eed temperature control. Thermo-optics are ideally suited to integration. AWG can be integrated with arrays of thermo-optic switches to create an ADM. Polymers are probably the best materials because AWGs Chapter 2 are temperature sensitive and polymers keep the heat localized at the switch. As a waveguide approach, thermo-optics eliminates beam alignment issues created by free-space approaches, but are susceptible to crosstalk, polarization dependence, and loss issues. Acousto-optics uses sound waves to deflect light that passes through crystals or fused couplers. Acousto-optics will be used for wavelength- selective switches. With holograms, electrically energized Bragg gratings are created inside a crystal. When voltage is applied, the grating deflects the light to an out- put port. With no voltage, the light passes straight through. Holograms compete with 3D MEMS on scalability, but are better suited to switching individual wavelengths rather than groups of wavelengths. Their nanosec- ond switching speed means that holograms can be used for optical packet- by-packet routing. Like LXT, holograms can support drop-and-continue applications. 2.10 Standardization Activities Let's briefly take stock of standardization activities by the ITU, Internet Engineering Task Force (IETF), Optical Domain Service Interconnect (ODSI), and Optical Internetworking Forum (OIF), particularly with regards to the ION. They focus on the Optical UNI (O-UNI) and the Optical NNI (O-NNI). Proponents envision intranet routers issuing commands across an O- UNI to set up lightpaths over carrier-provided networks. Some hopefully baselined their vision of architectures for commercial, service-supporting networks on the collapsed network illustrated in Figure 2-55. As enticing as the prospect is, this network vision isn't realistic and will probably never be attained in the United States, unless we decide to reestablish the Bell Sys- tem or a comparable surrogate. Nonetheless, you will find commercial requirements for control that were designe