From TDMA to WDM-PONSjur FredriksenAril Schultzen

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

Architecture summary

Source: “PON in Adolescence: From TDMA to WDM-PON”, page 31

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

Structure today

Source: “PON in Adolescence: From TDMA to WDM-PON”, page 33

Structure of tomorrow

Source: “PON in Adolescence: From TDMA to WDM-PON”, page 33

Conclusion

● Next step PONs are WDM-PONs with TDMA techniques● Higher reach, splitting ratios and bandwidth than GPON/EPON● Supports various fiber topologies● Enables evolution to unified access and backhaul● Combination with DWDM and TDMA to optimize cost