RE: [802.3af] clocking over Ethernet
Gentlemen -
If I
could speak from experience, IEEE 802.9b provided for a timing signal embedded
in the structure of the information flow. Even though we developed the standards
to a degree that was very implementable, the necessity of opening up everyone's
PC and installing a new NIC card made the transition to the 802.9 technology
unsalable. If you truly want to pursue that approach, reactivating 802.9 might
be the way to continue.
Bob
Bell
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
-----------------------------
Bluesocket
Limited
Jellicoe House
Botleigh Grange Office Campus
Grange
Drive
Hedge End
Southampton
SO30 2AF
United
Kingdom
email: tbayley@xxxxxxxxxxxxxx
Tel: +44 (0)
1489 773983
Fax: +44 (0) 1489 773966
www.bluesocket.com
-----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
>
--------------------------------------------------