In order to prevent signal reflections on an unterminated transmission line, such as a stub, its line length must not exceed a maximum length. Here a typical rule-of-thumb suggests that the signal one-way trip time (the time it takes the signal to propagate from an actively driving node along the stub to the bus cable) should be shorter than 1/4 to 1/10 of the rise/fall time of the active driver. The equation shown on this slide, using a factor of 1/10, is used to calculate the various stub lengths for a range of transceivers with different data rates and rise/fall times for the signal velocities of an RS-485 cable and of 120 Ω impedance controlled PCB traces. In order to determine the maximum data rate or minimum bit-time, it is assumed that the driver rise/fall time is around 30% of the bit time: tr = 0.3 · tbit. With tbit = 1/DR follows > DR (bps) = 0.3/tr (s). The table clearly shows that with increasing data rates, and hence shorter driver rise/fall times, the maximum stub lengths reduce proportionally. Therefore, high speed applications always require short stub lengths. It is also the reason why daisy chaining is the preferred method in multipoint high speed data links.