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Re: SONET/Ethernet clock tolerance


Thank you for your comment, but I think I see some discontinuity 
between your recent replies to Rich and me.  It would be appreciated 
if you could help me to understand your point.

My understanding of your "a full fledged SONET compliant version" is 
preparing SONET Path STS-192c (with Path overhead) at 10GigE WAN-PHY. 
This sounds me that the clock compensation is performed by pointer 
manipulation (read it SONET re-framing) at ELTE, not by Idle frame 
deletion/insertion.  Note that the Ethernet side of ELTE should be 
considered as a part of Ethernet since there is no other "SONET-lite" 

My basic question is why you need SONET framing between WAN-PHY 
and ELTE.  This picture requires two SONET framers; one at WAN-PHY, 
and again at ELTE to full-SONET.  What's wrong if you prepare SONET 
Path STS-192c at ELTE? It will reduce the required number of SONET 
framer to only one at ELTE to full-SONET, and will reduce the overall 
implementation cost.  

In other words, why you force us to invest two specialized hardware for 
WAN access, WAN-PHY and ELTE, instead of one specialized hardware, 
SONET-compliant PHY or ELTE with LAN-PHY at Ethernet side?

Best Regards,

At 9:26 AM -0800 00.3.31, Paul Bottorff wrote:
> Rich:
> The 10 GigE WAN-PHY is asynchronous with standard Ethernet clock
> tolerances. The WAN-PHY has no SONET clock tolerance or jitter
> considerations. It is true that ELTE equipment (which is not part of
> Ethernet) needs to make a conversion into the SONET clock domain. Since
> this function is part of SONET equipment is only of academic concern to the
> IEEE. David's previous emails indicate how the SONET ELTE equipment may work.
> In the IEEE domain clock compensation may be performed by IDLE frame
> deletion/insertion. Idle frame deletion/insertion is supported by the
> <Length><HEC> delimiting system we have proposed.

At 9:40 AM -0800 00.3.31, Paul Bottorff wrote:
> Osamu:
> A major difference between T1X1.5 and 802.3ae is that T1X1.5 is encoding
> over SONET, supporting all SONET clock, jitter, and management
> requirements, while 10 GigE WAN-PHY uses Ethernet compatible timing. This
> makes these two standards very different. It also address the issue of
> having a simple low cost WAN access media (10 GigE) and at the same time
> having a full fledged SONET compliant version.

Osamu Ishida
NTT Network Innovation Laboratories
TEL:+81-468-59-3263 FAX:+81-468-55-1282