 systems have very well-developed business processes and techniques for managing their environments. But the various systems' databases still do not always speak to one another to give one comprehensive view. In the IP world, the operational support systems are relatively new and are generally no more inte- grated than those found in the PSTN. The backbone of the traditional PSTN was largely based on a generation called the Plesiochronous Digital Hierarchy (PDH), which includes the T-carrier, E-carrier, and J-carrier standards, depending on the country the system is deployed in. The local loop of the PSTN was provisioned as a twisted-copper-pair analog subscriber line. The PSTN Infrastructure Service Providers Many abbreviations and acronyms are used to define the various players and the parts of the network in which they play. Some telcos can and do fulfill more than one of these functions, depending on the policy, regulatory, and licensing condi- tions that prevail in the area. The following terms are largely used in the United States, but they are important to the discussion in this chapter because they illus- trate the functions service providers are addressing: PTO-PTO stands for public telecommunications operator, which is the name for an incumbent carrier in places other than the United States. Often, these are government owned or controlled. In some countries, the more proper term is PT&T, for post, telegraph, and telephone. VAN provider-VAN stands for value-added network. The term VAN pro- vider originated around 1970 and was applied to companies competing to provide telecommunications services, specifically with offerings focused on data communications and data networking. VANs provided more than a simple pipe from point A to point B. They provided some additional intelli- gence in the network, to, for example, perform error detection and correc- tion, or to convert protocols or languages that different computers speak so that you could have interoperability across the network. Value-added ser- vices (V