RE: [802.3af] clocking over Ethernet
I agree with you 100%. I know that clocking is in principal out of scope of
802.af but please let me just finally clarify the reason for asking in more
detail. I would really appreciate if the discussion could be continued at
another place. I´m open for suggestions. Please write directly to me.
802.af will be a reason for customers to make changes in their network
infrastructure. These changes over time will be probabbly even major
changes in some places since 802.af enables completly new applications.
Soon we will see cheap 802.af solutions and this means:
802.af makes it possible to replace industrial busses (profibus/interbus
etc.) by powering sensors/actors, ISDN (by powering phones/gateways) and
propriatary communication/control interfaces.
In my opinion it is even an good alternative (and I know that some consumer
electronic companies work on it) to IEEE1394. I know that 1394 has another
focus but putting a CAT-5 network is somewhat easier than planning a
flexible 1394 network (in Europe we don´t have phone nets like in the US).
My house and several of friends have CAT-5 networks at home and I run TV,
audio, phone, alarm system, light/heat control through it.
That ethernet is async is no problem in most applications and I never
intended to change it to isochronous. I just looked for a way to add a sync
signal while keeping COMPATIBLE with existing DTEs.
The precision I look for is in the sub us or better ns range. This would
enable to sync e.g. mobile phones. It would enable plug and play mobile
(e.g. DECT) networks with support of seamless handover/roaming. Just plug
the basestations into sockets of a synced net. The syncing would improve
radio spectrum use (you wrote that). There are many other applications that
would also benefit from synchronising. Agaoin: the ethernet data transfer
can be kept async.
802.af is a reason to develop new switch controllers/PHYs with integrated
support for 802.af. Since there won´t be many further generations of
ethernet this is maybe the last and final chance to introduce sync signals.
A sync enabled DTE could send a round trip signal through two connected
wires like +/. wires: through + to central point and through - back. With
defined transformer parameters it should be possible to measure line length
in order to calculate the delay to have highest possible precision (this
happens once during DTE initialisation). The only thing missing then is a
sync pulse sometimes (once a second is absolute sufficient) from the hub.
The exact clock I can generate in the DTE locally. A sync on the power
avoids any requirement to change ethernet PHYs. A 0.5/0.2 Volt pulse that
is inside the tolerances of 802.af would maybe sufficient. A simple
protocol could seperate noise from sync pulses. I´m open for other ideas.
But I think there could be a way that can coexist with existing equipment
and still keep the chance for that feature.
802.af sync would also enable to add power hubs AND sync for mid span
application without removing eventually expensive switches completly.
caporis networks AG * Germany
At 10:05 01.08.01 +0200, Raymond Gass wrote:
> 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 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 -----Message d'origine-----
> : Bob Bell [mailto:rtbell@xxxxxxxxx]
> : mardi 31 juillet 2001 22:32
> : 'Geoff Thompson'; 'Tony Bayley'; 'Raymond.gass'; 'WM'
> : stds-802-3-pwrviamdi@xxxxxxxx; 'Tony Jeffree'; bob.grow@xxxxxxxxx;
> : RE: [802.3af] clocking over Ethernet
> - 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 -----Original Message-----
>[mailto:owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx]On Behalf Of
>Sent: Tuesday, 31 July, 2001 11:01 AM
>To: Tony Bayley; Raymond.gass; 'WM'
>Cc: stds-802-3-pwrviamdi@xxxxxxxx; Tony Jeffree; bob.grow@xxxxxxxxx;
> davel@xxxxxxxxxxxx; David_Law@xxxxxxxxxxxxxx
>Subject: RE: [802.3af] clocking over Ethernet
>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
>will be limited by cabling physics and regulatory considerations.
>with existing equipment will be considered.
>7. Purpose of Proposed Project:
>To provide power for a new class of devices with 802.3 interfaces
>progress in silicon technology. These devices are characterized by low
>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:
>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.
>At 02:56 PM 7/31/01 +0100, Tony Bayley wrote:
> I would also like a method of achieving synchronisation to a few
> However The power supply in power over MDI
> Typically only 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
>clustered around their own PSE, with no universal power over MDI
> 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
>Principal Hardware Engineer
>Botleigh Grange Office Campus
> +44 (0) 1489 773983
> +44 (0) 1489 773966
>[mailto:owner-stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx] On Behalf Of
>Sent: 31 July 2001 08:47
>To: Steve Jackson; WM
>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
>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 :
>Objet : Re: [802.3af] clocking over ethernet
>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:
>* * *
>> Hello together,
>> sorry for dissturbing. I know that this is maybe not the right
>> 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
>> 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
>> independent clock source like GPS is not usefull in our
>> 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
>> all ports are in sync. The power supply in power over MDI would
>> be a way to add a sync pulse.
>> Many thanks in advance for your comments.
>> Best regards
>> Wilhelm Mikroelektronik GmbH http://www.wilhelm.de
>> fax: ++49 2306 928289
Wilhelm Mikroelektronik GmbH http://www.wilhelm.de
Sueggelstr. 31 - 44532 Luenen - Germany
phone ++49 2306 928280 fax: ++49 2306 928289