Why it is necessary to put two 120 ohm termination resistors at each end of CAN transmission line respectively? Does it make an equivalent resistance of 60 ohm? (parallel resistors). Is it OK to put only a single resistor at any end or in middle of this transmission line?
If you want to avoid data reflections from either end of the cable you'll need to terminate those open ends in the characteristic impedance of the cable. As far as reflections are concerned the two impedances are not in parallel. At DC they are but at data transmission edge speeds they are not.