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Latency for ethernet to ethernet
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rakeshm55:
Hi,
For a point to point 10/100 Ethernet connection what is the typical latency i can expect.
I am sending data between emac to emac
My scheme will be

DataA ---->EMAC_1---->PHY_1---->PHY_2---->EMAC_2 ----DataB

What can be the typical latency??  there is no network ... its a pint to point connection
The scheme is used for on board communication between two modules....I would like to quantify the processing delay that would be incurred while assing feom ethernet to ethernet
Yansi:
Propagation delay in the cable.

Plus the few clocks on top of that to process data through the PHY and MAC.
Rerouter:
If its for onboard communication. If you dont need isolation you could drop the phys and possibly the macs.
ejeffrey:
Propagation delay will always be less than the transmit time 100base/T.  Minimum frame size is 64 bytes plus 8 bytes for the preamble, which takes 5.76 microseconds to transmit.  Signal propogation for maximum size network link of 100 meters is only about 500 nanoseconds.  So unless you are chaining many switches together with maximum length cables you will never get close to 5 microseconds.

So delay to the MAC layer is probably dominated by receiving the full packet to evaluate the FCS.  There may be further delays depending on how you are getting the data: for instance, a USB to ethernet adapter would need to wait until the the next time the host requests data, while other buses support interrupts.
jbb:
There’s also approx 400ns delay for collision sense before transmit (yes even with full duplex :-( )
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