RE: [802.3af] clocking over Ethernet
Bob,
I
remember 802.9. The situation here is a little bit different. We are not
necessarily trying to build
isochronous services over ethernet. Let's take an
example: you connect a DECT or PWT base
station to your LAN. The base station is remotely
powered according to 802.3af
Now,
if you don't want to lose timeslots and thus traffic on your base stations, they
need to be
synchronized. They need a reference for the start of
the frame otherwise slots will be lost
in the
area covered by 2 or more stations (which is needed by essence if you wish
to
handle
handover properly)
The
first solution is to bring new wires to carry sync from a central point to all
base stations.
Then,
you lose benefit of reusing existing LAN wiring. Not a good
proposal
The
second solution: GPS. Nice but problems indoor
Third
proposal, NTP: does not work due to transmission time
dispersion
The
proposal from Joerg is quite good: you have phantom pairs to carry power, why
not add
a SYNC pulse on this phantom? Of course, you need
to understand how to cross intervening
nodes.
Those
equipment that do not need power or SYNC are not affected (which was
not
the
case in .9). There is no change to the existing asynchronous nature of Ethernet
as
it
currently exists.
Equipment that just need power, according to .3af
should not be disturbed by the SYNC pulse
Only
equipment that need SYNC or Power and SYNC will use it. Other equipment are
not
affected at all
By
doing this, you bring new requirements on 802.3af. This might be an extension of
the existing PAR
or a
new PAR. But at least, initial discussion should take place in
.3af
Raymond
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
>
>
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Mikroelektronik GmbH http://www.wilhelm.de
>
Sueggelstr. 31 - 44532 Luenen -
Germany
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