On determining the optimal optical reach for a long-haul network

Systems that enable optical bypass, where traffic transiting a node can remain in the optical domain as opposed to undergoing costly optical-electronic-optical (O/E/O) conversion, are gradually being accepted in carrier networks. An important factor in determining the cost effectiveness of such systems is the optical reach, the distance an optical signal can travel before needing to be regenerated. Longer optical reach results in a smaller number of required regenerations and hence less equipment and lower operating costs. In order to achieve longer reach, however, more expensive equipment such as amplifiers and transponders is typically needed. As the optical reach continues to increase, the cost benefit provided by reduced regeneration is eventually offset by the more expensive system equipment, leading to a concave curve of total network cost versus optical reach. This paper describes the analysis of four representative North American long-haul networks over a range of assumptions to determine the optimal optical reach from a cost perspective. In such networks, an optical reach in the range of 2500-3500 km yields the minimum, or close to the minimum, total capital cost over a wide range of assumptions, while representing a good tradeoff between decreased operating costs and increased initial network cost.