AW: [802.3ae_Serial] Tx setup window with OMA
Hi,
this illustrates where we end with this OMA spec. A lot of the values
indicated present severe issues on Receiver designs and are not available in
state of the art devices. In contrast to this a set of parameters is
specified that can hardly be controlled in designs in control loops and so
on, so the designs will always support kind of average value control loops.
There is a very wide tolerance range on the transmitter side (presenting
severe problems at receivers) however now is stated that it is not wide
enough. This due to the fact that in respect to some parameters the ranges
are widened up to values which will likely never be present in real systems.
So for instance in the 1550 case ultra high ERs are irrelevant as this will
fail in respect of chirp anyway if not a MZ is used so the spec for only
amplitude does not have any value. Direct modulated sources which think have
bee the reason for the very low minimum ER, are orders of magnitude away
from required chirp so are not realistic today while the RMS width
calculation gives the impression that this might be possible. As ITU experts
stated (Who as I understood discussed and studied this in detail in the
past/ this was long before my standards participation time) this is an
incorrect model for this purpose, neglecting the main influence. This means
the spec is based on technologies that are only future options and not
available at some places and present severe stress on other parts.
It should be noted if such power values are used in 1550 than we do not have
any useful piece of equipment today. (1310nm is not much different.)
Regards Juergen Rahnn Rahn
> ----------
> Von: DAWE,PIERS (A-England,ex1)[SMTP:piers_dawe@xxxxxxxxxxx]
> Gesendet: Montag, 30. Juli 2001 20:11
> An: '802.3ae Serial'
> Betreff: [802.3ae_Serial] Tx setup window with OMA
>
> <<Datei: Pave_OMA_LX.pdf>><<Datei: Pave_OMA_LRW.pdf>>
> As I wrote two days ago, the setup window for the LR/LW, 1310 nm serial,
> PMD, at low extinction ratio is 4 dB when 5 dB was intended.
>
> For the ER/EW, 1550 nm serial, PMD, the window is around 3.5 dB if TPD
> (transmitter and dispersion penalty) is small and extinction ratio is its
> minimum 3 dB, or 0.4 dB (!) at maximum TPD, minimum extinction ratio.
>
> For the SR/SW, 850 nm serial, PMD, the window at 3 dB extinction ratio is
> very roughly 2 dB; it depends strongly on the triple trade off.
>
> The attachment Pave_OMA_LX.pdf is an example of an old style (mean power
> based) standard that works: the 1 Gigabit Ethernet LX standard. The setup
> window is 8 dB wide. Because both the upper and lower limits are measured
> on the same basis, the window is 8 dB wide for any extinction ratio. (P1
> means the power in the ones.)
>
> At 10 Gbit/s we don't want to set a very high receiver overload value, we
> want to enable lower extinction ratios, and to enable cost-effective
> transmitters we wish to specify them on an OMA basis. The attachment
> Pave_OMA_LRW.pdf shows where the LR/LW, 1310 nm serial, PMD is at in draft
> 3.1. The setup window is 4 dB wide at 4 dB extinction ratio.
>
> How can we fix this?
>
> Options are:
> 1. Reduce the Tx OMA spec. Would need better receivers and/or reduced
> link attenuation. Not attractive.
> 2. Raise the Tx mean power spec back to 1 dBm. This works.
> 3. Specify the Tx maximum power on a maximum-in-in-the-ones basis at
> e.g. +3 dBm. This seems to work too. It's a reasonable compromise
> between
> the transmitter's primary metric (OMA) and the receiver's overload concern
> (power in the ones? mean power? OMA? it may depend on receiver
> implementation).
> 4. Specify Tx maximum in OMA, at say +1 dBm. This makes the setup
> window independent of extinction ratio again but it gives the receiver a
> hard time.
> 5. A combination of 2 and 3 above, as illustrated in purple. Not sure
> that the benefit over the better of options 2, 3 outweighs the cost of the
> extra test involved.
>
> Option 2 isn't an original idea. It was proposed for 1550 nm in
> http://www.ieee802.org/3/ae/public/jan01/frojdh_2_0101.pdf and shelved
> because it wasn't essential to fix anything broken and we wanted to know
> more about how 1550 nm receivers overload before taking it up.
>
> Piers
>
>