ly available for 5 cents a minute or less. International rates are dropping as well. It is difficult to make a busi- ness case for developing VoIP on the Internet when competitors with infrastructure al- ready in place have such low costs. Another challenge to the business case for VoIP on the Internet is the historical un- reliability of the Internet. The Internet is becoming more reliable, but this is more the result of overprovisioning capacity than it is the result of improvements that define QoS at the network layer. If vendors overprovision capacity and, based on this, guar- antee QoS, this may help with the business case. However, this option to some extent means that VoIP is working but that it is not creating greater efficiency in the use of transport capacity. With all of this, two key facts remain. First, the Internet is used for many things, and demand for its capacity is shared among these functions. Without im- proved management of the network supporting defined QoS, it is difficult to ensure support for time-sensitive voice and video services. Second, the Internet is more vul- nerable to attack than the PSTN. As a result, the system a VoIP on the Internet provider is relying on (and trying to sell to venture capitalists) is not under the control of the provider that must guarantee quality to its customers. Investing in VoIP on the Internet might seem like investing in a competitor for Greyhound Bus Lines that plans to save money by using bicycle repairmen instead of licensed mechanics. The third challenge to the business case comes in the form of other, more robust plementations of VoIP. We will discuss some of these in the next subsection. 19.4.2 VolP on the PSTN The problem with VoIP on the Internet is not VoIP, it is the Internet. The most likely place for VoIP long-distance and even local services to appear as a viable business ser- vice is on the PSTN itself. As of summer 2002, Lucent Technologies, Cisco, Nortel, and Avaya are selling PSTN switches supporting VoIP. In the PSTN, the physical in