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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:
>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.
>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
>> [mailto:owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx]On Behalf Of
>> 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

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