Siemens SCALANCE X-200 Series Compact Operating Instructions page 103

Note
The following applies to IE Switches X-200 that do not have IRT functionality:
The number of IE Switches X-200 connected in a line influences the frame propagation time.
When a frame passes through an IE Switch X-200, it is delayed by the Store&Forward
function of the IE Switch X-200
 with a 64 byte frame length by approx. 10 microseconds (at 100 Mbps)
 with a 1500 byte frame length by approx. 130 microseconds (at 100 Mbps)
This means that the more IE Switch X-200 devices the frame passes through, the longer the
frame delay.
Note
The following applies to IE Switches X-200 that have IRT functionality:
The number of IE Switches X-200 connected in a line influences the frame propagation time.
The more IE Switches X-200IRT a frame runs through, the higher the frame delay.
By using the "cut through" switching mechanism, the IE Switches X-200IRT are ideal to meet
the real-time requirements of PROFINET.
Cut through is not possible
 between a port set to 10 Mbps and a port set to 100 Mbps
 when two packets are to be sent at the same time on one port.
In this case, the IE Switch X-200 changes to Store&Forward and the delay increases.
SCALANCE X-200
Compact Operating Instructions, 12/2010, A5E00813159-11
Technical Specifications
7.1 Technical specifications
103