73rd IETF – Minneapolis, MN, November 2008Page - 1

A Framework for the Control and Measurement of Wavelength Switched Optical Networks

(WSON) with Impairments

Greg Bernstein gregb@grotto-networking.comGrotto Networking

Young Lee ylee@huawei.com

Huawei

Dan Li danli@huawei.com

Huawei

draft-bernstein-ccamp-wson-impairments-01.txt

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Contributors

• Ming Chen (Huawei)

• Rebecca Han (Huawei)

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A Framework for WSONs with Impairments

• What are impairments and how do they relate to routing:– Physical processes that can alter an optical

signal during transmission or other processing such as switching

– RFC4054 gives an overview

• Who defines optical impairments?– ITU-T has an extensive recommendations that

include terminology, definitions and measurement techniques.

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ITU-T References1. [G.650.1] ITU-T Recommendation G.650.1, Definitions and test methods for linear, deterministic attributes of single-mode

fibre and cable, June 2004.2. [650.2] ITU-T Recommendation G.650.2, Definitions and test methods for statistical and non-linear related attributes of

single-mode fibre and cable, July 2007.3. [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode optical fibre and cable, June 2005. 4. [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion-shifted single-mode optical fibre and cable, December

2006.5. [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off shifted single-mode optical fibre and cable, December

2006.6. [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable,

March 2006.7. [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and cable with non-zero dispersion for wideband optical

transport, December 2006.8. [G.661] ITU-T Recommendation G.661, Definition and test methods for the relevant generic parameters of optical

amplifier devices and subsystems, March 2006.9. [G.662] ITU-T Recommendation G.662, Generic characteristics of optical amplifier devices and subsystems, July 2005.10. [G.671] ITU-T Recommendation G.671, Transmission characteristics of optical components and subsystems, January

2005.11. [G.680] ITU-T Recommendation G.680, Physical transfer functions of optical network elements, July 2007.12. [G.691] ITU-T Recommendation G.691, Optical interfaces for multichannel systems with optical amplifiers, November

1998.13. [G.692] ITU-T Recommendation G.692, Optical interfaces for single channel STM-64 and other SDH systems with

optical amplifiers, March 2006.14. [G.872] ITU-T Recommendation G.872, Architecture of optical transport networks, November 2001.15. [G.957] ITU-T Recommendation G.957, Optical interfaces for equipments and systems relating to the synchronous

digital hierarchy, March 2006.16. [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network Physical Layer Interfaces, March 2006.17. [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, June 2002.18. [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM applications: CWDM wavelength grid, December 2003.19. [G.Sup39] ITU-T Series G Supplement 39, Optical system design and engineering considerations, February 2006.

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Control Plane related Applications

• Impairment Aware Path Computation and Control– Our focus here– Includes path establishment and teardown

• Measurement of Optical Connection Quality– Interesting potential application of control

plane but we don’t address this here.

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Impairment Framework Goals

• Relate the application area to the GMPLS and PCE control plane (also see Giovanni)

• Decompose and classify various reasonable approaches -- Very important to get folks on the same page--

• Identify, define and classify: terminology, nomenclature, parameters -- Here we reference ITU-T, but more classification for control plane purposes is useful (see Imp-Info and Giovanni)

• Look for commonality and difference among approaches with respect to: (a) shared information, (b) procedures, (c) actors (entities involved)

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Approaches to Impairments in WSONs

1. Networks designed such that every possible path is conformant for all the signal types permitted on the network (“impairment free case”)

2. Networks in which a limited number of pre-calculated paths are conformant for each type of signal permitted in the network. (no knowledge of impairments in the control plane)

3. Networks in which impairment effects can be estimated via approximation techniques (impairment info needed)

4. Networks in which impairment effects must be more accurately estimated. Typically via “simulation” (impairment info needed)

ITU-T Question 12/15 Working Group List

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Impairment Aware RWA Computation

• Three conceptual functions– Routing (WSON Framework)

• Finding one or more paths from source to destination

– Wavelength Assignment (WSON Framework)• Selecting a wavelength/wavelengths to use along a

path

– Impairment Validation (IV) -- new• Determining if the impairments encountered by a

specific signal on this selected path and wavelength result in unacceptable degradation in received signal quality.

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Architectural Alternatives

• Combined Routing, WA, and IV– Routing (R), Wavelength Assignment (WA) and

Impairment Validation (IV) performed on a single entity, e.g., PCE. This doesn’t specify algorithms or procedures. Does need some type of impairment information (cases 3 & 4)

• Routing + WA + IV– Splitting all or any of these functions amongst different

entities.

• Routing + Distributed WA/IV– Performing either WA or IV or both in a distributed

fashion via a signaling protocol.

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R+WA+IV

• R+WA+IV – separate routing, wavelength assignment, and impairment

validation

• R + (WA & IV) – routing separate from a combined wavelength assignment and

impairment validation process. Note that impairment validation is typically wavelength dependent hence combining WA with IV can lead to efficiencies.

• (RWA)+IV – combined routing and wavelength assignment with a separate

impairment validation process.

Control plane implications: getting required information to computational entities and communications between entities, does not require additional signaling modifications

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Routing and Distributed WA/IV

• RWA + Distributed IV – Does IV for only a particular wavelength

• R + Distributed WA & IV– Needs to perform IV for each potential

wavelength and carry this information as long as the potential wavelength is under consideration.

Control plane implications: modification of signaling protocols, does not require impairment information distribution.

Valid for Case 3: Approximate Impairment computation

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Next Steps/Issues

• Assess interest in an Impairment Framework

• Relation to other drafts?

• Continue discussions with ITU-T