 untenable, they withheld any and all funding, even to those carriers that always stated more achievable numbers in the 40 percent gross/20 percent net range and who had compelling business cases. While waiting for the deployment of full ION, we are likely to see less encompassing architectures evolve, such as semiautomated OTNs. The semiautomation applies to provisioning as well as to restoration. For exam- ple, optical protection is an important requirement in metro optical net- works (MONs), especially for those services that are natively unprotected, such as Fibre Channel and so on. Currently, two-fiber optical uni-/bidirec- tional path-switched ring (2F-OUPSR/2F-OBPSR) methodologies are typi- cal. The issue is that these protection schemes require a high amount of redundancy. This is because these schemes offer dedicated protection. In order to achieve more efficient protection, techniques that support optical shared protection have to be deployed. A number of concepts exist, includ- ing two-fiber shared-lambda protection rings (2F-SXPR) and four-fiber opti- cal bidirectional line-switched rings (4F-OBLSR).11 Both of these techniques require switch matrices and/or OADMs as basic elements; small switches or OADMs support the capability of shared protection. SXPR methods can lead to substantial equipment/fiber savings given that the ring traffic pattern is the nonhubbed type. Figure 7-10 shows the traffic pattern of a fully meshed four-node ring with eight bidirectional channels between each pair of nodes. 12 Table 7-2 compares SAPR and the commonly used OUPSR/OBPSR approach. A total of 32 wavelengths and the traffic pattern from Figure 7-10 are assumed in the table. Optical channel shared protec- tion is viewed by proponents as one of the best solutions for realizing OTN survivability. Standby wavelengths are shared and signals are switched by a wavelength switch. Chapter 7 Figure 7-10 SXPRs. Site A Site B Site C Site D Table 7-2 Ring Systems with 32 Wavelengths Comparison Between SAPR and No. of transponders