The theoretical model used by Gigabit Ethernet to develop the optical physi
cal layer specifications is presented. The model calculates the penalties a
ssociated with using laser based transceivers on both multimode and singlem
ode fibre Gb/s links. Experimental verification of the model's predictions
is also presented along with discussion on the use of the model to predict
link performance. The model is generic to laser based fibre LAN links but s
pecific details and examples relevant to Gigabit Ethernet are discussed.