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collision happening when crc is transmitted by the transmitter

Iam presently involved in the design of a Gigabit wthernet mac. I know from the specification that any collision happening before 64 bytes is a normal collision. But the reason why Iam rising this question has to do with the transmitter hardware latencies in mind. I may be missing something here.

Let us think that we are transmitting a minimum sized packet(64 bytes) on the link.

1.Is it reasonable for the transmittter to not detect a collision that happened during crc transmission?

The reason is that according to the my present design there is every chance of my statemachine missing a collision during CRC transmission on the link.

  1. Is it always required that the JAM signal needs to be sent continous with the present packet collided(i.e tx_en needs to be continous).

Pleaese let me know your views.

Thanks in advance.

Reply to
krish.vedam
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If you are investigating collisions, the implication is that you will be dealing with Gigabit half duplex.

If I recall correctly, people on this newsgroup have been saying that there is no Gigabit half duplex equipment on the market. After all, with the distance limitations, people are pretty much going fully switched anyhow.

Reply to
Walter Roberson

I am sorry I didn't make it clear. The IP core design involves

10/100/1000 Mbps. So My question applies to even 10/100 Mbps case also.
Reply to
krish.vedam

As other posters have noted, there is little application for half-duplex Gigabit Ethernet. In the event you *do* want to support such functions, recognize that there is "carrier extension" in GbE, and collisions must be detected for the first 512 bytes, not just the first 64 as in 10/100.

That said, it is imperative that you detect collisions during the FCS transmission. Such collisions are "valid" (in the sense that they do not imply any faults in equipment or network configuration); a failure to detect collision during FCS would also mean non-compliance with the standard.

Then I strongly suggest that you redesign your state machine, or purchase one of the available, known compliant MAC cores.

Yes. Again, you should read the standard carefully, particularly the MAC behavioral formulation in Clause 4 (the Pascal code).

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Reply to
Rich Seifert

Dear Rich,

Thanks a lot for your feedback. I will handle the situatuon in the hardware accordingly.

Regards, Krish.

Reply to
krish.vedam

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