Faced with the many challenges of running a network, capacity planning, increased service needs, fiber depletion, and layered bandwidth management, the carriers need options to provide an economical capacity to withstand the onslaught of demand. One way to increase the fiber capacity is to lay more fiber. Where the cost of laying new fiber is minimal, this becomes the better solution. Unfortunately, laying new fiber will not necessarily enable service providers to provide new services or use the bandwidth management capability of a unifying optical layer.

A second choice is to increase the bit rate using TDM. Traditionally, this has been the carriers choice (DS-1, DS-2, DS-3, and so on). However, when the carriers use this approach exclusively, they must make quantum leaps in one step, so they do not have to do this on a regular basis. This leads them to buy more than they initially need. Based on the SONET hierarchy, the next incremental step from OC-192 is OC-768 (10 to 40 Gbps). This method has been used with various networks based on SONET or SDH. Regardless of the location or technology, the carriers are making large investments in their infrastructure.