Re: [8023-10GEPON] FW: Bridge details
Frank and all,
I would add that this approach requires reading between 66 and 131 bits
(assuming that number of errors does not exceed the threshold, otherwise we
would continue reading). Of course, it can also be further optimized s.t.
once we found 55 matching bits, we may stop, since the remaining bits, even
if all mismatched, are below the error threshold.
I think Daido-san's question was about my initial proposal to lock on block
boundary first, and then do block-by-block comparison to find the delimiter.
To lock on block boundary, we use the same technique that Frank described.
Read bit stream and compare to known sync pattern. Sync pattern is selected
such that at every shift position, except the matching position, it has at
least 30 bits different (take a give few for possible errors). Once we found
a position with small number of mismatches (say, less then 15), we declare
lock. This is a very robust scheme, as it tolerates a large number of
errors per block.
Once we locked on block boundary (stage 1), continue comparison block by
block (without bit shifting), looking for the delimiter value (stage 2).
Glen
> -----Original Message-----
> From: EffenbergerFrank 73695 [mailto:feffenberger@HUAWEI.COM]
> Sent: Thursday, December 14, 2006 10:22 PM
> To: STDS-802-3-10GEPON@listserv.ieee.org
> Subject: Re: [8023-10GEPON] FW: Bridge details
>
> Dear all,
> On the number of correlators needed to do a 66 bit correlation...
> I can answer this question like this:
> If the correlator operates serially, then you need 1 correlator.
> That is, if this correlator circuit checks each bit alignment in one bit
> time, that you need only one.
>
> If the correlator is working with a 16 bit wide data bus, then you need 16
> correlator circuits.
>
> What's involved in a correlator circuit, you might ask? Fundamentally, 66
> XOR gates, plus some adding logic to count the bits that don't match.
> This is somewhat simplified in that once the count goes over 11 bits, we
> don't care (12 or more mismatching bits is declared a non-lock). I can't
> imagine that this goes over 200 hundred gates.
>
> Sincerely,
> Frank Effenberger
>
>
> > From: Fumio Daido [daido-fumio@sei.co.jp]
> > Sent: Thursday, December 14, 2006 12:11 PM
> > To: glen.kramer@teknovus.com
> > Cc: 'Frank Effenberger'; Jeff Mandin; kj-tanaka@kddilabs.jp;
> > marek.hajduczenia@siemens.com; 'Ryan Hirth'; 'Frank Chang';
> > piers.dawe@AVAGOTECH.COM; 'Shoichiro Seno'; k-shiraishi@bq.jp.nec.com
> > Subject: Re: Bridge details
> >
> > Glen,
> >
> > I reviewed proposals after FEC adhoc tel conference. I will show
> > you my concern as follows.
> >
> > Could you estimate how many 66 bits correlator to detect 66B
> > boundary are needed for instant lock of 66B block? I think pararel
> > implementaion is needed for quick lock. I am concerned about size
> > of hardware for detecting 66B block boundary.
> > If 64 bits delimiter (exclude 2bit sync bits) is large, 64 bits
> > delimeter can be divided into 32 or 16 bits delimeter.
> >
> > Regards,
> > Fumio Daido
> >
> >