Optical Layer Protection Schemes Layers within the optical layer Optical channel (OCh) layer (path layer): end-to-end routing of the lightpaths Optical multiplex section (OMS) layer (line layer): links between OLTs and OADMs OCh layer protection schemes restore one lightpath at a time Need demultiplex all wavelengths OMS layer protection schemes restore the entire group of lightpaths on a link Require less equipment

Optical Layer Protection Schemes OLTs and OADMs can provide both OCh and OMS layer protection in linear or ring configurations OXCs can provide OCh layer protection in linear, ring, and mesh configurations Two choices for protection Use unprotected WDM point-to-point systems and rely on OXCs to perform the protection functions (backbone networks) Rely on the WDM line terminals and OADMs to perform the protection functions (metropolitan networks)

1+1 OMS Protection At one end, the composite WDM signal is bridged onto two diverse paths using an optical splitter At the other end, an optical switch selects the better among the two signals

1:1 OMS Protection Use a switch at the transmitter, instead of a splitter The composite WDM signal is transmitted over only the working fiber If the working fiber is cut, the source and both ends switch over to the protection fiber An APS protocol is needed Benefits Support low priority traffic on the protection fiber Allow N working systems to share a single protection scheme

OMS-DPRing Dedicated protection ring 2 fibers, operate at the OMS layer Each node transmits on both directions of the ring Different nodes must transmit at different wavelengths Normal operation: the ring functions as a bus, with one pair of amplifiers turned off and all the others turned on When a link fails: the amplifiers next to the failed link are turned off and the ones that were originally inactive are turned on

OMS-SPRing Shared protection ring with 4 fibers, analogous to a SONET BLSR/4 The two protection fibers do not have attached WDM equipment Use either span switch or ring switch Two-fiber version of OMS-SPRing Dedicate half the wavelengths on each fiber for protection purposes Make the protection wavelengths on one fiber correspond to the working wavelengths on the other fibersignals can be rerouted w/o requiring wavelength conversion

1+1 OCh Dedicated Protection

Protection in SONET: Self-Healing Rings A ring is the simplest topology that is 2-connectedresilient to failures Much of the carrier infrastructure today uses SONET rings called self-healing rings Can automatically detect failures and reroute traffic away from the failed links/nodes rapidly (within 60ms) Three widely deployed ring architectures: UPSR, BLSR/4, BLSR/2 Unidirectional ring: carry working traffic in only one direction of the ring Bidirectional ring: carry working traffic in both directions

Unidirectional Path-Switched Rings (UPSR)