Relay OLT.

3 $$. Telephone ONU NT FTTC Later . Twisted Pair $-$$. Interactive Video ONU NT FTTCab Soon . PON xDSL. FTTH : Fiber To The Home FTTC : Fiber To The Curb FTTB : Fiber To The Building FTTCab : Fiber To The Cabinet Passive Optical Networks Optical Access Networks Low Attenuation, large Requires new fiber distances installation Low power consumption Outside plant costs are Large Bandwidth, many important!! broadband users Passive Optical Networks Optical Access Networks Point-to-Point links Simple, standardized and mature technology N fibers lines 2N transcievers Passive Optical Networks Optical Access Networks Active Optical network Simple, standardized and mature technology 1 fiber line Curb Switch power in the field 2N+2 transcievers Passive Optical Networks Optical Access Networks Passive Optical network (PON). Simple, under standardization technology 1 fiber line N+1 transcievers Passive devices (splitters). Passive Optical Networks PON Overview OLT: Optical Line Terminator ONU: Optical network Unit ODN: Optical Distribution network c fi f r a T.

4 A m r e s t n ow Tr a ffic D a m Upstre Passiv e Device s ODN. Passive Optical Networks Time 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 WDMA. Time Division Multiple Wavelength Division Multiple Access Access Passive Optical Networks PON 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.

5 Passive Optical Networks Contents Introduction Motivation 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 TDM-PONs Passive Optical Networks Passive Optical Networks PON Physical Layer Passive splitter/combiner(s). Two separated channels Downstream (OLT ONUs). Upstream (ONUs OLT). A 3rd channel can be used for broadcasting video ODN ONU. OLT ONU. Passive Splitter ONU. Passive Optical Networks Optical Fiber: Attenuation Single Mode Fiber (SMF) to achieve large distances ITU SMF (STD). water peak attenuation renders the 1360nm 1480nm spectrum unusable for data transmission ITU G652c/d SMF (ZWP). zero-water peak . First STD SMF. Window Second Window ZWP. SMF. ATTENUATION (dB/km). Third 850nm 1310nm Window 1550nm 800 900 1000 1100 1200 1300 1400 1500 1600 1700. WAVELENGTH (nm). Passive Optical Networks Optical Fiber: Chromatic Dispersion Causes signal pulse broadening Passive Optical Networks Wavelengths Low loss ( dB/km).

6 1310nm Zero chromatic dispersion Low loss ( dB/km). 1490nm Chromatic dispersion ( 10-17 ). 1550nm Optically amplified by EDFAs (1550nm). Passive Optical Networks Lasers Diodes (LD). Simple FP. Fabry-Perot (FP) +. gain Cheap Noisy mirror cleave . - Sensitive to chromatic dispersion Used on 1310 nm DFB. +. Distributed Feedback (DFB) gain More expensive mirror AR coating . Narrow spectral width - Less sensitive to chromatic dispersion Used on 1550 nm (or 1310 nm). Passive Optical Networks Photodiodes (PD). PIN Photodiodes Good Optical sensitivity ( -22 dBm). Silicon for shorter 's (eg 850nm). InGaAs for longer '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 Passive Optical Networks Typical PON Configuration Wavelengths Dual Fiber 1310nm. Upstream on 1310nm Single Fiber Downstream on 1490nm Transceivers Upstream Downstream ONU FP PIN. OLT APD DFB. Passive Optical Networks Downstream Traffic Downstream traffic is broadcasted to all ONUs Weak security ONUs filter data (frames) by destintation address ONU.

7 OLT ONU. Passive Splitter ONU. Passive Optical Networks Downstream Traffic Scheduling OLT schedules traffic inside timeslots Time Division Multiplexing (TDM) scheme Time slots can vary from s to ms B A. C. B. A. A B C B. A B C B. OLT B. Passive A. Splitter B. C. B. C. Passive Optical Networks Downstream Frame Reception Each ONU receives all the frames with the same constant power Simple receiver (low-cost) @ ONUs Frames have preambles/markers A. 7. km OLT B. 3. km 1. C. km Passive Optical Networks Upstream Traffic All ONUs share the same upstream channel ONUs cannot exchange data directly Collisions may occur at the splitter/combiner ONU. OLT ONU. Passive Splitter ONU. Passive Optical Networks Upstream 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.). Collision!! A. A. B B. A C B B. OLT B. Passive C. Splitter C. Passive Optical Networks Upstream Traffic Scheduling 2/4.

8 In general, PON standards propose Time Division Multiplexing Access (TDMA) schemes Upstream time slicing and assignment A. A. A B C B. B B. OLT B. Passive Splitter C. C. Passive Optical Networks Upstream Traffic Scheduling 3/4. Typically, downstream traffic carries grants that schedule upstream traffic Grant distribution must take into account the different propagation times to reach each ONU. 1 B A. C 10 km 2 B. 2 1 A 2 1. A B C B. A B C B. OLT B. Passive A. Splitter 2 B. C. 1 B. C. 2 km Passive Optical Networks Upstream Traffic Scheduling 4/4. 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. A. A 10 km C A. OLT B. Passive Splitter C. C. 1. C. 2 km Passive Optical Networks Upstream Frame Reception The OLT receives frames with different powers Much difficult to recover synchronism Burst Mode Receiver (complex) @ OLT.

9 Sets 0-1 threshold on a burst basis A. A. 7. km B A B. OLT B. 3. Passive km Splitter 1. C. km Passive Optical Networks Power 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 Conventional Low-loss Connection dB dB. Splices dB dB. Fiber (1310nm) dB/km dB/km Fiber (1490/1550nm) dB/km dB/km Passive Optical Networks Passive Splitters 1x2 Splitter 1xN Splitter Every time the signal is split two ways, the signal is reduced by 10log( )=3dB. Loss 3dB log2(#ONUs). Conventional Low-loss Splitter 1x2 Passive Optical Networks Splitter/Couplers Configurations 4-stage 8x8 3-stage 8x8. Passive Optical Networks Transceiver Assumptions TX Power RX Sensitivity ONU (FP+PIN) 0 dBm -22 dBm OLT (DFB+APD) 1 dBm -30 dBm Upstream (@1310nm) Power Budget = 30 dB. Downstream (@1490nm) Power Budget = 22 dB. Passive Optical Networks Video Distribution over PONs Video can be distributed in several ways RF video signal (overlay video).

10 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 Passive Optical Networks RF Video Signal 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. vide o ONU. EDFA. vide o OLT ONU. Passive vide Splitter o ONU. vide o Passive Optical Networks RF 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.