Optical Layer Protection Schemes

1. 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

2. 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)

3. 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

4. 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

5. 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

6. 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

7. 1+1 OCh Dedicated Protection

8. 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

9. Unidirectional Path-Switched Rings (UPSR)