Fiber Optic Transmission Systems. Professor Roberto Gaudino Politecnico di Torino, Italy

Transcription

1 Fiber Optic Transmission Systems Professor Roberto Gaudino Politecnico di Torino, Italy

2 Sample slides from the CEI-Europe course: Fiber Optic Transmission Systems Roberto Gaudino, Politecnico di Torino, Italy Optical Access Networks 2

3 Classification of public networks Submarine Network Central Office (CO) Local Access Network Last Mile : From the user to the nearest central office Metropolitan Local-exchange Network Connections among closely located central offices inside a city Long Haul Interexchange Network, or Core Network (national and international) 3 Access Networks today (2012) For access network we mean the last part of the public network toward the final user, which can be further divided into two very different areas: Business Residential These networks are usually owned and managed by big national telecom operators 4

4 POTS: Plain Old Telephone Service TYPICAL DISTANCES: from 300m to 3000 m Central Office Bundles of twisted pair cables (up to some thousands) Street Cabinet Smaller bundles (up to some hundreds) Street Cabinet Street Cabinet 5 Twisted pair cablings A picture taken in a central office 1.6

5 Optical Solutions: FTTx CO The key idea: use a fiber going as close as possible to the final user ONU = Optical Acronyms Fiber Network Unit ONU Copper, twisted pair NIU NIU = Network Interface Unit FTTCab Fiber to the cabinet CO ONU Copper, twisted pair NIU FTTB Fiber to the Building CO Central office ONU/NIU FTTH Fiber to the Home 7 FTTx and bit rates Central Office Primary Cabinet Secondary Building ( m) ( m) FTTE xdsl ADSL Mbps <1 Mbps FTTCab ONU VDSL2 VDSL2 17M M 2-10 M FTTB VDSL2 30M M M FTTH Optical Gbps ( unlimited ) 8

6 Pros and cons of FTTH solutions PROs: It solves any reasonable bandwidth limitation Significantly longer distances, if needed CONs: It requires a complete re-cabling of the residential access networks Very high CAPEX costs (CAPital Expenditures, i.e., initial investments) A new optical modem in each apartment The estimate cost to reach a new user in FTTH are of the order of 1k per user, most of which related to digging and civil engineering In the end, the most critical/expensive part is re-cabling existing buildings 9 Intentionally left blank Copyright 2011 R. Gaudino, Optical Communication Group, Politecnico di Torino 10

7 Two main options for FTTx: P2P and PON 11 Two different options for FTTx A dedicated fiber for each optical end-point It is sometimes indicated as Peer-to-Peer o Point-to- Point (P2P) Typical for FTTCab or FTTB It is used anyway also in some countries for FTTH A shared optical infrastructure for many users PON: Passive Optical Networks 12

8 P2P Architecture Dedicated fiber pairs from the central office to the residential user O/E Central Office OLT (Optical Line Terminal) O/E O/E ONU (Optical Network Unit) 13 PON: Passive Optical Network Central Office Passive Optical Splitters O/E O/E OLT (Optical Line Terminal) O/E ONU (Optical Key points: Network Unit) Bidirectional transmission over a single fiber running out of the central office Optical splitter to reach N users In some situation, there may be two levels of splitting: first in the street cabinets, then in the building basement 14

9 P2P vs PON P2P advantages Very simple and inexpensive optical transceivers at both sides of the link Virtually unlimited bandwidth Unbundling is possible at the very physical layer by moving a fiber in a patch panel (just as in POTS) PON advantages Lower cost in the cable installations A much smaller number of terminations (optical transceivers) in the central office Possibility of statistical multiplexing among many users Reduced power consumption Reduced footprint (dimensions) 15 Passive Optical Networks (PON) Roberto Gaudino 16

10 PON Overview and Acronyns OLT: Optical Line Terminato ONU: Optical Network Unit ODN: Optical Distribution Network Passive Devices ODN 17 PON Standards Working Groups Full Service Access Network (FSAN) Group Ethernet in the First Mile (EFM) Alliance Propose standards Standards Bodies International Telecommunication Union (ITU-T) Institute of Electrical & Electronics Engineers (IEEE) 1998/2001 Standards APON/BPON 2003 (G.983) GPON (G.984) 2010 XGPON (G.987) Ratify standards 2004 EPON (802.3ah) GEPON 802.3av 18

11 RF Video Signal (overlay) A 3 rd channel (1550nm) is used in some PON architectures for video distribution in downstream Particularly in countries that have a widespread CATV GPON GPON (downstream) Proper WDM filters (usually called triplexers ) are needed at the OLT and ONU to separate the three wavelengths 19 The current most advanced (but fully released) standards: FSAN/ITU: XGPON IEEE: 10GEPON 20

12 XG-PON and 10G-EPON ITU-T has recently released (January 2011) its Recommendations G and G on XG- PON. Main features: 10 Gbit/s downstream 2.5 Gbit/s upstream Up to 40 km reach Up to 35 db power budget Similar specs have been approved by IEEE for 10G- EPON in September 2009 (802.3av) 21 XG-PON and 10G-EPON These two standards are very similar to GPON, except for the increase in bit rate So they are still based on: Single wavelength transmission for each direction TDM/TDMA multiplexing Pure binary On-Off IM-DD, no fancy modulation or equalization Anyway, to achieve a high power budget, the following techniques are already included in the standards: Simple FEC (Reed-Solomon) APD or SOA at the receivers to increase sensitivity 22

13 Wavelength allocation WDM1r ports NGA OLT OLT OTDR EPON 10G EPON (10GE) 10GE EPON US US 10GE DS GPON XG-PON1 (XG1) XG1 US GPON US GPON DS Video XG1 DS nm Please note that to allow backward compatibility with GPON+video overlay, some unusual wavelengths have been selected 23 GPON and XGPON Coexistance From ITU-T G.987 Reccomendation 24

14 The future: NG-PON2 25 Next-generation PON (NG-PON2) Starting in 2010, FSAN started to work on defining what should come after XG-PON A working group has been set inside FSAN The following slides show what has been proposed so far in FSAN and in the related literature, but no final decision was taken yet For more info, please see: 26

15 Next-generation PON (NG-PON2) The FSAN NG-PON2 general targets are: Increase the reach to Km (or more) Increase the splitting ratio up to 256 users (or more) Increase the effective bit-rate per users (in both directions) to a value closer to 1 Gbit/s per user Additional requirements (still under debate) No optical amplification in the ODN No optical filters in the ODN None of this goals are possible without significantly changing the transmission technologies Pure binary On-Off IM-DD seems out of question 27 NG-PON2 timeframe FSAN is working on a white paper on NG-PON2 No public version available yet (end of 2011) The time frame for an actual deployment may be fairly long (2015 or later) Remember that XG-PON is not yet deployed 28