Optical Networks, Current and Future Technologies for WDM By: Bogdan Ionescu

1. Optical Networks, Current and Future Technologies for WDM By: Bogdan Ionescu DSRG, University of Ottawa July 5, 2000

2. Purpose • Introduction to WDM • Current Technology Standpoint • WDM Network Topologies and Architectures • Failure Resiliency • Switching and Routing • QoS in WDM • Access Networks • SONET and WDM • Control Plane for WDM Networks • Direction of WDM Networks • Conclusion

3. 1. Purpose • Board study of WDM technology • Deployment • Work in progress • Establish future research areas in WDM

4. 2. Introduction • Current optical signals • have least signal loss around the region of 1300 or 1500 nm • SONET use only one of these wavelengths at a time • WDM applies same principles as FDM to the optical domain • many optical signals • each with their own wavelength (carrier freq.) • placed onto one fiber

5. 2. Introduction • How WDM works? • advances in optical components allow a window of wavelengths around the 1300 or 1500nm thresholds • with latest lab technologies • window size of 100 wavelengths • for OC-192 (9953.28 Mb/s) => 1 Tb/s • this is DWDM • e.g. of such optical components [1]: • Distributed Feedback Lasers (DFB) • Erbium-doped Fiber Amplifiers (EDFA’s) • Photo-detectors • Multi-frequency Lasers

6. 2. Introduction • Optical Components for WDM [1] • Important Parameters: • Tuning Time: time required for a laser/filter to focus on a particular wavelength • Tuning Range: spectral window, i.e. how many wavelengths

7. 2. Introduction • Properties of tunable lasers [1]

8. 2. Introduction • Characteristics of tunable filters [1]

9. 2. Introduction • (WDM Network Components) • Optical Add/Drop Modules (OADM) • signal grooming and splitting • usually made of Arrayed-Waveguide Gratings (AWG) or Fiber Bragg Gratings (FBG) •  Crossconnect (WXC) • key component in constructing networks • composed of: • Mux, Dmux, switches,  Crossconnect

10. 2. Introduction • (WDM Network Components) • Reconfigurable  routing switches • a) employing  converters b) employing photonic switches

11. 3. Current Technology Standpoint • Today WDM technology is mainly deployed for increasing “pipe” capacity of backbone networks. • SONET interfaced with WDM Mux/Dmux • used for point-to-point connections • up to 100 times the wavelengths over same optical fiber • no need to lay new fiber for multiplied capacity on backbone trunks • no known deployment of switching out routing WDM (in development only) • WDM Mux/Dmux simple device requires minimal control mechanisms for focusing lasers and filters.

12. 4. WDM Network Topologies and Architectures • Broadcast and Select [1] • sender relays information to all other nodes • receiver node selects information of interest by use of “enabling technology) • e.g. a tunable filter to select the  carrying info. • tunable transmitters (TT), tunable receivers (TR), • fixed transmitters (FT), fixed receivers (FR) • Topologies • star coupler, (N/2)log2N individual couplers • bus, 2N couplers, high signal loss • ring, high power dissipation better failure-resilience • MAC protocols needed

13. 4. WDM Network Topologies and Architectures • Broadcast and Select Topologies [1]

14. 4. WDM Network Topologies and Architectures • Broadcast and Select demonstrators: [1] • LAMBDANET [16-20] late 80’s and early 90’s, one of first, built by Bell Core • 18  separated by 2nm & modulated @ 1.5 Gb/s over 57 km • RAINBOW I & II [1] in the early 90’s by IBM • 32  separated by 1nm giving 300 Mb/s in I and 1Gb/s in II • Other: • STARNET I &II by Stanford University • European Research and Development for Advanced Communications in Europe (RACE)

15. 4. WDM Network Topologies and Architectures •  Routing Networks [15,17] • information is routed, switched and forwarded based on  • therefore obtain a physical and logical topology •  reuse throughout network => increased capacity • currently 4 to 32  networks exist and expected to increase to 100 (DWDM) [15] • virtual topology gives an optical layer to serve higher layers e.g. offering VPN’s • issues to consider: • transparency, reliability,  reuse, virtual topology, static/dynamic routing  assignment (RWA) [15,17,18]

16. 4. WDM Network Topologies and Architectures •  Routing Networks

17. 4. WDM Network Topologies and Architectures •  Routing Networks demonstrators [1] • Multiwavelength Optical Network (MONET) program • developed by Bellcore funded by DARPA [18,19] • uses 8  spaced by 200 GHz & modulated @ 2.5 Gb/s, in a ring topology • latest demonstrators gave 10 Gb/s for 2000 km • All-Optical Network (AON) between MIT and DCE [20] • uses 20  spaced by 50 GHz (0.4nm) • Multiwavelength Transport Network by RACE [18] • uses 4  spaced by 500 GHz & modulated @ 622 Mb/s or 2.5 Gb/s • Other: WSAPNET, OPEN, MOSAIC, OPERA [18,16]

18. 4. WDM Network Topologies and Architectures • WDM Ring [5] • conceptually similar to a SONET ring • main difference is in failure-resiliency • Wavelength Cross Connect (WXC) interconnected in a ring topology • WXC use  switching and conversion • allows for better service protection than SONET •  (lightpath) protection in addition to path and line protection. • i.e. laser failure is fixed by converting , no need for rerouting => faster recovery • flexible and higher routing capacities • [8] identifies eight types of WDM rings • [25] studies several failure-resilient WDM rings

19. 4. WDM Network Topologies and Architectures • WDM Mesh Networks [5] • same optical components as for WDM rings i.e. WXC’s • protocols are more complex • failure-resiliency [9] • routing &  assignment [10] • likely to be used for backbone infrastructures

20. 4. WDM Network Topologies and Architectures • Example of interconnected WDM network infrastructure; Mesh, Ring, and Access ( Discussed Later )

21. 5. Failure Resiliency • (Currently in SONET) • SONET/SDH survivable architectures [1] • Automatic Protection Switch (APS) protocol • protects against fiber cuts by automatically redirecting traffic • 1+1 protection: • same signal is transmitted through two non-intersecting paths • destination decides on which signal to choose • 1:1 protection: • two non intersecting paths; working and reserved • reserved path is idle or used by low priority traffic in “non-breakdown” times

22. 5. Failure Resiliency • (Currently in WDM ) • WDM networks will likely mirror SONET/SDH survivable architectures. • Two type of classifications [11-14] • Protection • protection resource are reserved ahead of time • protection resource may be used by low priority trafficat “non-breakdown” times • Restoration • alternate routes of spare resources are discovered at failure detection time • if discovery of alternates fails, data is lost • better resource utilization at “non-breakdown times” • slower than protection scheme (reconfig.. path)

23. 5. Failure Resiliency • (Currently in WDM ) • Two main schemes extensively implemented • First scheme: Fiber Protection Switching • applied to point-to-point and ring architectures • working fiber is backed up by another disjointed fiber • entire fiber is switched • granularity of one fiber

24. 5. Failure Resiliency • (Currently in WDM ) • Second scheme: At the Wavelength Level [6] • applied to cross-connected mesh architectures • slower but more bandwidth efficient • Three variants: • link • fastest failure detection • recovery is local to one point (i.e. @ link level) • path • reroutes between two end nodes • full advantage of network spare capacity • slower to detect and recover • disjoint-link path • at path setup time, an alternate path is selected as well • traffic restored immediately

25. 5. Failure Resiliency • (IP over WDM) • For IP over WDM/DWDM • abolishes current architecture • IP over ATM over SONET over WDM • functional overlap • slow to scale • failure resiliency at different layer may interfere with each other and provide network instability

26. 5. Failure Resiliency • (IP over WDM) • Detection and restoration at different layers

27. 5. Failure Resiliency • (IP over WDM) • Proposed joint protection/restoration scheme coordinated at both IP and WDM layers [6] • needs traffic engineering for WDM networks • Optical control framework needed at optical layer • Key is combining [21]: • recent advances in IP-MPLS-based control plane constructs • with OXC technology • this is proposed by MPS [21] • sharing of information between IP & WDM layers • IP to directly access WDM channels

28. 5. Failure Resiliency • (IP over WDM) • Proposed architecture for MPLS-basedtraffic engineering [6] • automatic topology discovery • OXC to dynamically learn networks • no manual intervention • state information dissemination • extension to link-state routing, e.g. OSPF • link attributes added to state tables and advertisement • max. available link BW • max. reservable link BW • current BW reservation • current BW usage

29. 5. Failure Resiliency • (IP over WDM) • path selection • RWA problem • which LSP (Label Switched Path) to choose for required  QoS values • choose a centralized or distributedalgorithm • path management • establish, maintain, tear-downof LSP • use of signaling protocols such as • RSVP • CR-LDP (Constraint-Based Routed Label Distributed Protocol) • This allows for Joint Protection/Restoration at the IP/WDM Layers

30. 6. Switching and Routing • Have seen so far the physical and control mechanisms required for switching / routing in WDM networks • Primary problem: Contention Resolution • Contention in WDM : when packets are switched and two or more packets trying to leave the same port on the same  • Three types of contention resolution mechanisms [4]: • optical buffering • deflection routing •  conversion

31. 6. Switching and Routing • Optical Buffering (deflection in time) [4] • delay lines • fixed fiber lines each giving pre-calculated delays • delays in term of packet durations: 1,2,3 ..., m • packet sent directly to output or to required delay line based on required delay • recirculation fiber loops • based on fiber loop delay line with multiple  channels • at contention, packet is converted to  available in the loop • kept circulating by corresponding passive fixed filter • converted to  available at output when contention is resolved • both suffer from increased signal to noise ratios

32. 6. Switching and Routing • Deflection Routing (deflection in space) [4] • one packet routed along desired “minimum distance-routing” link • others are forwarded to greater than “minimum distance-routing” links • (optical buffer may still be used here) • source-destination pair routes are no longer fixed, i.e. different routes possible as in IP • parameters that affect performance of deflection routing • network diameter (max. # of hops) • deflection cost (increase in hops) • problems similar to IP routing can arise esp. in asynchronous transmission networks • wondering packets, throughput collapse

33. 6. Switching and Routing •  Conversion(deflection in  domain) [4] • convert additional packets to a different  following the same next hop link as original packet • needs mechanism for choosing alternate  but on same output fiber • best results were obtained if combined with buffering • reduced probability of signal loss in buffering

34. 6. Switching and Routing • General Comparison • Buffering • better network throughput at higher hardware and control cost • Deflection Routing • easier to implement, cannot offer ideal network performance •  Conversion • in-between with less signal loss

35. 7. QoS in WDM • Differentiated Optical Services (DoS) [2] • Provide Classes of Optical Services (DiffServ)based on: • lightpath characteristics • jitter •  wander • crosstalk • amplified spontaneous emission • available failure-resiliency characteristics • protection • restoration • signal regeneration • 3R, retiming and reshaping (signal dependant), non-transparent but re-clocking • 2R, regeneration, no retiming => jitter • 1R no retiming and reshaping, simplest and most transparent to optical format

36. 7. QoS in WDM • DoS set of parameters characterize quality and impairments of optical link • quantitative: delay, jitter, BER, BW • functional: monitoring, protection, security • Need for Classification and Mapping of Optical Service • grouping OCh into classes reflecting previous QoS parameters • mapping aggregate DiffServ flows into corresponding OCh grouping • admission ctrl. and policing to ensure that ingress DiffServ flows do not exhaust available optical resources • Architecture involves edge-devices performing the above functions with a simple WDM core • Need for monitoring & control plane to core devices

37. 7. QoS in WDM • E.G. : Optical Service Classification

38. 7. QoS in WDM • General Mechanisms to enforce QoS: • optical buffering according to priorities/classes • deflection routing according to priorities/classes •  conversion according to priorities/classes • MPLS/OSPF/RSVP • Monitoring by way of: • OADM’s (Optical Add /Drop Modules • or opto-electric-opto conversion

39. 8. Access Networks • Passive Optical Networks (PON) [5] • placed at WDM Ring access level • a bus or star topology • medium access protocol (MAC) coordinates transmission amongst users • are less expensive than WDM rings due to lack of active components • SONET rings • Room for QoS here as well: • Dynamic Resource Allocation for Quality of Service on a PON with Home networks [7]

40. 8. Access Networks • Example of current Access Networks for WDM

41. 9. SONET and WDM • 10 years to finish migration to SONET [5] • Large investment made in SONET equipment • North American Total as of 1998, $4.5 billion • For WDM to be accepted readily it has to integrate/be backward compatible with SONET • Optical Transport Networks (OTN) [1] • switched/routed WDM networks (OC-48 to OC-192) • composed of WXC nodes • control system for setup and teardown of lightpaths, monitoring, and fault recovery • needs definition of frame format (currently being defined [22]) • OCh frame format to borrow SONET concepts

42. 9. SONET and WDM • SONET Frame must be easily encapsulated into OCh frame • e.g. OC-48 SONET frame cannot fit in an OCh payload at OC-48 due to required OCh overhead bytes. • Some WDM equipment must have physical SONET interfaces as specified in [23] • SONET side need not be aware of WDM • WDM equipment might have to do  conversion at SONET interface • APS of WDM must not interfere with that of SONET • must react faster than SONET (50 ms) • recovery at lower level (WDM) 1st • Recall: WDM restoration is faster but detection is slower

43. 9. SONET and WDM • E.G. on WDM ring a WXC can directly drop and add into the optical medium the  used in the SONET ring • Organizations dealing with interoperability issues • Optical Internetworking Forum (www.oiforum.com) • ITU-T Study Group 15 (www.itu.int/ITU-T/com15/index.html) • SONET Interoperability Forum (www.atis.org/atis/sif/sifhom.htm)

44. 10. Control Plane for WDM Switches/Routers • WDM OTN networks need to support • APS • QoS • Monitoring • Security • Interoperability (SONET, PON, ....) • Each device (edge or core) needs to support some or all points above • need to define frame format • signaling protocols (setup and teardown of  paths) • MIB’s • management protocols

45. 10. Control Plane for WDM Switches/Routers • A uniform control plane that is distributed, supporting heterogeneous environments is needed • Recall: SONET suffers immensely from lack of a standardized management platform • Ongoing effort to integrate, control, and manage existing networks in a vendor independent way [24] • CORBA’s Xo/JIDM specification is a foundation [5] • joint effort by major Telco. Industries • integrates management and control architectures for • ATM, SONET, WDM, IP, and others • This allows WDM networks to fully support OAM&P • i.e. operations, administration, maintenance, and provisioning

46. 11. Direction of WDM Networks • More than just the current point-to-point “fat-pipe” capacity • IP over WDM/DWM for OTN support • OSPF/MPLS/RSVP • increase in: control, monitoring, & management • Support for QoS reaching into core • Advances in tuned lasers, filters,  converters • increase in tuning speed and range • increase in  window along base ’s (1300,1500 nm) • allow WDM to become circuit/packet switched networks offering value-added features opening up diverse IP and WDM services to the paying public

47. 12. Conclusion • Currently WDM applied in increasing point-to-point capacity • Increasing towards providing WDM OTN with value added features • WDM / SONET Integration • Many critical components missing: • IP over WDM protocol integration • Control Plane • Traffic monitoring and measurement • Traffic engineering • QoS developed leveraging above protocols • WDM access networks supporting QoS

48. 13. References [1] J. Elmirghani and H. Mouftah, “Technologies and Architectures for Scalable Dynamic Dense WDM Networks,” IEEE Commun. Mag., vol. 38, no. 2, February 2000, pp. 58-66. [2] N. Golmie, T. Ndousse and D. Su, “A Differentiated Optical Services Model for WDM Networks,” IEEE Commun. Mag., vol. 38, no. 2, February 2000, pp. 68-73. [3] I. Van de Voorde, and C. Martin, “The SuperPON Demonstrator: An Exploration of Possible Evolution Paths for Optical Networks,” IEEE Commun. Mag., vol. 38, no. 2, February 2000, pp. 74-82. [4] S. Yao and B. Mukherjee, “Advances in Photonic Packet Switching: An Overview,” IEEE Commun. Mag., vol. 38, no. 2, February 2000, pp. 84-94. [5] D. Cavendish, “Evolution of Optical Transport Technologies: From SONET/SDH to WDM” IEEE Commun. Mag., vol. 38, no. 6, June 2000, pp. 164-172. [6] Y. Ye, S. Dixit and M. Ali, “On Joint Protection/Restoration in IP-Centric DWDM-Based Optical Networks” IEEE Commun. Mag., vol. 38, no. 6, June 2000, pp. 174-183. [7] J. Jang and E. Park, “On Joint Protection/Restoration in IP-Centric DWDM-Based Optical Networks” IEEE Commun. Mag., vol. 38, no. 6, June 2000, pp. 174-183. [8] S. Johansson et al., "A Cost‑Effective Approach to Introduce an Optical WDM Network in the Metropolitan Environment," IEEEJSAC, vol. 16, no. 7, Sept. 1998, pp. 1109‑22. [9] S. Ramamurthy and B. Mukherjee, "Survivable WDM Mesh Networks, Part I ‑ Protection," Proc. INFOCOM'99, Vol. 2, 1999, pp. 744‑51. [10] A. Mokhtar and M. Aziziglu, "Adaptive Wavelength Routing in All‑Optical Networks," IEEE/ACM Trans. Net., vol. 6, no. 2,Apr. 1998, pp. 197‑206.

49. 13. References [11] P. Demeesteretal., "Resilience in Multilayer Networks," IEEE Commun. Mag., Aug. 1999, vol. 37, no. 8, pp. 70‑76. [12] S. Shew, "Fast Restoration of MPLS Label Switched Paths," Internet draft, work in progress, Oct. 1999. [13] S. Makam et al., "Protection/Restoration of MPLS Net­works," Internet draft, work in progress, June 1999. [14] M. Medard, S. Finn, and R. Barry, "WDM Loop‑back Recovery in Mesh Network," Proc. IEEE INFOCOM '99, vol. 2, pp. 752‑59. [15] D. J. Blumenthal et al., "Special Issue on Photonic Pack­et Switching Technologies, Techniques and Systems," 1EEE/OSA J. Lightwave Tech., vol. 16, no. 12, Dec. 1998. [16] H. T. Mouftah and J. M. H. Elmirghani, “Photonic Switching Technology‑Systems and Networks”, IEEE Press, July 1998. [17] R. L. Cruz et al. (Eds.), "Special Issue on Optical Net­works," IEEE JSAC, vol. 14, no. 5, June 1996. [18] M. Fujiwara et al. (Eds.), "Special issue on Multiwave­length Optical Technology and Networks," IEEEIOSA J. Lightwave Tech., vol. 14, no. 6, June 1996. [19] M. Wang, Ed., Feature Topic on Multiwavelength Fiber Optic Communication, IEEE Commun. Mag., vol. 36, no. 12, Dec. 1998. [20] D. A. Smith et al., "Evolution of the Acousto‑Optic Wavelength Routing Switch," 1EEE1OSA J. Lightwave Tech., vol. 14, no. 6, June 1996, pp. 1005‑19.

50. 13. References [21] D. Awduche et al., "Multiprotocol Lambda Switching," Internet draft, work in progress, Nov. 1999. [22] ITU‑T Rec. G.709, "Network Node Interface for the Optical Transport Networks," work in progress, SG 15. [23] ITU‑T Rec. G.957, "Optical Interfaces for Equipments and Systems Relating to the Synchronous Digital Hierarchy," July 1995. [24] R. Pease, "Companies Demonstrate Multivendor, Multi­technology Network Management," Lightwave, Nov. 1999. [25] J. Manchester, P. Bonenfant, and C. Newton, "The Evolution of Transport Network Survivability," IEEE Commun. Mag., vol. 37, no. 8, Aug. 1999, pp. 44‑57.