1000BaseT ethernet

1000BaseT ethernet

Post by w » Mon, 30 Jun 2003 02:37:09



Hi,

2 questions:

1.standard registers - when working with mii, you can query your
transceiver (after auto-nego for example) using standard mii registers
in a way that replacing to another vendor's transceiver in your
machine, won't require software change at all.
Are there standard regs for the whole gmii information as well (so
that I won't have to use vendor's proprietary regs and be
vendor-dependent in auto-nego process for example...)?

2.suppose my machine has 1000baseT port. is there a 'real-world'
practical need to support low rate configurations (10/100hdx
10/100fdx)? Isn't the fact that someone at the other end of the link
call me implies that he uses a 1000BaseT port as well?

thanks,
wd.

 
 
 

1000BaseT ethernet

Post by Rich Seifer » Mon, 07 Jul 2003 08:42:53




> 2.suppose my machine has 1000baseT port. is there a 'real-world'
> practical need to support low rate configurations (10/100hdx
> 10/100fdx)? Isn't the fact that someone at the other end of the link
> call me implies that he uses a 1000BaseT port as well?

If you don't support any alternate configurations, then your system will
either operate at 1000 Mb/s or not at all. What if the device is
sometimes used with a 100 Mb/s hub/switch and sometimes with a 1000 Mb/s
switch? In the "real world", you generally can't assume that a user has
completely migrated to 1000 Mb/s; many times the device must be capable
of 100 Mb/s operation (or perhaps even 10 Mb/s).

--
Rich Seifert              Networks and Communications Consulting

(408) 395-5700            Los Gatos, CA 95033
(408) 395-1966 FAX

 
 
 

1000BaseT ethernet

Post by w » Mon, 07 Jul 2003 21:01:48


Thanks for the answer!
In this matter, If I work in A/N mode and the other side is being
forced to some configuration, I assume the phy will detect the correct
speed of the other side, but can the MAC find out about that speed
from the PHY registers? my MAC layer need to know whether it works
with 10/100 or 1000 (2 different code blocks), and the advertisment
register is valid only when the other side A/N with me(or am I
wrong?)...

thanks.




> > 2.suppose my machine has 1000baseT port. is there a 'real-world'
> > practical need to support low rate configurations (10/100hdx
> > 10/100fdx)? Isn't the fact that someone at the other end of the link
> > call me implies that he uses a 1000BaseT port as well?

> If you don't support any alternate configurations, then your system will
> either operate at 1000 Mb/s or not at all. What if the device is
> sometimes used with a 100 Mb/s hub/switch and sometimes with a 1000 Mb/s
> switch? In the "real world", you generally can't assume that a user has
> completely migrated to 1000 Mb/s; many times the device must be capable
> of 100 Mb/s operation (or perhaps even 10 Mb/s).

 
 
 

1000BaseT ethernet

Post by Rich Seifer » Tue, 08 Jul 2003 07:17:04




> In this matter, If I work in A/N mode and the other side is being
> forced to some configuration, I assume the phy will detect the correct
> speed of the other side, but can the MAC find out about that speed
> from the PHY registers?

A standards-compliant, Auto-Negotiating device will properly detect the
speed of its link partner regardless of whether the partner is using A-N
or is manually configured. However, it is NOT possible to determine the
duplexity of a link partner without both sides advertising their
capabilities. If your link partner is manually configured to
full-duplex, your Auto-Negotiating end will not be able to detect this;
the default is for the A-N device to assume half-duplex (the safest
option), and you will have a duplex mismatch.

For this reason (and others) it is generally NOT a good idea to manually
configure anything. Let Auto-Negotiation do its job. If you want to
restrict the possible modes of operation, set the A-N adverti*ts to
reflect only those outcomes that you are willing to accept; do NOT just
set your device to the desired outcome.

Your driver can always interrogate the PHY registers to determine when
A-N has completed, and what the resulting configuration is.

Quote:> my MAC layer need to know whether it works
> with 10/100 or 1000 (2 different code blocks), and the advertisment
> register is valid only when the other side A/N with me(or am I
> wrong?)...

Regardless of whether the other side is using A-N or not, once your own
A-N completes (including parallel detection), the PHY registers should
indicate the resulting configuration.

--
Rich Seifert              Networks and Communications Consulting

(408) 395-5700            Los Gatos, CA 95033
(408) 395-1966 FAX