The network consists of 128 single wavelength (1550nm) hubs each producing 10 Gbit/s data with +10 dBm optical output power. These are each connected to 100 km of single-mode optical fibre with 0.2 dB/km attenuation and 15ps/km dispersion. After each 100 km fibre length, either a 20dB gain Erbium-doped fibre amplifier (EDFA) or a 20 dB gain electronic regenerator is provided. On the right-hand side, a 128 x 128 switch is provided which can be constructed from either 2 x 2 optical switches or designed as a classic 3-stage Clos optical switch. Gain may have to be provided within the switch. This is a realised as space switch initially, but it could be realised with time and space elements in a future upgrade. You are asked to do a basic design study by answering the multiple choice questions that follow.