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Method for Fault Detection in Optical Networks Disclosure Number: IPCOM000196976D
Publication Date: 2010-Jun-22
Document File: 3 page(s) / 1M

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Method for Fault Detection in Optical Networks

Nokia Siemens Networks
Dominic Schupke, Beate Konrad
Most of today's metro networks are low cost solutions rather than costly full-blown long-haul networks. Net- work management functionality is basic and done via transponder-based General Communication Channel (GCC) and not via an Optical Supervisory Channel (OSC) on an extra wavelength affording extra hard- ware. Therefore, these networks often do not provide detection schemes like OMS (Optical Multiplex Sec- tion) and cannot explicitly localize failed OMS, e.g. broken fibers.

The situation causes high failure localization efforts by on-site inspection (OPEX: OPerational EXpenditure) which is time-consuming. A solution would be to use OSCs which requires additional hardware and leads to higher CAPEX (CAPital Expenditure). Another option is to accomplish a Root Cause Analysis (RCA) based on the failure pattern that is seen by receivers at tran- sponders/regenerators. The latter is typically insuffi- cient to localize the failed OMS since many different failed OMSs produce the same patterns. The most re- liable option is to combine the mentioned protection

efforts but that affords doubling of transponders/re- generators and adds a high amount of CAPEX.

As a new idea, a method is proposed to establish fail- ure analysis and restoration in optical networks, espe- cially DWDM (Dense Wavelength Division Multiplex) metro networks, with wavelength selective switches, e.g. ROADMs (Reconfigurable Optical Add-Drop Multiplexer).

The main idea is to use the broadcast and select fea- ture of ROADMs to let surviving channels probe into neighboring paths to localize the failed OMS. The un- used copy of the surviving channel is not blocked but transmitted to a transponder at a different site via a possibly failed OMS, thereby.

Core piece of the proposed solution is the broadcast and select feature and the so called "drop and con- tinue" feature, respectively, provided by most of the ROADM architectures. Cost-effective ROADMs which are preferred for metro and access networks are built

Figure 1: The failure case


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of a splitter at the DEMUX (DEMUltipleXer) side and a WSS (Wavelength-Selective Switches) at the MUX (MUltipleXer) side. Normally, a channel is either dropped at the DEMUX side or transparently passed to the MUX side whereas the unused path within the ROADM is blocked by high attenuation or left open. Within the proposed idea, an express path not used for data traffic will not be blocked but the respective wave- length will be routed further as a probe signal in order to localize a failed OMS.

The approach assumes that

• the network management is aware of all working optical paths and all demands that are present in the network.

• the network is sufficiently meshed...