the signal is again converted back into a light pulse. This process accounts for about half the cost of optical networking. Advances in optical amplifiers, solitons (laser pulses that retain their shape in a fiber over long dis- tances), and optical add/drop multiplexers (OADMs) and cross-connects (which eliminate the need for any conversions for signals passing through the nodes) are vastly improving the performance of optical infrastructures while also reducing the costs of deployment and ongoing operation. Third, the provisioning of services needs to occur in minutes. But at this point, a carrier may have to wait six to nine months for an OC-3 (i.e., 155Mbps) circuit to be provisioned. Optical switches will automate the provisioning process while also boosting capacities to handle thousands of wavelengths; that is the promise of end- to-end optical networking. Optical Networking Today and Tomorrow As described in Chapter 2, "Traditional Transmission Media," today's networks maintain mostly separate electronic connections for voice and data (see Figure 11.1). They achieve reliability in the network by using dual-counter-rotating rings based on the SDH/SONET communications standard (which is discussed in Chapter 4, "The PSTN"). With dual-counter-rotating rings, traffic normally flows in a clock- wise direction over the primary fiber. A protect fiber is designed to carry traffic in a counterclockwise direction. An SDH/SONET multiplexer aggregates traffic onto the rings. If the primary link is cut, traffic is switched to the protect fiber very quickly-in about 50 milliseconds. This ensures a high degree of network surviv- ability, and it is a major strength of SDH/SONET. The first generations of WDM equipment did not address network restoration, but newer equipment now pos- sesses such features as well. Optical networks in the near future will channel all traffic over a single fiber connection and will provide redundancy by using the Internet's mesh of interlock- ing pathways. When a line breaks, traffic can flow 