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These two cases have a common thread, showing a shift from a distributed to a centralized management structure triggered by a reduction in market uncertainty. This evidence is powerful, given the many differences between email and voice services, and differences in the infrastructure of the underlying networks on which these services are built. The migration of voice features occurred within the intelligent PSTN (Centrex vs. PBX). Email services built on the distributed end-2-end architecture of the Internet have seen a similar migration of users from distributed ISP-based email to centralized web-based services. The likely cause of users migrating in both these cases is a decrease in market uncertainty, which shows that the theory generalizes to many services, on networks with different infrastructure. The case studies illustrate the theory that a decrease in market uncertainty caused a shift to a more centralized management structure that utilized the resources better, had technical advantages, and because of low market uncertainty meets the market well. Two examples, each from a very different type of network, yet having a similar shift in management structure triggered by decreasing market uncertainty, suggest the generality of this argument.
The next two chapters in this part are the case studies. First is email, then voice. The research leading to these chapters is from my Ph.D. thesis.
Email Case Study
This chapter presents a case study of the network-based service email, from its early days within the research community in the 70s through its stunning success in the late 90s, when the number of mailboxes grew to hundreds of millions in the United States alone. Initially, as many vendors competed for the dominant design, much experimentation occurred. Because market uncertainty was high at that time, this experimentation was of great value. When Internet email won and the standards stabilized, the popularity of more centralized email services such as Hotmail grew. Roughly 40 million more mailboxes currently exist for centralized email services than the more distributed (and traditional) ISP-based email systems. This case illustrates the relationship between market uncertainty and management structure — when market uncertainty was at its highest in the 80s, the value of experimentation caused the distributed management structure to work best. Later, as the maturity of the technology caused market uncertainty to decrease, the value of the centralized management structure overcame the advantage of end-2-end architecture. The emergence of a dominant design and stable standards indicates this reduction in market uncertainty. The history of email as presented in this case fits the theories of this book well.
The theory presented in Part One predicts the evolutionary pattern of email in the context of the standards that became accepted  and the
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way the implementation of these standards unfolded in light of market uncertainty. At first, market uncertainty was high; many competing email architectures existed with both centralized and distributed management structures. Each vendor offered a different feature set, allowing customers many choices among different email services. As this theory predicts, when market uncertainty was high, distributed architecture was more popular; as market uncertainty decreased, users migrated to a more centralized management structure. As this theory also predicts, the ultimate winner of the game (IETF Internet email) allows both distributed and centralized implementations of the standards, thus enabling it to prosper in any environment. Internet email is the architecture that allows the most experimentation due to its end-2-end nature, the openness of IETF specifications, and the modularity of those specifications.
There have been several different generations of email, as depicted in Table 8.1, with each generation influencing the services and architecture of the next generation. The rows of this table are the attributes of the email systems that existed in the particular generation. In the research generation, academics experimented with email service. Then, in the geek generation, email became popular with technical professionals exchanging messages. Next, in the business generation, the business community discovered that email could speed the flow of information and cut transaction costs. Finally, email became a way for the average person to communicate in the masses generation.
Table 8.1 High-Level Email History
RESEARCH GEEKS BUSINESS MASSES
GENERATION (70S) (80S) (90) (95)
Systems IETF, OSI IETF, OSI, AT&T, MCI, IETF
Post Office IETF, OSI,
(many other proprietary