Long-term studies of the Internet back up Cerf's assessment. At Stanford University, the International Committee for Future Accelerators has been tracking Internet performance and reliability for several years. Its tests show that the global reliability of the Internet has been improving by 40 percent to 50 percent annually, while performance has increased at an annual rate of 10 percent to 20 percent.

Even carriers acknowledge the growing role of the Internet. "Performance on the Internet is great," says Stu Elby, vice president of network architecture and enterprise technologies at Verizon Communications Inc. in New York. "You see more and more business being conducted over the Internet because it's more reliable."

But the Internet still can't deliver for critical applications that require a guaranteed QoS, and it doesn't offer the same level of security as private network services, Elby says. Users agree.

"What we haven't gotten is services and features such as QoS. That's our motivation for building private infrastructures," says Hill. Boeing is well into a massive project to re-create its global private network services built on Multiprotocol Label Switching (MPLS) technology. Carriers use the IP-based network service to tag and logically separate IP traffic into secure virtual private networks for different corporate clients, as well as to route traffic using the shortest possible path. Service providers see an MPLS-based infrastructure as a consolidation platform that lets them efficiently deliver all traffic types, including voice, video and data.

Whether the Internet will overcome current limitations is a matter of fractious debate. Telecommunications carriers play up the Internet's weaknesses, which they claim are inherent in its connectionless, best-efforts delivery architecture. "We believe a [QoS] Internet mechanism is almost impossible," says Chae-Sub Lee, chairman of the Focus Group on Next Generation Networks at the International Telecommunication Union.