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Re: [EFM] Network timing?


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.


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 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