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Ethernet auto-negotiate time

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Anonymous
September 11, 2004 11:19:36 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Hi,
I have been trying to calculate how long a successful Gigabit Ethernet
auto-negotiation sequence takes and the time I have calculated seems
to be quite high. From referring to the 802.3 standard:

Time [average] between consecutive FLPs: 16ms
Gigabit Ethernet uses 4 LCWs to auto-negotiate: one Base Page, one
message Next Page and two 1000BaseT unformatted Next pages.

Time to send four FLP: 4 X 16ms = 64ms

802.3 standards specify that each LCW should be received 3 times
before acknowledgement. Therefore, 4 FLPs [3 X LCW + 1 acknowledgement
LCW] are required for exchanging 1 LCW.

Therefore, minimum time to auto-negotiate 1Gbps link speed = 64 ms X 4
= 256ms

Considering that Ethernet is a LAN protocol, this seems to be too
large a vaue. Could somebody please tell me where I have made a
mistake? Thanks!

Chamara Gunaratne
pgunarat@csee.usf.edu
University of South Florida
Anonymous
September 12, 2004 12:01:56 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

In article <9155993e.0409111819.56653745@posting.google.com>,
pgunarat@csee.usf.edu (Chamara Gunaratne) wrote:

> Hi,
> I have been trying to calculate how long a successful Gigabit Ethernet
> auto-negotiation sequence takes and the time I have calculated seems
> to be quite high. From referring to the 802.3 standard:
>
> Time [average] between consecutive FLPs: 16ms
> Gigabit Ethernet uses 4 LCWs to auto-negotiate: one Base Page, one
> message Next Page and two 1000BaseT unformatted Next pages.
>
> Time to send four FLP: 4 X 16ms = 64ms
>
> 802.3 standards specify that each LCW should be received 3 times
> before acknowledgement. Therefore, 4 FLPs [3 X LCW + 1 acknowledgement
> LCW] are required for exchanging 1 LCW.
>
> Therefore, minimum time to auto-negotiate 1Gbps link speed = 64 ms X 4
> = 256ms
>
> Considering that Ethernet is a LAN protocol, this seems to be too
> large a vaue. Could somebody please tell me where I have made a
> mistake? Thanks!
>

No mistake, your numbers are right. Moreover, this is the *minimum* time
for a successful negotiation; in the event that an FLP burst is
corrupted, it may require more than 3 repetitions before acknowledgment
(but this is considered a rare event).

Given that Auto-Negotiation occurs just once at link initialization, it
is not considered a big deal to take a few hundred milliseconds. In
practice, this time overlaps with other events, such as machine boot
sequences, power-up self tests, etc., all of which take even longer.

By the way, the minimum negotiation time is less for lower data rates,
since the Base Page alone conveys all the necessary information to
negotiate 10/100 Mb/s operation.


--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 395-1966 FAX

Send replies to: usenet at richseifert dot com
Anonymous
September 13, 2004 2:18:25 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Thank you. I was not sure about the calculated time and am glad to
know that it is OK.

Gigabit Ethernet is now common in desktop computers and we find that
NIC power consumption is about 4% ~ 5% of the overall idle power
consumption of the computer. And with copper 10GigE NICs expected
within a couple of years that percentage is expected to increase
significantly. At the University of South Florida my advisor, Dr. Ken
Christensen and myself are studying the feasibility of dynamically
changing the link speed and hence reducing the power consumption of
the NIC. And the time taken to change link speed is an important
metric.

Thanks again for your kind response,

Chamara Gunaratne

Rich Seifert <usenet@richseifert.com.invalid> wrote in message news:<usenet-A7CF3C.08015512092004@news.isp.giganews.com>...
> In article <9155993e.0409111819.56653745@posting.google.com>,
> pgunarat@csee.usf.edu (Chamara Gunaratne) wrote:
>
> > Hi,
> > I have been trying to calculate how long a successful Gigabit Ethernet
> > auto-negotiation sequence takes and the time I have calculated seems
> > to be quite high. From referring to the 802.3 standard:
> >
> > Time [average] between consecutive FLPs: 16ms
> > Gigabit Ethernet uses 4 LCWs to auto-negotiate: one Base Page, one
> > message Next Page and two 1000BaseT unformatted Next pages.
> >
> > Time to send four FLP: 4 X 16ms = 64ms
> >
> > 802.3 standards specify that each LCW should be received 3 times
> > before acknowledgement. Therefore, 4 FLPs [3 X LCW + 1 acknowledgement
> > LCW] are required for exchanging 1 LCW.
> >
> > Therefore, minimum time to auto-negotiate 1Gbps link speed = 64 ms X 4
> > = 256ms
> >
> > Considering that Ethernet is a LAN protocol, this seems to be too
> > large a vaue. Could somebody please tell me where I have made a
> > mistake? Thanks!
> >
>
> No mistake, your numbers are right. Moreover, this is the *minimum* time
> for a successful negotiation; in the event that an FLP burst is
> corrupted, it may require more than 3 repetitions before acknowledgment
> (but this is considered a rare event).
>
> Given that Auto-Negotiation occurs just once at link initialization, it
> is not considered a big deal to take a few hundred milliseconds. In
> practice, this time overlaps with other events, such as machine boot
> sequences, power-up self tests, etc., all of which take even longer.
>
> By the way, the minimum negotiation time is less for lower data rates,
> since the Base Page alone conveys all the necessary information to
> negotiate 10/100 Mb/s operation.
Anonymous
September 15, 2004 6:42:59 AM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Chamara Gunaratne wrote:

> Thank you. I was not sure about the calculated time and am glad to
> know that it is OK.

> Gigabit Ethernet is now common in desktop computers and we find that
> NIC power consumption is about 4% ~ 5% of the overall idle power
> consumption of the computer. And with copper 10GigE NICs expected
> within a couple of years that percentage is expected to increase
> significantly.

I would think you could minimize the amount of circuitry
that had to be clocked at full speed during idle time.

For battery powered devices, though, I agree you want it
as low as reasonably possible.

-- glen
!