Intel 100BASE-TX manual DTE types Maximum round trip Delay value

A P P E N D I X B Intel Express 100BASE- TX Stackable Hub

NOTE

Media Independent Interface (MII) cables for 100BASE-T devices do not exceed 0.5 meters. These delay values are incorporated into the repeater and DTE delay values, therefore, it is not necessary to calculate the MII cable delay values separately.

2.Add the LSDVs for all the segments in the path.

3.Determine the delay for each repeater in the path.

Repeater delay values are specified in bit times. The default maximum repeater delay value for a Class 1 repeater is 140 bit times. There is a one repeater maximum for networks using Class I repeaters.

4.Determine the DTE delay values for the path.

DTE delay values are specified in bit times. The maximum DTE delay values for the different DTEs in a path are shown here:

DTE types	Maximum round trip
	delay value
Two TX/FX DTEs	100 bit times
Two T4 DTEs	138 bit times
One TX/FX DTE and	127 bit times
one T4 DTE✝

✝Worst case values are used (TX/FX values for MAC transmit start and MDI input to collision detect); T4 value for MDI input to MDI output.

5.Determine the appropriate safety margin for the path.

A safety margin of 4 bit times is recommended. This safety margin is used to provide additional margin to accommodate unanticipated delay elements in the path. If 4 bit times is not an appropriate safety margin for your path, you can choose between 0 and 5 bit times.

6.Insert the delay values determined using the calculations listed above into the following PDV expression:

Sum of LSDVs + sum of repeater delays + DTE delay + safety margin

If the PDV is less than 512 bit times, the path is qualified in terms of worst-case path delay.

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