Re: [8023-10GEPON] FEC, and the need to scramble parity bytes.
Frank,
Would scrambling the FEC parity bytes have any potential detrimental
effect? I ask this because sometimes its is easier to do something
rather than to not do it in some special case (although in this case I
don't think it is a big difference).
Thanks
Duane
Frank Effenberger wrote:
> Dear All,
>
> At the meeting today, there was a small issue on the need to scramble the
> parity bytes that a FEC algorithm produces. As a reference point, I looked
> at G.975, which defines the use of RS(239,255) in SDH systems. It seems
> that this standard suggests that scrambling the FEC output is not necessary.
> (section 6.4.3, first paragraph).
>
> There are two complications that I'd like to point out in fairness.
> 1. G.975 operates by interleaving n encoders (e.g., n=16), so the parity is
> not transmitted in quite the way that we would do. However, the parity is
> transmitted all in a big bunch at the end of the interleaved block, so if
> the parity had some kind of pathological pattern, it would be revealed in
> these systems.
> 2. Section 6.4.3 mentions that in some systems, the main SDH scrambler may
> be disabled, and then in that case a FEC layer scrambler is defined. But,
> that is really a matter of implementation choice, and I don't believe it
> contradicts the main idea that parity that is calculated on scrambled data
> is effectively also scrambled.
>
> So, I would say that we do not need to worry about scrambling the parity.
>
> Sincerely,
> Frank E.
>
>