FDDI - Elasticity buffer and smoother function
Each point-to-point link is clocked by the Tx node. Stations can have different clock rates ?f < 0.01 %. Insert IDLE preamble symbols. At least 16 IDLE before each frame. Elasticity buffer in other stations may change the length of the IDLE pattern. E-buffer is a FIFO which is filled half way before bits are removed. This requires pointer control in the FIFO.
Need to compensate for E-buffer deleting too many symbols from the same preamble. Unconstrained preamble shrinkage can result in loss of frames. Smoother function absorbs surplus symbols from longer preambles and redistributes them into shorter preambles. Smoother comes after E-buffer in each station.
Because this is a distributed algorithm for a statistical process it is very hard to test.
DEC implemented a 200 node ring in hardware to prove the smoother function.