OMA Rec spec and verification of interface
> Hi,
> The issue in the subject I brought forward at the last meeting is not
> resolved in my view. In the current Draft the Transmitter as well as the
> receiver is specified in OMA. This is done in order to allow bigger
> variance in the transmitter signal in terms of ER and power variation.
> This, in this case leads to the following situation for e.g. the 1300nm
> interface:
> Transmitter power may be vary from: - 6. 22 dBm (coming from calculation)
> in case of very high ER
> to +1dBm as value for the 4 dB ER (in contras to former 3 dB we now have
> complete match).
> This means under an assumption of a compliant path of maximum attenuation
> we can measure either :
> - 13 dBm for high ER signals or up to -6 dBm as max power low ER signal (I
> leave the decimals as this is not suited for verification anyway)
> In case of lowest attenuation, the power may vary between the -6 dBm for
> the high ER signals and +1 dBm for the 4 dB ER signal. This means that
> receive power levels measured with a power- meter do not at all help to
> determine if a receiver power is in spec or not as there is absolutely no
> overlap between the two cases. All the power levels between it cannot be
> verified with a simple power meter as at all power levels between 6 and
> -13 dBm the power may either be correct or too low as function of the ER.
> In such cases the OMA has to be measured at the receiver. This however has
> to be done with an oscilloscope and has further reduced precision in
> comparison to a power meter.
> This means: The verification of the correct receiver power level requires
> specific measurement equipment for verifying the optical amplitude on the
> normal Eye or some means have to be in place to switch the transmitter
> into Test pattern mode (Where I have the question what a test that has
> nothing to do with a normal pattern tells a about the real ER). All this
> is not simple and special complicated measurement means are contradicting
> the idea of a simple interface for compatibility between different
> vendors. This by the way was the reason for specifying the ITU interfaces
> the way this is done, as complicated validation is a direct interface cost
> driver.
>
> The validation of the 1550 nm interface is principally suffering from
> this effect also however if taken the values of the previous draft an
> overlap is present where you can judge that the power is correct in any
> case due to the smaller allowed variation (+4 to ~-1.5 dBm). Under this
> condition the optional attenuators (looking at the values of the former
> draft could solve the problem and make verification of the receiver side
> of the path possible by easy means. (By the way here I have some
> difficulties with the power levels as
> (Here I want to note that there are changes in the draft I do not
> understand as the dB value in the line of minimum OMA is kept but the
> description that these are the dBm of OMA/2 has gone. It this a mistake or
> intentionally?
>
> The situation described is however further complicated due to the fact the
> minimum power (or OMA) is also a function of the dispersion penalty,
> (formerly only for 850nm and 1310nm but also now for the 1550 range). This
> means to verify if the power of an interface is correct you have to
> measure the wavelength and spectral characteristic, which requires
> definitely more that simple low cost equipment. In case of the chirp for a
> 1550nm interface I see the only real chance to use a reference fiber as
> the chirp factor is not specified (which I would not criticizes as the
> behavior and dependencies of the dynamic chirp is really difficult to be
> specified easily). Any way the result is the same, a reference fiber or a
> measurement set for time resolved spectral measurement is contradicting
> the verification of a low cost mass deployed interface.
>
> This may be sufficient to start the discussion on the issues I see on the
> short hand.
> In this context I got a couple of questions in relation to the new draft
> not understanding the we (doubling) and content of the tables.
> I have the assumption that simply some change-marks and strikeouts are
> missing bout do not know if this is true.
> Regards Juergen Rahn
>
>
>
>
>
>
>
>
>
> ----------
> Von: DAWE,PIERS (A-England,ex1)[SMTP:piers_dawe@xxxxxxxxxxx]
> Gesendet: Montag, 9. April 2001 17:06
> An: '802.3ae Serial'
> Betreff: From serial PMD call, 3 April
>
>
> We built a new open issue list; in no particular order:
>
> Trade off jitter and risetime
> -----------------------------
> Proposal to rely more on eye mask, allowing trade off between risetime and
> deterministic jitter. This would simplify testing at 1310 serial and
> maybe
> 1550 serial, avoiding an unsatisfactory rise time test involving four
> histograms. It may allow a good old fashioned performance improvement at
> 1550 where faster rise times can be associated with greater dispersion
> penalty. There may be technical issues between this and the
> wavelength/spectral width/power trade-off, and a highly multi-dimensional
> trade-off would become unmanageable.
>
> Specification of optical transmitter spectral width
> ---------------------------------------------------
> Relation between full width, -20 dB criterion and link model.
>
> Double counting of receiver eye opening penalty
> -----------------------------------------------
> Spreadsheet allows an unretimed receiver sensitivity and then an eye
> opening
> penalty (~0.4 dB). Measured sensitivity of a retimed receiver would
> include
> its own eye opening penalty. Need to at least note the issue in the
> standard.
>
> Other issues raised by the shift to a box level spec
> ----------------------------------------------------
> Perhaps without noticing it, we have moved from a component level standard
> (Gigabit Ethernet) to a box level standard (10 Gigabit Ethernet). We need
> to check that we have made the transition correctly. One known issue is
> that of some components which try to appropriate the whole box's allowance
> to themselves (e.g. jitter).
>
> Interworking between 1310 and 1550 equipment
> --------------------------------------------
> It may be that some 1310 and 1550 equipment could interwork, within
> certain
> loss and dispersion parameters, "by coincidence". Should this get
> mentioned
> or encouraged in the standard? Does it have "broad market potential"?
>
> Bit ordering in clause 51
> -------------------------
> Alignment with SFI-4 vs. Ethernet customs (see reflector traffic). Needs
> joint session of clauses 51, 52. Also involves clauses 49, 50.
>
> Meaning of signal detect
> ------------------------
> Needs joint session of clauses 51, 52 and more.
>
> Measurement filter for RIN
> --------------------------
> Serial ad hoc to find if the filter for RIN should/must be the G.691 (7.5
> GHz) one, i.e. what is built into test equipment?
>
> Delay through PMA/PMD/medium
> ----------------------------
> This delay maximum is defined in clause 44. We need to discuss it in the
> PMD tracks and add
> cross-references in clauses 51, 52 and 54.
>
> Ordering of text in new jitter section
> --------------------------------------
> Other tests have test method and required values in separate sections:
> shouldn't this one too?
>
> Do we prefer dB(OMA) or dB(OMA/2)?
> ----------------------------------
> Argument for dB(OMA): More straightforward relation between OMA
> and dB(OMA)
> Argument for dB(OMA/2): Allows traditional thinking with dB(OMA/2) ~
> "optical power"
> We just need to take a poll on this: there weren't enough people on the
> call
> this week.
> (My own view is that if Fibre Channel had said "Modulated Optical Power =
> (P(1)-P(0))/2" then we wouldn't be having any discussion.)
>
> Topics that don't need to be in weekly call
> -------------------------------------------
> Adding interferometric noise to link model
> Updating link model to reflect [what change?] at 1550 nm
> Possible effect of sinusoidal jitter on link model
> Test patterns - separate call for these
>
> NEXT MEETING
> ------------
> Agenda
> ------
> I thought we might put on the agenda some items which don't need so much
> research:
> Delay maximum
> RIN measurement filter
> Interworking 1310 <>1550
> Other ramifications of shift to a box level spec?
> Transmitter spectral width
> What values of RMS width and full width, -20 dB down, are
> anticipated? What dispersion penalties are anticipated in the 1310 band?
> Any other issues to add?
>
> Time and place
> --------------
> At the usual phone number and new usual time:
> 15:15 GMT = 4:15 pm BST = 8:15 am PDT, Tuesday 10 April 2001, for an
> hour and a half -ish, to finish by 17:00 GMT
> +1(816)650-0631 Access code 39209
>
> People are having difficulty attaching to these calls; apparently the
> issue
> is congestion not number of ports, so persistence is required. I shall
> try
> to open the call five minutes before time to give people a better chance.
>
> Piers
>
>
>