Analysis of the performance of star, tree and mesh topologies is made for successive distance between the nodes at the bit rate of 15 Gbps . The number of users supported at different distances is calculated in terms of Quality Factor and BER for the input signal power of -40dBm. An optimized Hybrid Raman-EDFA amplifier is used for post amplificion. Mach-Zehnder modulator at extinction ratio of 30dB with symmetry factor of -1 is used for the modulation of signals. The spacing between the channels is taken as 0.1 THz with the line width of 1 MHz. It is observed that Star topology is capable to support more users than other topologies for a distance of 6Km in terms of quality factor and BER.