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Re: Gearbox reality check

Rich, Roy,

It could be the terminology that is confusing the issue. I don't
think the results are any different.

The SONET frame is byte aligned.

The OH content is bytes.

The SPE content is 66-bit words when being filled or emptied
at the WIS. Since the SPE is not an integral number of 66
bits, the last word in 1 SPE will often "spill over" into
the next SPE.

The SPE content is considered bytes when being passed through
the SONET network. When the SONET network needs to "adjust"
1 SPE with respect to another SPE in order to account for
clock jitter and tolerances, it does so on byte boundaries.
This could potentially further separate a 66-bit word. The
SONET network also uses byte boundaries to find the OH bytes
within a frame.

The result is that the WIS is required to parse the SPE based
on byte boundaries as indicated by the pointer logic (to find
the start of the SPE) but the data it extracts is organized as
66-bit words, i.e. it only uses the byte boundaries to find the
start and end of the SPE and to separate the OH bytes, while
the content of the SPE is considered a collection of concatenated
66-bit words.

How close is this?


Rich Taborek wrote:
> Roy,
> This is the one of the tasks performed by the WIS. As I've explained, the SONET
> OH is byte aligned and the data within the SPE is 66-bit aligned. Conversion at
> each end is performed by the WIS.
> Best Regards,
> Rich
> --
> Roy Bynum wrote:
> >
> > Rich,
> >
> > A minor correction to one of your statements.  In spite of the proposal to use a 66 aligned data stream in the WAN compatible PHY,
> > the SPE remains byte aligned.  There has to be some sort of, as yet undefined, "gear box" to stuff, re-time, and re-align the 66 bit
> > data stream into the byte aligned transmission signaling stream payload.
> >
> > Thank You,
> > Roy Bynum
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