Re: What is 802.3ae WAN-PHY?
Hi Roy, Hi Dave,
Thank you for your feedback. Your comments are helpful for me to
understand what was going on in HSSG and T1, since I have joined
HSSG since the Dallas meeting (Jan. 2000) and I have no liaison
to T1.
Before discussing in detail, I think we had better be aware once
again that here is a LAN community, and keep in our mind that we
should be much careful to use WAN terminology. I use the
following definitions in this mail; please let me know if there
is any inconvenience to you.
--------------- --------------- ------------ ----------- ------
expression Overhead access CLK Accuracy CLK Jitter Std.
--------------- --------------- ------------ ----------- ------
SONET (almost) full < +/-20ppm SONET spec. T1.105
SONET-compliant reduced < +/-20ppm SONET spec. T1.416
SONET-lite much reduced < +/-100ppm ?????????? ??????
--------------- --------------- ------------ ----------- ------
Here I assume that SONET-lite equals WAN-PHY with SONET framer
proposed in 802.3ae.
I think we can agree on the following two facts;
(1) There is no SONET-lite standard at present. All SONET or
SONET-compliant equipment at present, including the emerging
non-muxing LTE, should meet +/-20ppm CLK accuracy and SONET
jitter spec.
(2) Pointer manipulation mechanism in SONET framer itself has
the potential to accommodate the CLK difference up to +/-320ppm.
According to Roy, there are some discussions on relaxing the SONET
CLK accuracy for some specific applications in T1 or ITU-T. That's
news to me; please let me know where I can get the more information
about the discussion.
I have no authority to decide how NTT reacts in ITU-T, but I will
strongly recommend my colleagues who often attend the ITU-T expert
meeting not to approve such standard proposals. The reasons are;
(1) I know we have at least one SDH system that raises an alarm for
too many pointer re-writing to indicate wrong CLK accuracy.
(2) It can not be connected to SONET regenerators. This implies
that it is not a SYNCHROUNOUS system any more. I see no reason
to define 'plezioisosynchronous' system with SONET framer which
is optimized for SYNCHRONOUS systems. Note that we have a
serious trade-off between CLK accuracy and jitter transfer in a
SONET regenerator (you can read it in SYNCHRONUS transport systems).
I think this is what Erik has pointed out in his recent comment.
http://grouper.ieee.org/groups/802/3/10G_study/email/msg02157.html
(3) I'm afraid that it would nominate the client path; only OC-192c
or some small variations could be carried through non-muxing LTE.
We will lose flexibility to accommodate any combination of OC-1,3,
12,48,192. Or we require very heavy Line terminating circuit to
re-write up to 192 pointers independently.
Above consideration tells me that, if we use the SONET framing,
we had better keep +/- 20ppm accuracy to be compliant to SONET.
Then it can be connected directly to existing SONET regenerators and
WDM active transponders. We don't need to pay the SONET-framing
charge twice for WAN-PHY and ELTE. And again, I don't believe
SONET regenerator for 10GbE is a good choice unless you have already
invested in it.
http://grouper.ieee.org/groups/802/3/10G_study/email/msg01869.html
Best Regards,
Osamu
At 14:39 00/04/07 -0500, Roy Bynum wrote:
http://grouper.ieee.org/groups/802/3/10G_study/email/msg02169.html
>
> Osamu,
>
> "SONET Lite" is a term that has been used for some time to mean a reduced
> overhead requirement customer drop interface. T1.416-99 defines the
> required and optional byte usage for "SONET Lite". The plezioisosynchronous
> timing standard is currently being worked on. It should be a full standard
> definition very soon. In this regard, the "ELTE" is acutely a special case
> non-muxing LTE that is part of the T1X1 standards. The SONET test sets that
> are used for POS today already have to be adjusted to allow for wider clock
> and jitter tolerance.
>
> Thank you,
> Roy Bynum
>
> ----- Original Message -----
http://grouper.ieee.org/groups/802/3/10G_study/email/msg02164.html
At 15:42 00/04/07 -0400, David W. Martin wrote:
http://grouper.ieee.org/groups/802/3/10G_study/email/msg02170.html
>
> Osamu,
>
> Our WAN PHY proposal uses the traditional +/-100ppm clock tolerance spec
> of Ethernet. An ELTE would have a matching WAN PHY interface. The SONET
> side of the ELTE will have an ITU/ANSI interface. Within the ELTE the clock
> domain adaptation is performed using traditional SONET pointer processing.
> Previous material has shown this is feasible. Please refer to
>
> http://grouper.ieee.org/groups/802/3/10G_study/public/july99/bottorff_1_0799.pdf
>
> for more background. Thank-you.
>
> ...Dave