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- krish.vedam
February 13, 2007, 4:02 am
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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.
2. 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.
Re: collision happening when crc is transmitted by the transmitter
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.
Re: collision happening when crc is transmitted by the transmitter
krish.vedam@gmail.com wrote:
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
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