RE: [802.3af] clocking over Ethernet
Gentlemen:
The work of this group is limited by the "Scope" and
"Purpose" of the PAR for P802.3af:
=================================================
6. Scope of Proposed Project
Define methodology for the provision of power via balanced cabling
to
connected Data Terminal Equipment with 802.3 interfaces. The amount of
power
will be limited by cabling physics and regulatory considerations.
Compatiblity
with existing equipment will be considered.
7. Purpose of Proposed Project:
To provide power for a new class of devices with 802.3 interfaces enabled
by
progress in silicon technology. These devices are characterized by low
power
requirements and LAN connectivity.
=================================================
Your proposals go well beyond these limits and, rather than being a
benign add-on to existing twisted-pair Ethernet, would be a radical
change to the entire asynchronous nature of Ethernet as it currently
exists. It is very clearly not an appropriate addition to the current
project. for P802.3af which is about power.
If you feel that trying to add synchronous timing to Ethernet networks is
an appropriate proposal for an amendment to the IEEE 802.3 Standard then
the proper method for pursuing this is found at:
http://www.ieee802.org/3/rules/rules.html
See section 7.1
At best, such a project would only give you timing control within
Ethernet links and across Ethernet MACs. The transit time of information
across Ethernet switches and routers is completely outside the scope of
IEEE 802.3.
Please move this discussion to another venue.
Sincerely
Geoff Thompson
|================================================|
| Geoffrey O.
Thompson
|
| Chair IEEE
802.3
|
| Nortel Networks, Inc. M/S
SC5-02
|
| 4401 Great America
Parkway
|
| P. O. Box
58185
|
| Santa Clara, CA 95052-8185
USA
|
| Phone: +1 408 495
1339
|
| Fax: +1 408 495
5615
|
| E-Mail:
thompson@xxxxxxxx
|
| Please see the IEEE 802.3 web page
at |
|
http://www.ieee802.org/3/index.html
| To download your FREE copy of Std. IEEE 802.3 |
|
http://standards.ieee.org/getieee802/802.3.html
At 02:56 PM 7/31/01 +0100, Tony Bayley wrote:
I would also like a method of achieving
synchronisation to a few
microseconds via ethernet. However The power supply in power over
MDI
is not a good way to distribute timing information. Typically only
the
devices at the very edge of the network will be powered via MDI.
The
hubs, switches, etc nearer the network core are unlikely to be
powered
via MDI, so the network-edge powered-devices will be in discrete
groups
clustered around their own PSE, with no universal power over MDI
connectivity between them. Timing information distributed along
with
power over MDI, in this scenario, would only allow synchronisation
of
the PDs attached to a single PSE, and would not be scalable to
larger
networks.
Tony Bayley
Principal Hardware Engineer
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-----Original Message-----
From: owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
[mailto:owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx]
On Behalf Of
Raymond Gass
Sent: 31 July 2001 08:47
To: Steve Jackson; WM
Cc: stds-802-3-pwrviamdi@xxxxxxxx
Subject: RE: [802.3af] clocking over ethernet
Steve,
the problem I see with NTP is jitter and wander that makes
it not really appropriate to generate a sync pulse
I like the proposal from Joerg; should be investigated
regards
Raymond
-----Message d'origine-----
De : owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
[mailto:owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx]De
la part de
Steve Jackson Envoyé : lundi 30 juillet 2001 14:49 À : WM Cc :
stds-802-3-pwrviamdi@xxxxxxxx
Objet : Re: [802.3af] clocking over ethernet
Joerg
Your application may be best served by using the Network Time
Protocol
(NTP).
It is fairly inexpensive to implement a small NTP client in
Ethernet
devices, and getting cheaper.
You may wish to look at this comprehensive URL:
http://www.eecis.udel.edu/~ntp/
and also read the archives at the Usenet newsgroup:
comp.protocols.time.ntp
regards
Steve Jackson
* * *
WM wrote:
>
> Hello together,
>
> sorry for dissturbing. I know that this is maybe not the right place
> to ask
> for it but maybe here are the right people to give me a helpful
> answer. In principle it could be also a nice add on for
802.3af.
>
> Power over MDI is what we are looking for for several years and it
is
> a must for several applications like VoIP phones etc. but to fully
> utilize and replace ATM, ISDN or other media by ethernet I think at
> least for migration a way to synchronize devices would be usefull.
An
> independent clock source like GPS is not usefull in our application.
> Is there any way to clock or at least sync devices on the ethernet?
> One way
> would be to use e.g. the link pulses but switches don´t guarantee
that
> all ports are in sync. The power supply in power over MDI would also
> be a way to add a sync pulse.
> Many thanks in advance for your comments.
>
> Best regards
> Joerg
>
> --------------------------------------------------
> Wilhelm Mikroelektronik GmbH
http://www.wilhelm.de
> Sueggelstr. 31 - 44532 Luenen
- Germany
> phone ++49 2306 928280 fax: ++49 2306 928289
>
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