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The hardware aspects of SONET are difficult to describe in discrete terms, as many of the functional elements overlap. Just as manufacturers of traditional voice and data equipment often build multiple functional elements under the skin of a single box, so do SONET/SDH equipment manufacturers. Given that caveat, the following is a description of discrete functional aspects of hardware devices.
Figure 10.6 Terminal Multiplexer (TM) and Add/Drop Multiplexer (ADM) in SONET application.
SONET offers a number of advantages in addition to the inherent advantages of fiber optic transmission systems. Certainly, the fact that SONET is highly standardized offers the benefits of interconnectivity and interoperability between equipment of different manufacturers. That translates into freedom of vendor choice and yields lower costs through competition. Additionally, SONET/SDH is extendible to the premise on a fully interoperable basis. While such extension currently is unusual for SONET, such deployment provides end-to-end advantages of enhanced bandwidth, error performance, dynamic bandwidth allocation, and network management. In an end-to-end deployment scenario, SONET is particularly attractive in support of broadband services such as SMDS, Frame Relay, ATM and, ultimately, B-ISDN.
In bandwidth-intensive applications, the high absolute cost of SONET can be offset by virtue of its extraordinarily high capacity. Whether deployed in a carrier network or extended to the user premise, SONET supports the aggregation of all forms of traffic, including voice, data, video, image, and facsimile. As a result, a SONET infrastructure can obviate the need for multiple transmission facilities in support of individual services. The simplicity of multiplexing and de-multiplexing via ADMs reduces costs, delay, and error. Clearly, SONET/SDH offers the considerable advantage of network resiliency through its inherent redundancy and self-healing capabilities.
Finally, SONET offers tremendous security, as is the case with fiber optic transmission systems. Fiber is difficult, if not impossible, to physically tap without detection. It is difficult to identify the one channel for detection out of the thousands of information channels supported in a SONET mode. As Francis Bacon said in 1625, There is no secrecy comparable to celerity (of Delay, Essays)speed is a hallmark of SONET.
SONET primarily is deployed in backbone carrier networks where its many advantages can be put to full use. Particularly in a convergence scenario, the carriers have the potential to realize considerable cost savings by using a single fiber infrastructure in support of bandwidth-intensive video and image streams, in addition to voice, data, and facsimile traffic. That scenario ultimately will deliver SONET fiber to the premiseperhaps even to residences.
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