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This is clearly problematic if client gears lack carrier-grade support. For example, service protection may have to use slower Ethernet rapid spanning tree protocol (RSTP) or MPLS rerouting protocols. Although Ethernet interface ports could possibly incorporate 1+1 fiber protection, few vendors support this option. Similarly, carrier-grade OAM support may be limited as associated Ethernet OAM standards will take time to mature. In general, EoF will give much lower fiber resource utilization and higher overbuild, since few leasing clients will deploy CWDM/DWDM systems to exploit unused wavelength capacities. This solution is, therefore, only feasible in smaller, fiber-rich scenarios with relaxed fault-tolerance and OAM needs. A much more scalable and efficient EPL approach is to map native optical Ethernet interfaces onto WDM lightpaths Ethernet over WDM (EoWDM) as shown in Figure 8.6. The economics of this collapsed transparent solution are very compelling, especially for carriers with existing DWDM infrastructures. For example, an Ethernet packet can leave a server via a Gigabit Ethernet DWDM interface, move across a metro ROADM ring, and be received on a workstation all without costly intermediate SONET/SDH or ATM/Frame Relay electronics. From the data-plane perspective, EoWDM (like EoF) can also provide highly stringent circuit-like QoS guarantees. Nevertheless, its geographic coverage is much greater than EoF, as amplified DWDM networks can readily span over 1000 km. Moreover, EoWDM is vastly more bandwidth scalable than EoF by almost two orders of magnitude and new third-generation DWDM ROADM nodes can provide much faster service velocity (minutes and hours). EoWDM can also leverage the full range of WDM survivability schemes (see Figure 8.5) to offer multiple tiered (i.e., differentiated and value-added) EPL packages. Some examples are shown in Table 8.5 and include high-end EPL services using dedicated protection (1+1 span, UPSR, and mesh protection) to more wavelength-efficient services using shared protection (SPRING, shared mesh protection, and mesh restoration). Also note that EoWDM

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In previous chapters, several methods of interconnecting the motors with the wheels have been discussed. In direct-drive methods, the motor or gearmotor s output shaft is connected directly to the wheels (see Figure 6-5). Indirect-drive methods include a chain, belt, and even a series of flexible couplings. The following sections will discuss various chain and belt drive systems. Numerous types of flexible shaft couplings are available, such as universal joints, shear couplings, spider couplings, grid couplings, offset couplings, chain couplings, gear and sleeve couplings, bellows couplings, and helical beam couplings. The main advantage of these shaft couplings is that they can connect two shafts that are slightly misaligned. Figure 6-6 shows a Lovejoy flexible coupling. A Lovejoy coupling is a spider coupling. They come with three different parts: two bodies and a spider. The shaft bodies come with different bore diameters so that different shaft diameters can be coupled together. The spider s material is made out of urethane, Hytrel, or rubber. The selection of the spider material is based on the applications the coupling is going to be used for. For high-powered robots, careful design of the components and mounting locations will be needed to minimize shaft misalignment.

Summary

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The use of objects in 3D models renders them more usable and efficient in the BIM process. An object generally represents a physical entity (although nonphysical entities, e.g., events such as inspections, can also be represented by objects) in the project and is able to contain information relevant to the project. Objects are often composed of many parts that would be much more burdensome to the project model if treated as separate parts. See also Library Part.

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