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Method of Measuring the L2 Protection Switching Time for Packet Circuits from Transport Telecom Equipment Disclosure Number: IPCOM000020528D
Original Publication Date: 2003-Dec-25
Included in the Prior Art Database: 2003-Dec-25

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Optical Transport Networks based on TDM (Time Division Multiplexing) technologies like SDH/Sonet (Synchronous Digital Hierarchy), WDM (Wavelength Division Multiplexing) or OTN (Optical Transport Network) are technologies that strongly rely on "self-healing" mechanisms in order to guarantee high uptimes. A very important characteristic is the intrinsic time interval in which a protected circuit can automatically recover from impairments, i.e. a physical or logical failure. This is typically measured to characterize the performance of the equipment in connection with available protection schemes like SNCP (Sub-Network Connection Protection), Linear MSP (Multiplex Section Protection) and BSHR (Bidirectional Self Healing Ring), i.e. the switch-over time from "working line" to "protection line". Typically, standards for Automatic Protection Switching (APS) times only allow for intervals as low as 50ms. With evolution of these networks to the NGN (Next Generation Networks) concept, several types of services are to be integrated in the new SDH telecom networks, as for example packet circuit services like Ethernet, or more sophisticated technologies like RPR (Resilient Packet Rings). This led to hybrid equipment, where TDM and packet circuits are simultaneously present on the same network. In some of these the concept of automatic traffic protection mechanisms are also present at the physical layer, whereas the characterization of switching times is yet to be defined. For TDM networks, the Service Disruption Time (SDT) is mostly measured by means of several available switching trigger criteria based on the presence of specific alarms. However, this treaties addresses the packet circuits for which no satisfactory implementation exists.