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
> as long as the out and back links have
> same delay-per-meter.
> 2) To do (1) might require a distinct physical
> which acknowledges the presence of
> links, rather than a broadcast
> 3) 802.17 may develop the protocols that implement
> 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
>although accurate network timing and good QOS are
>likely to be perceived as threats by IEEE 1394 zealots.
>David V. James, PhD
>Network Processing Solutions
>Data Communications Division
>110 Nortech Parkway
>San Jose, CA 95134
>> -----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
>> difficult at best.
>> I work for Peak Audio (part of Cirrus Logic), and
>> been using Ethernet for distribution of digital audio
>> over an Ethernet based network. The difference
>> us and "the other guy" is that we're doing 64+
>> 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
>> accuracy at 48 KHz over a 2 km wide Ethernet network.
>> We're actually getting better than that (1/10th
>> I think).
>> Here's a link to some CobraNet (that's what we call
>> stuff. It's somewhat audio-biased rather than
>> biased, and not very technical, but it might be at
>> a little informative.
>> That being said, I think we're getting off topic
>> If anyone has questions about this feel free to
>> me directly.
>> David Kessner
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