Two notions of bandwidth are arising, said Stephen Alexander, chief technology officer of Ciena Corp. (Linthicum, Md.). Infrastructure bandwidth is the type of static bandwidth telecom service providers have long dealt with. But the use of virtual-circuit technology and Internet Protocol (IP) flow-management methods has created a "service bandwidth" that can be controlled dynamically by carriers, with some tools placed directly in the hands of end users, Alexander said.

The key factor in choosing the network equipment for topologies of the future, he said, is to "decouple the notion of service bandwidth from infrastructure bandwidth and consider the two as separate issues."

Stewart Personick, professor of communications at Drexel University in Philadelphia, said that the intrusion of IP-centric switch and router manufacturers into telephony backbones was supposed to signal the end of circuit-switched services. Instead, those vendors are promoting such concepts as multiprotocol label switching (MPLS) and its optical cousin, multiprotocol lambda switching, to create nailed-up IP flows that look a lot like circuits.

"I think we will see the evolution to circuit-switching or capacity-switching capabilities in the core network," he said.

Despite the turn to OC-192 (10 Gbits/second) and OC-768 (40 Gbits/s) and the simultaneous use of greater numbers of dense wave-division-multiplexed channels, there will be no glut of bandwidth on the market, Personick said.

Every trick in the book

New applications like Napster are driving up demand, and users stay connected longer. Optical equipment developers will have to use every trick in the book to break through the "1-bit-per-hertz" barrier, he said.

Alexander held out hope that there are still many areas in which such gains can be achieved. More use of forward-error-correction algorithms in optical networks could lead to significant improvements in performance, the Ciena executive said.

"People fight over tenths of a decibel, and here's 5 or 6 dB just staring us in the face," he said.

Alexander suggested to the carrier-oriented crowd that 10-Gbit Ethernet may end up being the framing and transport standard to unite WANs of several sizes in several nations.