Re: [802.3af] nanosecond timing over Ethernet++
Are you refering to a implementation of Ethernet which has no
other Protocols involved (like IP)?
At 10:25 AM 7/31/2001 -0700, David James wrote:
>
>All,
>
>Relative to tight synchronization between stations,
>such as Ethernet speakers in the root.
>A couple points of interest:
> 1) Point-to-point connections have the capability
> of synchronizing devices at the
nanosecond level,
> as long as the out and back links have
about the
> same delay-per-meter.
> 2) To do (1) might require a distinct physical
layer,
> which acknowledges the presence of
point-to-point
> links, rather than a broadcast
bus.
> 3) 802.17 may develop the protocols that implement
(2).
> In concept, one could migrate 802.17
into the home.
>
>I think that the lack of a physical layer support would
>always limit the achievable worst-case accuracy.
>Statistical averaging isn't necessarily acceptable in
>high-fidelity audio, if the worst-case is orders
>of magnitude worse.
>
>I don't particularly favor placing the synchronizing
>pulse on the voltage supply, since power distribution
>has enough problems already. Some form of 802.3
>packet-signaling enhancements (supported by the MAC)
>seems more appropriate. Probably useful to the
customers,
>although accurate network timing and good QOS are
>likely to be perceived as threats by IEEE 1394 zealots.
>
>DVJ
>
>
>David V. James, PhD
>Chief Architect
>Network Processing Solutions
>Data Communications Division
>Cypress Semiconductor
>110 Nortech Parkway
>San Jose, CA 95134
>Work: +1.408.942.2010
>Fax: +1.408.942.2099
>Work: davidj@xxxxxxxxxxxxxxxx
>Home&Work: dvj@xxxxxxxxxxxx
>
>> -----Original Message-----
>> From: owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
>> Kessner, David
>> Sent: Tuesday, July 31, 2001 7:48 AM
>> To: stds-802-3-pwrviamdi@xxxxxxxx
>> Subject: RE: [802.3af] clocking over Ethernet
>>
>>
>>
>> > I would also lke a method of achieving synchronisation
to a few
>> > microseconds via Ethernet.
>>
>> Achieving that level of sync over a large network
is
>> difficult at best.
>>
>> I work for Peak Audio (part of Cirrus Logic), and
we've
>> been using Ethernet for distribution of digital audio
>> over an Ethernet based network. The difference
between
>> us and "the other guy" is that we're doing 64+
channels
>> of uncompressed real-time audio. This requires
>> synchronizing the audio sample clocks across the entire
>> network. Our spec says that we can get 1/4 sample
clock
>> accuracy at 48 KHz over a 2 km wide Ethernet network.
>> We're actually getting better than that (1/10th
sample,
>> I think).
>>
>> Here's a link to some CobraNet (that's what we call
it)
>> stuff. It's somewhat audio-biased rather than
timing
>> biased, and not very technical, but it might be at
least
>> a little informative.
>>
>>
>> That being said, I think we're getting off topic
here.
>> If anyone has questions about this feel free to
email
>> me directly.
>>
>> David Kessner
>> davidk@xxxxxxxxxxxxx
>>
*************************************
"People generally demand more respect for their own rights than they
are willing to allow for others"
James M. Polk
Consulting Engineer
Office of the CTO
Cisco Systems
18581 N. Dallas Parkway
Dallas, Texas 75287
w) 972.813.5208
f) 972.813.5280
www.cisco.com