Bus bandwidth is defined by the interface parameters and the stray parameters of SDA and SCL lines.
Not only the direct-current state of lines ("0" and "1"), but also the level difference ("0"→"1" and "1"→"0") are used in the signaling protocol of the bus. The presence of the stray parameters is characterized by droop of pulse which can disrupt the normal data exchange.
Another danger that can appear as a result of the use of too long conductors is connected with overstrain that may occur on the interface elements with significant quantities of stray inductance of wires.
In the process of experimentation and debugging circuits, usually when the microcontroller and the slave-devices are set on separate boards, the connections between them can not be made short. The breakdown voltage of the zener VD should be set 0.5 - 1 V more than level "1" on the SDA and SCL lines. Although such a method of protection is not found in the documentation for an obvious reason - professional developers have much more opportunities for the implementation of prototyping work, radio amateurs had better ensure that chips operate properly. The search for causes of a breakdown is a long and painful occupation connected with additional expenses, so be careful! You may not install the zener on a circuit board in a complete and streamlined design.
Now let’s consider the way of protection from high-voltage interference given in the original documentation. It’s important to know that this method is preferred in Hs-mode. According to the recommendations, protective resistors Rs are input in the circuit. To reduce the rise time of the synchronizing signal current source MCS is input in master device. SDA and SCL are called SDAH and SCLH respectively (letter “H” stands for “high” in the abbreviation).