Re: [EFM] Network timing?
Geoff,
I agree wholeheartedly that any form of guaranteed latency or synchronous behavior
is outside the scope of 802.3ah.
However, if there are some PHY candidates that might allow such behavior and others
which preclude it - the group may take that into account when weighing the options.
The specification of any form of synchronous behavior may be left to vendors or it
may be defined by another body as a standard to be applied over an 802.3ah Ethernet
link.
Hugh.
Geoff Thompson wrote:
> Matthew
>
> This is not possible within the Scope of the P802.3ah project
> The project is for physical layers.
>
> There is no concept of guaranteed latency across the MAC or between ports
> of a bridge (switch) in 802.3 and 802.1 Standards.
>
> Ethernet networks are not synchronous.
>
> That is not to say that some vendors may not provide some latency specs in
> their products.
>
> Geoff
>
> At 04:04 PM 9/26/01 +1000, Beanland Matthew wrote:
>
> >Hi EFMers,
> >
> >I guess this is a question for the service providers out there. Imagining an
> >EFM ONU supporting bearer emulation (say, in order to provide E1/T1 interfaces
> >for connection to a legacy PABX), is there any interest in having the OLT
> >propagate network timing (usually 8kHz, traceable back to some reference) to
> >the ONUs by some method?
> >
> >Propagation of network timing is allowed for in the xDSL standards.
> >
> >Should we require propagation of network timing in EFM it could be propagated
> >by either the Ethernet symbol rate itself or via some coding method. Some
> >physical layer schemes (ATM25 comes to mind) use a low spec oscillator for the
> >line rate and insert special line tokens at 8kHz to allow user side equipment
> >to recover network timing if required. It would be possible to use one of the
> >non-data 8B/10B tokens as a timing marker and send at 8kHz, alternatively if
> >there is an OAM block it could be sent at 8kHz rate.
> >
> >Best Regards,
> >
> >Matt
> >
> >Matt Beanland, Project Manager/Principal Architect
> >Telecommunications Research and Development, Fujitsu Australia Ltd
> >5 Lakeside Drive, Burwood East 3151, Victoria, Australia
> >e-mail: matthew.beanland@xxxxxxxxxxxxxx Phone: (613) 9845 4313