Wavelength Switched Optical Networks

Wavelength Switched Optical Networks (WSON) are Wavelength Division Multiplexing (WDM) based networks that include switching elements that can switch based on the wavelength or the frequency of signals transported over optical fiber. Although originally included in the overall set of Generalized Multi-Protocol Label Switching (GMPLS) based control plane protocols, optical technology developments have gone beyond the optical systems originally envisioned within GMPLS. Hence this work extended GMPLS and related technologies, in particular, the path computation element (PCE) to provide robust control of these more modern optical networks.

The basic WSON control plane standards thrust was divided into the following areas:

• Overall control plane approach to WSONs including key scope limitations of this initial effort.
• An information model and encoding for use in path computation for WSONs. In the optical literature this path computation process is denoted by routing and wavelength assignment (RWA)
• Extensions to the PCE communications protocol (PCEP) to allow path computation clients to request from a PCE server paths meeting WSON constraints and optimization criteria.
• Extensions to GMPLS routing protocols (OSPF, IS-IS) to convey additional information relevant to WSONs.
• Extensions to the GMPLS signaling protocol (RSVP-TE) to facilitate the setup and tear down of WSON connections.
• Considerations of optical impairments and the control plane (in close collaboration with ITU-T)

Status: All the documents here are now IETF RFCs. Thanks to all who contributed to this work!

Framework for GMPLS and PCE Control of WSONs (RFC6163)

Abstract

This document provides a framework for applying Generalized Multi-Protocol Label Switching (GMPLS) and the Path Computation Element (PCE) architecture to the control of Wavelength Switched Optical Networks (WSONs). In particular, it examines Routing and Wavelength Assignment (RWA) of optical paths.

This document focuses on topological elements and path selection constraints that are common across different WSON environments; as such, it does not address optical impairments in any depth.

Status

This document became an IETF RFC in April 2011.

Routing and Wavelength Assignment Information Model for WSONs (RFC7446)

Abstract

This document provides a model of information needed by the routing and wavelength assignment (RWA) process in wavelength switched optical networks (WSONs). The purpose of the information described in this model is to facilitate constrained lightpath computation in WSONs. This model takes into account compatibility constraints between WSON signal attributes and network elements but does not include constraints due to optical impairments. Aspects of this information that may be of use to other technologies utilizing a GMPLS control plane are discussed.

Status and Background

This document became IETF RFC on February 2015.

For extended discussion and examples of WDM switch modeling be sure to read the paper "Modeling WDM Wavelength Switching Systems for use in Automated Path Computation". Note that drawing detailed diagrams of various WDM switching devices is nearly impossible with ASCII line art as required in Internet Drafts and RFCs so we've relegated detailed examples and figures to this paper.

We have introduced a representation for wavelength converter pools that may exist in WSON switches. This is a minimal state approximate model. Similar in spirit to the general WSON switch model that is already in the IETF document. We have written a preliminary draft of a tutorial paper on this representation model.

Routing and Wavelength Assignment Information Encoding for WSONs (RFC7581)

Abstract

A wavelength switched optical network (WSON) requires that certain key information elements are made available to facilitate path computation and the establishment of label switching paths (LSPs). The information model described in "Routing and Wavelength Assignment Information for Wavelength Switched Optical Networks" shows what information is required at specific points in the WSON. Part of the WSON information model contains aspects that may be of general applicability to other technologies, while other parts are fairly specific to WSONs.

This document provides efficient, protocol-agnostic encodings for the WSON specific information elements. It is intended that protocol-specific documents will reference this memo to describe how information is carried for specific uses. Such encodings can be used to extend GMPLS signaling and routing protocols. In addition these encodings could be used by other mechanisms to convey this same information to a path computation element (PCE).

Status and Background

This document became an IETF RFC in June 2015.

General Network Element Constraint Encoding for GMPLS-Controlled Networks (RFC7579)

Abstract

Generalized Multiprotocol Label Switching (GMPLS) can be used to control a wide variety of technologies. In some of these technologies, network elements and links may impose additional routing constraints such as asymmetric switch connectivity, non-local label assignment, and label range limitations on links.

This document provides efficient, protocol-agnostic encodings for general information elements representing connectivity and label constraints as well as label availability. It is intended that protocol-specific documents will reference this memo to describe how information is carried for specific uses.

Status and Background

This document became an IETF RFC in June 2015.

PCEP Requirements for WSON Routing and Wavelength Assignment (RFC7449)

Abstract

This memo provides application-specific requirements for the Path Computation Element Communication Protocol (PCEP) for the support of Wavelength Switched Optical Networks (WSONs). Lightpath provisioning in WSONs requires a Routing and Wavelength Assignment (RWA) process. From a path computation perspective, wavelength assignment is the process of determining which wavelength can be used on each hop of a path and forms an additional routing constraint to optical light path computation. Requirements for PCEP extensions in support of optical impairments will be addressed in a separate document.

Status and Background

This document became an IETF RFC in February 2015.

Signaling Extensions for WSONs (RFC7689)

Abstract

This memo provides extensions to Generalized Multi-Protocol Label Switching (GMPLS) signaling for control of wavelength switched optical networks (WSON). Such extensions are necessary in WSONs under a number of conditions including: (a) when optional processing, such as regeneration, must be indicated to occur at specific nodes along a path, (b) where equipment must be configured to accept an optical signal with specific attributes, or (c) where equipment must be configured to output an optical signal with specific attributes. In addition this memo provides mechanisms to support distributed wavelength assignment in bidirectional LSP, and choice in distributed wavelength assignment algorithms. These extensions build on previous work for the control of lambda and G.709 based networks.

Background and Status

This document became an IETF RFC in November 2015.

OSPF-TE Extensions for General Network Element Constraints (RFC7580)

Abstract

Generalized Multiprotocol Label Switching (GMPLS) can be used to control a wide variety of technologies including packet switching (e.g., MPLS), time division (e.g., Synchronous Optical Network / Synchronous Digital Hierarchy (SONET/SDH) and Optical Transport Network (OTN)), wavelength (lambdas), and spatial switching (e.g., incoming port or fiber to outgoing port or fiber). In some of these technologies, network elements and links may impose additional routing constraints such as asymmetric switch connectivity, non- local label assignment, and label range limitations on links. This document describes Open Shortest Path First (OSPF) routing protocol extensions to support these kinds of constraints under the control of GMPLS.

Background and Status

This document became an IETF RFC in June 2015.

OSPF Enhancement for Signal and Network Element Compatibility for WSONs (RFC7688)

Abstract

This document provides GMPLS OSPF routing enhancements to support signal compatibility constraints associated with WSON network elements. These routing enhancements are required in common optical or hybrid electro-optical networks where not all of the optical signals in the network are compatible with all network elements participating in the network.

This compatibility constraint model is applicable to common optical or hybrid electro optical systems such as OEO switches, regenerators, and wavelength converters since such systems can be limited to processing only certain types of WSON signals.
 

Background and Status

This document became an IETF RFC in November 2015.

A Framework for the Control and Measurement of WSONs with Impairments (RFC6566)

Abstract

As an optical signal progresses along its path, it may be altered by the various physical processes in the optical fibers and devices it encounters. When such alterations result in signal degradation, these processes are usually referred to as "impairments". These physical characteristics may be important constraints to consider when using a GMPLS control plane to support path setup and maintenance in wavelength switched optical networks. This document provides a framework for applying GMPLS protocols and the Path Computation Element (PCE) architecture to support Impairment-Aware Routing and Wavelength Assignment (IA-RWA) in wavelength switched optical networks. Specifically, this document discusses key computing constraints, scenarios, and architectural processes: routing, wavelength assignment, and impairment validation. This document does not define optical data plane aspects; impairment parameters; or measurement of, or assessment and qualification of, a route; rather, it describes the architectural and information components for protocol solutions.