Can a standard NIC be triggered to send an electrical signal?

To my knowledge there is no standard configuration / feature for NICs to send any single pulses to the line when commanded.

With a normal 10Base-T Ethernet card normally when nothing is transmitted, the line is silent (only some link pulses could sent every now and then). When you transmit a packet, the Ethernet card sends a series of bits to the line presenting the data of the data packet.

So with such card you just need to send a packet, and the card sends a set of electrical signal pulses to the line... Any packet will do. With a TCP/IP networking send out ARP or UDP packet.

With 100 Mbit/s Ethernet (100Base-TX) things are not that simple.. When Ethernet card is transmitting data, you get bits on the line. But even when the card is not transmitting any actual data, there are bits traveling through the wire (a known bit pattern that keeps the data clocks on the oppostite ends of the link syncronized).

Say I write a program that creates a packet and inject it on the line. The packet will be sent as a set of electrical signal pulses to the line, as you say. What happens when they encounter an open circuit in the cable, do they get reflected due to the impedance mismatch? If the data is reflected, would it be too corrupted that my program won't be able to recognise it as the one it sent earlier?

------------------------------------- Tomi Holger Engdahl wrote:

##-----------------------------------------------##

Article posted with Cabling-Design.com Newsgroup Archive

comp.dcom.lans.ethernet - 3330 messages and counting!

##-----------------------------------------------##

Yes.

In 10Base-T ethernet system when the card sent out the pulse to the wire pair used ot transmit, and it hits an impedance mismatch, some part of the signal (or all) gets reflected back through that pair. When the reflected back signal reaches the card, it is coming to it though the transmit pair. There is no receiver on transmitting pair. The card does not know anythign about the signal being reflected on the cable.

##-----------------------------------------------##

Article posted with Cabling-Design.com Newsgroup Archive

comp.dcom.lans.ethernet - 3336 messages and counting!

##-----------------------------------------------##