lowest-cost to platinum service, with the highest QoS resulting in the highest cost. Where there is a difference between the PSTN and the Internet is that in the 1980s, the PSTN took the approach of deploying ATM to support multimedia and QoS. Interestingly, the telco community is now looking toward one of the newer standards developed by the IETF, MPLS, as a means of reducing some of the costs traditionally associated with ATM. (MPLS is covered at the end of this chapter.) The ultimate goal, at least based on what we know today, is to marry IP and the optical realm via a control plane based on a more robust version of MPLS called Generalized MPLS (GMPLS). The Internet has the same objective as the PSTN: to support high speeds, accommodate multimedia traffic, and support QoS guarantees. But the Internet community took a slightly different approach than the PSTN. Rather than rely on ATM and its QoS architecture, it began developing various architectures that address class of service (CoS) and QoS. Included in these is an overall umbrella architecture known as Integrated Services Architecture (ISA). ISA encompasses various solutions, including IntServ and DiffServ, along with MPLS; these strategies have the ultimate goal of blending IP and optical and migrating to GMPLS. Convergence in the Service Environment An important perspective of convergence lies in the operating assumptions of both service providers and enterprises. Let's look at both the traditional assumptions and current thinking. Traditional Operating Assumptions In the service environment, the operating assumptions are those of the traditional carrier mindset. Much of the carrier's business operations have been driven by industry regulations. Voice is a regulated environment, whereas data is not, and because more than 70% of carrier revenues come from voice, most of the tradi- tional carrier's attention has been focused on that world. For example, network engineering has been focused on the requirements of voice traffic, and the network has been optimi