WDM Passive Optical Networks Protection and Restoration

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					     OECC 2009 Workshop: Next-generation Broadband Optical Access – Future Challenges
     Session 1: Broadband Network Architectures, WDM PON Evolution Strategies and Future
                Ultra-high- bandwidth Services


                       WDM Passive Optical Networks:
                         Protection and Restoration

                                      Calvin C K CHAN

                              Lightwave Communications Laboratory
                              Department of Information Engineering
                               The Chinese University of Hong Kong
                                         HONG KONG


                                                        Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                 P.1
                                                         The Chinese University of Hong Kong
            Network Survivability in PONs

           Conventional PONs have limited protection features to keep the
           cost low.


           The traffic on PONs is getting more data-centric. Subscribers are
           requesting high-availability services and connections.



           need to provide resilience against failures due to catastrophic
           events like fires, flooding, earthquakes, etc.




                                                    Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                             P.2
                                                     The Chinese University of Hong Kong
            Network Survivability in PONs
            Fault Management in optical networks
            Conventional approach: diagnosis on high layers
               based on status reports collected from various checkpoints on the
               managed optical network
               incurred overhead in network signaling and network management system
               no guarantee that higher layers could provide recovery from faults in the
               physical layer.


               Network protection in optical layer
                   simple fiber link or equipment duplication with protection
                   switching or some other intelligent schemes with minimal
                   resource duplication
                   faster response



                                                         Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                  P.3
                                                          The Chinese University of Hong Kong
            Network Survivability in PONs

            For PONs
               Equipment failures at either OLT or ONU
                        having a backup unit in a controlled environment.
               Fiber cut
                        takes a relatively long time to perform the repair



               Survivable network architectures for PONs with protection
               switching is highly desirable to bypass the failed fiber links and
               re-route the affected traffic.




                                                        Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                 P.4
                                                         The Chinese University of Hong Kong
            Survivable WDM-PONs
            Design Consideration: Protection / Restoration

       Protection                                     Restoration
       Protection lightpaths are pre-planned          Dynamically search for spare
       at the network design stage.                   lightpaths to restore the disrupted
                                                      traffic after network failure.
       Low traffic restoration time                   Maybe long traffic restoration time
         only protection switching is needed to          depending on the dynamic re-routing
         enable the protection lightpath.                of the disrupted traffic, and the routing
                                                         decision computation.

          For WDM-PONs, topology is regular (tree / ring)
              Preplanned protection
              Protection on optical layer         further reduce the traffic restoration time
              Minimize the disturbance to the higher layers
                                                               Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                        P.5
                                                                The Chinese University of Hong Kong
             Survivable WDM-PONs
      Design Consideration: Wavelength Routing
      In addition to lightpath diversity with fiber link duplication and switching,
      WDM-PONs offer one more dimension (Wavelength)
         wavelength routing
            may reduce the amount of resource duplication

      Design Consideration: Network Topology
      Network topology determines the paths or connections between the OLT
      and the ONUs
         influences how the protection lightpaths or fibers be duplicated or incorporated

      Tree topology:      feeder fibers, distribution fibers
      Ring topology:      dual fiber ring, or single fiber ring with uni-/bi-directional
                          OADM in each network node

                                                               Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                        P.6
                                                                The Chinese University of Hong Kong
             Survivable WDM-PONs

      Design Consideration: Single / Multiple Failures
       Mostly consider single failure at a time
          the occurrence of a fiber or equipment failure is statistically independent in a network.
          mean time between failures is generally much longer than the mean time to repair a
          failure
       Protection against multiple failure scenarios has also been investigated recently.

      Design Consideration: Automatic Protection Switching (APS)
      Centralized control      all APS at OLT
                               better APS management
                               requires monitoring and collection of fault alarms throughout the network
      Distributed control      APS at individual ONUs,
                               requires protection switches at the ONUs, transparent to OLT
                               ONU only monitors the status of its attached fibers
                                increases the complexity and cost of ONUs
                                                                Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                         P.7
                                                                 The Chinese University of Hong Kong
            Survivable WDM-PONs
         Design Consideration: Fault Monitoring
         Fault monitoring units have to be installed at strategic checkpoints to gather
         the network status information
                 Can be as simple as mere optical power level monitoring (loss of signal) or
                 presence of a particular wavelength, etc.
         Collected monitoring information has to be delivered to APS units for
         appropriate remedies, a signaling channel may be needed in some cases.

        Design Consideration: Traffic Restoration Time
        Time period between when the failure is detected and when the affected traffic
        is restored.
            should be kept small, say a few tens of milliseconds
            depends on:
                  the intrinsic response of the optoelectronic detection and the optical switching
                  devices used in APS,
                  possible induced additional latency of the protection lightpath

                                                              Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                       P.8
                                                               The Chinese University of Hong Kong
            Protection Architectures for PONs
            ITU-T G.983.1
                                 ONU#1                       ONU#1
                            RN                          RN
             OLT                         OLT


                                 ONU#N                       ONU#N



                      (a)                         (b)

                                 ONU#1                       ONU#1
                            RN                    RN


             OLT                         OLT



                                 ONU#N                       ONU#N



                      (c)                        (d)
                                                                     optical line interface/
                                                                     optical transceiver

                                               Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                        P.9
                                                The Chinese University of Hong Kong
                      Group Protection Architecture
                                                            OLT

                                                                         Down- & Upstream Wavelengths for ONU1
                                                                         Down- & Upstream Wavelengths for ONU2


                                                           1×N AWG                               RN
  WC : WDM coupler



   Group 1                                                                                                                          Group i

              Blue/Red filter     Blue/Red filter                              Blue/Red filter                   Blue/Red filter




             WC                               WC                            WC                                              WC
       PD      LD                          PD       LD                   PD     LD     ONU(2i-1)               ONU(2i)   PD        LD
       Data router                        Data router                    Data router
                         ONU1   ONU2                                                                                     Data router



    LAN / subscribers                  LAN / subscribers                LAN / subscribers                              LAN / subscribers
                                                              T. J. Chan et al., “A self-protected architecture for wavelength division
                                                              multiplexed passive optical networks,” IEEE Photonics Technology
                                                                            15, no. 11, pp. Communications
                                                              Letters, vol. Lightwave 1660-1662, Nov. 2003. Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                                   P.10
                                                                            The Chinese University of Hong Kong
                 Remote Node Duplication




    E. S. Son et al, “Survivable network architectures for WDM PON”, OFC/NFOEC’05, Paper OFI4, Anaheim, California, USA, 2005.

                                                                                    Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                                            P.11
                                                                                     The Chinese University of Hong Kong
                 RN Duplication




    E. S. Son et al, “Survivable network architectures for WDM PON”, OFC/NFOEC’05, Paper OFI4, Anaheim, California, USA, 2005.

                                                                                    Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                                            P.12
                                                                                     The Chinese University of Hong Kong
                 Using N×N AWG at RN




     K. Lee, S. G. Mun, C. H. Lee, and S. B. Lee, “Reliable wavelength-division-multiplexed passive optical network using novel
     protection scheme,” IEEE Photon. Technol. Lett., vol. 20, No. 9, pp. 679-701, 2008.

                                                                                        Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                                                P.13
                                                                                         The Chinese University of Hong Kong
                 Survivable Single-Fiber Access Ring


          Tx1d    Rx1u     Tx2d    Rx2u    Tx3d    Rx3u    Tx4d    Rx4u       From AN3                                       To AN1
        λ 1d     λ1u     λ 2d     λ2u     λ3d     λ3u     λ4d     λ4u
                                CWDM MUX/DMUX
                                                                                                             Optical
                                                                        Hub                                  Switch


                                                                                          Drop λ 2                 Add λ 2
                                                                  Upstream
                           AN4                     AN1                               1     2                 1     2
                                                                                           3                       3
                                                                                                                             CWDM
                                                                                                       Control               OADM
                                                                                                       Circuit
                                                                Downstream
                                                                                         Rx2d   λ 2d             Tx2u   λ 2u
                           AN3                     AN2


                                                                                                       AN2



        Z. X. Wang et al., “Demonstration of a single-fiber self-healing CWDM metro access ring network with uni-directional OADM,”
        IEEE Photonics Technology Letters, vol. 18, no. 1, Jan. 2006.


                                                                                    Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                                            P.14
                                                                                     The Chinese University of Hong Kong
            Issues

   •   For evaluation of various feasible survivable network architectures, here
       are some issues to consider / compare
          Degree of Protection: feeder fiber, and/or distribution fibers, and/or WDM
          router at remote node, and/or ONUs, and/or transceivers at OLT, etc.
          Network Availability
          Ease of management and control (at OLT or ONU)
          Amount of duplicated and additional fibers/components         cost / complexity
          Intrusiveness to the other in-service traffic
          Traffic restoration time
          Practical issues, such as availability of laid fiber, power consumption, etc.



                                                          Lightwave Communications Laboratory
 OECC2009 Hong Technologies
Optical Access NetworkKong                                                                  P.15
                                                           The Chinese University of Hong Kong

				
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