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Current and Future Technologies for WDM DSRG, University of Ottawa

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1 Current and Future Technologies for WDM DSRG, University of Ottawa
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 ( 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] Source Category
Tuning Range Tuning Time Comments Mechanically tuned lasers 10 – 20 nm 100 – 500 ms Mechanically tuning of the facets FP external cavity Acousto-optically and electro-optically tuned lasers Tens of s Good for packet switching Injection current tuned lasers 4 nm 0.5 – 10 ns e.g. limited tuning range Switched Sources Switched < 65 ps Integration improves functionality and speed Array sources (using AWG) Typically 16 channels spaced by 200 GHz 100 – 200 ms Locked  and temperature tuning of whole comb by 275 GHz Array sources (DFB) Limited by number of elements in array 1 – 10 ns DFB lasers act independently, and can drift to cause crosstalk

8 2. Introduction Characteristics of tunable filters [1] Filter Category
Tuning Range Tuning Time Comments Fabry-Perot 500 nm 1 – 10 ms Fiber implementation available Acousto-optic 250 nm 10 s Can be used as a router as well AWG tunable filter 40 nm 10 ms Thermo-optic tuning Liquid crystal Fabry-Perot 30 nm 0.5 – 10 s Lower power consumption (< 1mW) Electro-optic 16 nm 1 – 10 ns Resolvable channels about 10 Fiber Bragg grating 10 nm Temperature or mechanical stretched tuning Cascaded Mach-Zehnder interferometer filters 4 nm 50 ns Mostly used for  conversion Tunable filters based on semiconductor or laser structure 5 nm 0.1 – 1 ns Limited number of channels

9 (WDM Network Components)
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 (WDM Network Components)
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 & 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 & 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 & 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 traffic at “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 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-based traffic 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 distributed algorithm path management establish, maintain, tear-down of 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 Criteria Class 1
(1, 2) Class 2 (3, 4) Class 3 (5, 6) BER 10-9 10-7 10-5 Survivability 90 % 70 % 20 % Monitoring Fine Grained Coarse Grained N/A Security Secure Unsecured Provisioning 3R 2R 1R

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 ( ITU-T Study Group 15 ( SONET Interoperability Forum (

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 [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 [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 [4] S. Yao and B. Mukherjee, “Advances in Photonic Packet Switching: An Overview,” IEEE Commun. Mag., vol. 38, no. 2, February 2000, pp [5] D. Cavendish, “Evolution of Optical Transport Technologies: From SONET/SDH to WDM” IEEE Commun. Mag., vol. 38, no. 6, June 2000, pp [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 [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 [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 [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 [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 [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 [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 [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.

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