Post on 31-Aug-2018
transcript
Intro
● “PON in Adolescence: From TDMA to WDM-PON”
Grobe, Klaus et al.;
IEEE Applications & Practice: Topics in optical communications
January 2008, Pages: 26-34
● Many proposals for WDM-PONs○ Cost and performance are important aspects for success
○ bandwidth per user, splitting ratio and maximum reach
● The article used as source is analysing these proposals
● Heavy subject, we’ll try to go easy on you
Preliminary Knowledge
● OLT = Optical Line Termination (central)
● ONU = Optical Network Unit (end-user)
● Power Budget = budgeted loss○ Fiber attenuation
○ Couplers
○ Splicers
○ Connectors
○ Muxes/demuxes
TDMA
● Time Division Multiple Access
● Multiple signals over the same frequency / wavelength
● Uses time-slots
TimeslotsFrequency
TimeSource: www.wirelesscommunication.nl/reference/chaptr04/multi/tdma.htm
WDM
● Wavelength-Division Multiplexing
● One fiber = multiple wavelengths (wl)
● Multiple wl = broader bandwidth
● Separation gives better security
● Cost effective upgrade
● Better usage of available fiber
● More often used with amplifiers than TDMA
Source: WDM operating principle.svg By Xens (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
GPON (ITU-T G.984)
● Gigabit PON
● Popular in Europe and North America○ In Norway: Telenor / Canal Digital / Get
● High bandwidth efficiency
● Lower build cost because better fiber utilization
● Supports IP, ATM and TDM payloads
● Uses TDMA
EPON (IEEE802.3ab)
● Ethernet PON
● Popular in Japan and Korea
● Lower bandwidth efficiency compared to GPON (less payload)
● Natively supports Ethernet
● Integrated into Ethernet in the First Mile (EFM) and Operation, administration
and maintenance (OAM) approach
● Uses TDMA
GPON vs EPON
*Table shows costs normalized with respect to GPON.
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 27
Next Generation of PONs
● TDMA based PON can’t cope with future bandwidth needs
● Use of passive splitters imposes loss○ limits attainable link lengths
● These problems can be mitigated with WDM PONs○ enhanced privacy
○ enhanced bandwidth
○ can be combined with TDMA based PON
● Next up, some architectures.
Splitter WDM-PON
● DS Wavelengths are broadcasted● Passive splitter (attenuation)● Individual ONUs with individual wl (DS/US)
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
AWG● Arrayed Waveguide Gratings
● Optical (de)multiplexers in WDM systems
● Light waves of different length interfere linearly with each other
Source: Arrayed-Waveguide-Grating.svg By Dr. Schorsch (self made illustration.) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
AWG-based wavelength routing PON
● DS Wavelengths are broadcasted● AWG router instead of splitter (lower attenuation)● Simpler ONUs, still need for different TX wavelengths
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
Wavelength routing with spectrum sliced LED
● Broadcasted DS wavelength● Identical ONU design with common US (AWG slices)● LED suffers from poor power budget in SM fiber● Limited US bandwidth
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
Colorless ONUs for single fiber (RSOA/REAM/IL-FP)
● Colorless ONUs reduces cost● Single fiber reduces cost● Dedicated seed, limited number of ONUs
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
Colorless ONU using FSK/OOK with RSOA in ONU
● Reuse OLT TX in ONU for TX data● Constant Envelope signal must be used in OLT (FSK)● FSK removed and OOK used in US
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
Simple CWDM PON based on CWDM SFP
● Another type of mux/demux - Thin-film filters● CWDM SFPs to use different wavelengths● Low cost transceivers, but more expensive ONUs● Requires low water-peak fibers to support all channels
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
WDM-PON Application
● Extend range● Higher bandwidth● Higher splitting ratios
○ (above 1:100) amplification is needed
Because of all these factors it can be used in unified metro and backhaul networks