PRBS23 test pattern -- RE: [802.3ae]802.3ae PRBSs are upside down
I agree that the PRBS23 uses "inverted data". I think
O.150 is clear on this.
I also maintain that the PRBS23 output should be taken from the
MSB of the register, as implied in O.150 section 4. In section 4
it refers to the "output of the shift register" as opposed
to the input to the shift register (which we are using as the output
in the optional PRBS31).
The payload data will differ between implementations since
we reset the prbs every frame. If a vendor wants to build in
the pattern, and we are not concise about where in the shift register the
output is located, and whether it is inverted,
they better build in both sequence starting
points, and both polarities with respect to the CID.
> -----Original Message-----
> From: Tim Warland [mailto:twarland@xxxxxxxxxxxxxxxxxx]
> Sent: Wednesday, March 06, 2002 10:53 AM
> To: Nepple, Bruce
> Cc: ieee
> Subject: Re: [802.3ae]802.3ae PRBSs are upside down
> "Nepple, Bruce" wrote:
> > <snip>
> > My issue is that when you apply this to the PRBS23 (which
> is reset every frame),
> > you end up with incompatible payloads in WIS test mode.
> This means that if
> > test equipment vendors build in patterns (not required by
> the specification),
> > they need to have all the combinations of inverted and
> delayed available.
> > Seems unnecessary. It's not really important how it is
> done, just so it
> > is specified consistantly and everyone does it the same way.
> The PRBS in the WIS test pattern is separate from the PRBS31
> we are discussing
> for both clause 49 and 50.
> The WIS test pattern was designed specifically for bit based
> BERT testers. This
> test pattern will not work in any other kind of tester
> because the payload PRBS
> is reset and truncated every frame. The PRBS23 is specified
> in accordance
> O.172 (Annex A.2) which references O.150 for the PRBS23 pattern.
> From O.150, the PRBS23 has the inverter for (what we call)
> the normal frame, and
> does not have the inverter for (what we call) the inverted
> frame. In retrospect, I
> see that there is no real advantage in inverting the entire
> SPE, only inverting
> the CID would have been sufficient. It's one of those things
> where there is no
> compelling argument to change it.
> Is that the answer you were looking for?
> Tim Warland P. Eng.
> Applications Engineer
> Quake Technologies (613)270-8113 ext 2311
> Tough Times don't last, tough people do