What is difference between Signal frequency and data rate
There is a mistake. The units of frequency is cycles/second and not Mbit/second. I noticed this mistake in one of the online links on CAN. 

I think what it means is  that the maximum theoretically possible data rate is 1Mbps and the typical real life maximum data rate is 320Kbps(40KBytes/sec). The standard says that for network lengths below 40m, 1Mbps can be achieved but for network lengths of 500m the data rate achieved is around 125kbps. So I think that's reason typical data rate is given as 40KBytes/sec.

References:


http://en.wikipedia.org/wiki/CAN_bus
http://www.computer-solutions.co.uk/info/Embedded_tutorials/can_tutorial.htm