Optical Networks, Current and Future Technologies for WDM By: Bogdan Ionescu DSRG, University of...

Optical Networks,Current and Future Technologies for WDM

By: Bogdan Ionescu

DSRG, University of OttawaJuly 5, 2000

1. Purpose2. Introduction to WDM3. Current Technology Standpoint4. WDM Network Topologies and Architectures5. Failure Resiliency6. Switching and Routing 7. QoS in WDM8. Access Networks9. SONET and WDM10. Control Plane for WDM Networks11. Direction of WDM Networks12. Conclusion

1. Purpose

• Board study of WDM technology• Deployment• Work in progress• Establish future research areas in WDM

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

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

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

Component PurposeTuned Lasers Signal GenerationMulti-frequency Lasers Signal Generation, Mux/Dmux, RoutingTunable Filters Circuit and Packet Switching, used in WR

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

10 – 20 nm 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

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 1 – 10 ms 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

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

2. Introduction(WDM Network Components)

• Reconfigurable routing switches

a) employing converters b) employing photonic switches

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.

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


• Broadcast and Select Topologies [1]


• 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)


• 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]


• Routing Networks


• 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]


• 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


• 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


• Example of interconnected WDM network infrastructure; Mesh, Ring, and Access ( Discussed Later )

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

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)


• 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


• 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

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


• Detection and restoration at different layers


• 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 MPS [21]

• sharing of information between IP & WDM layers• IP to directly access WDM channels


• 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


• 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

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


• 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


• 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


• 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


• 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

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

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

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 Unsecured

Provisioning 3R 2R 1R

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

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]

8. Access Networks

• Example of current Access Networks for WDM

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

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

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)

http://www.oiforum.com/

http://www.itu.int/ITU-T/com15/index.html

http://www.atis.org/atis/sif/sifhom.htm

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

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

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

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

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.

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 Net works," 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 Pack et 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 Net works," IEEE JSAC, vol. 14, no. 5, June 1996. [18] M. Fujiwara et al. (Eds.), "Special issue on Multiwave length 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.

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, Multi technology 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.

Date post:	30-Mar-2015
Category:	Documents
Upload:	lesly-rankin
View:	217 times
Download:	0 times

Optical Networks, Current and Future Technologies for WDM By: Bogdan Ionescu DSRG, University of...

Documents