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RE: [802.3af] clocking over ethernet

I would also lke 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

Tony Bayley
Principal Hardware Engineer

Bluesocket Limited
Jellicoe House
Botleigh Grange Office Campus
Grange Drive
Hedge End
SO30 2AF
United Kingdom

email:  tbayley@xxxxxxxxxxxxxx
Tel:  +44 (0) 1489 773983
Fax:  +44 (0) 1489 773966

-----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


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



-----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


Your application may be best served by using the Network Time Protocol

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:

and also read the archives at the Usenet newsgroup:



Steve Jackson

* * *

WM wrote:
> Hello together,
> sorry for dissturbing. I know that this is maybe not the right place 
> to
> 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
> 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
> Many thanks in advance for your comments.
> Best regards
> Joerg
> --------------------------------------------------
> Wilhelm Mikroelektronik GmbH
>    Sueggelstr. 31  -  44532 Luenen  -  Germany
>   phone ++49 2306 928280  fax: ++49 2306 928289
> --------------------------------------------------