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# RE: Maximum run length of 64/66b

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Mike and Shen,

Sorry I didn't get to answering sooner. I was busy getting
clause 49 ready for D2.0 and other tasks.

The maximum run length is 66 which can occur when a data frame is
followed by a control frame or vice versa. There is always a transition
between the two bits of the sync header. The probability of a run of
65 or 66 bits is 2^64 ~ 16 * 10^18.

One can AC couple just as one can with any scrambled code. On the average
about half the bits will be zero and half will be one. The cut-off frequency
will be much lower than for something like an 8B/10B code, but it does not
have to go down to zero.

Regards,
Pat

-----Original Message-----
From: Mike Jenkins [mailto:jenkins@xxxxxxxx]
Sent: Tuesday, November 14, 2000 2:45 PM
To: stds-802-3-hssg@xxxxxxxx
Subject: Re: Maximum run length of 64/66b

Hello,

Perhaps I missed it, but I haven't seen any responses to the
question below, so let me hazard a guess and hope that someone
corrects me if I'm wrong:

1) The max run length is 66, since the sync bits are not
scrambled.

2) I suspect the frequency content is sufficiently low that
any AC coupling would be impossible.

Improved theoretical or empirical results might help 64b/66b
serve other applications as well as this one, I would think.
Opinions anyone?

Regards,
Mike

ss_shen@xxxxxxxxxxxxxxxxx wrote:
>
> Hi :
>
> This maybe a silly question, but if someone can
> tell me, would be much appreciated.
>
>  (1)  the Maximum run length of 64/66b:
>       Before scramble, the worse run length is
>       65 when it has 01111...... (one "0", 65 "1").
>       What would be the maximum run length after
>       scramble?
>
>   (2) DC balancing aspect of 64b/66b + scramble
>
>  thanks in advance.
>  Best Regards
>  steven Shen
>  Silicon Bridge

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