o that they auto- matically follow the tunnel to its egress.13 In the core, however, most existing high-bandwidth networks do not cur- rently switch packets. Instead, the bandwidth of the underlying optical fibers is allocated by either frequency-division multiplexing (FDM) (wave- length) or time-division multiplexing (TDM). NEs forward the data by switching particular time slots, wavelengths, or wavebands, or even the con- tents of entire fibers. This deterministic bandwidth allocation supports the guaranteed throughput for data and targeted QoS. The drawback of this approach is the overhead of the control traffic needed to set up and main- tain bandwidth allocations, and, for bursty streams, the potential waste when an application does not use all the bandwidth that was reserved. This last observation, however, needs to be tempered by two fundamental facts that are often ignored by proponents of packet technologies: (1) bandwidth Chapter 7 (at least in the long haul) has become a (relatively) inexpensive commodity, and (2) backbone traffic in a moderately to highly loaded network is not bursty when it contains traffic from thousands of sources and is processed by a chain of routers via speed-limited output ports (with deterministic ser- vice time). A simple application of the Central Limit Theorem on traffic flows comprised of not trivial (Web-, FTP-, and videostreaming-based) transactions will prove this assertion. In lieu of a Central Limit Theorem argument, researchers can take measurements in an actual moderately to highly loaded network and use the extensive body of techniques from the field of statistics known as goodness of fit and determine the distribution of the inter-router traffic.14 These points are not to be taken as a negative assessment of packet technology, but simply that these factors have to be properly taken into account when designing or pricing out backbone tech- nologies and architectures, and pitching these technologies against tech- nologies that are already deployed. MPLS proponents c