Mitel SX-2000 Fiber Interface Module Part Number: 9400-200-301-NA Interfaces control node with DSU and peripheral nodes. Maximum Loop Resistance/Loop Lengths Maximum Permitted Loss in Fiber: -6 dB, using 62.5/125 μm optical cable with a numerical aperture of 0.275 inches. Maximum Length: -Approximately 1 km (0 to 5 km based on the sum of the cable loss and connector and/or splice losses. Total loss cannot exceed 6 dB.).