Intel 100BASE-TX manual Calculating Round Trip Collision Delay

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

Router

Stack of 100BASE-T hubs

400 m total network topology

521.6 m total network topology

with two collision domains

100BASE-TX

100BASE-TX

switching hub

transceiver

transceiver

switching hub

Up to 2 km

1 m

1 m

fiber cable

160.8 m

Stack of

(Full duplex)

Stack of

Stack of

100BASE-T

100BASE-T

100BASE-T

hubs

hubs

hubs

100BASE-T	100BASE-T Server	100BASE-T	100BASE-T
workstations	workstations	workstations	workstations
Domain 1	Domain 2	Domain 3	Domain 4
		100 meter Category 5 UTP
		160.8 meter fiber cable

5874.2

Interconnecting repeaters and switches in multiple domains

Calculating Round Trip Collision Delay

Calculating the round trip collision delay between all pairs of DTEs in a 100BASE-T network ensures that the network is not violating the CSMA/CD protocol. This calculation involves selecting the worst case path delay (PDV) to determine if your network falls within round trip collision requirements. The worst case path is usually the path between the two DTEs at the opposite ends of the network and the transmissions between them have the longest round trip time.

To qualify the DTE-to-DTE path in terms of worst-case delay, you must ensure that the maximum length fragment contains less than 512 bits after the start of the frame delimiter. To determine if the DTE-to- DTE paths fall within PDV requirements for a 100BASE-T network, calculate the delay values for the following network devices:

∙Link segment delay values (LSDV)

∙Repeater delay values

∙DTE delay values

∙Safety margin value

These values can be plugged into the following formula to calculate the worst case PDV for each path:

PDV = Sum of LSDVs + sum of repeater delays + DTE delays + safety margin

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