ame "mission-critical," its deployment became more innovative, and soon it was deployed in ring architectures as shown in Figure 3-51. These rings represent one of the most commonly deployed network topologies. For the moment, however, let's examine a point-to-point deployment. As it turns out, rings don't differ all that much. Figure 3-51 Ring archi- tectures used in SONET Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Chapter 3 If we consider the structure and function of the typical point-to-point circuit, we find a variety of devices and "functional regions" as shown in Figure 3-52. The components include end devices, multiplexers in this case, which provide the point of entry for traffic originating in the cus- tomer's equipment and seeking transport across the network; a full- duplex circuit, which provides simultaneous two-way transmission between the network components; a series of repeaters or regenerators, responsible for periodically reframing and regenerating the digital sig- nal; and one or more intermediate multiplexers, which serve as nothing more than pass-through devices. When non-SONET traffic is transmitted into a SONET network, it is packaged for transport through a step-by-step, quasi-hierarchical process that attempts to make reasonably good use of the available network bandwidth and ensure that receiving devices can interpret the data when it arrives. The intermediate devices-including multiplexers and repeaters-also play a role in guaranteeing traffic integrity. To that end, the SONET standards divide the network into three "regions": path, line, and section. To understand the differences between the three, let's follow a typical transmission of a DS3, probably carrying 28 T1s, from its origi- nation point to the destination. When the DS3 first enters the network, the ingress SONET multi- plexer packages it