Network and Service Discovery in Distributed Environments

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) gt 1 Tb/s
• this is DWDM
• e.g. of such optical components 1
• Distributed Feedback Lasers (DFB)
• Erbium-doped Fiber Amplifiers (EDFAs)
• 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 80s and early 90s, one
  of first, built by Bell Core
• 18 ? separated by 2nm modulated _at_ 1.5 Gb/s
  over 57 km
• RAINBOW I II 1 in the early 90s 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 gt 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 VPNs
• 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 _at_ 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 _at_ 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 gt 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.
  WXCs
• 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
• 11 protection
• same signal is transmitted through two
  non-intersecting paths
• destination decides on which signal to choose
• 11 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

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• 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. _at_ 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

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• 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

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• 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

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• 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

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• 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

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• 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 gt jitter
• 1R no retiming and reshaping, simplest and most
  transparent to optical format

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• 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

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• 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
• OADMs (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

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• 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/inde
  x.html)
• SONET Interoperability Forum (www.atis.org/atis/si
  f/sifhom.htm)

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• 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)
• MIBs
• management protocols

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• 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
• CORBAs 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 OAMP
• 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

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