[802.3ae_Serial] From Serial PMD 19 June: 850nm eye mask, ORL spec, 1310serial max Tx power, ...
Eye mask for 850 nm
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850 nm proponents, please notice that the serial ad hoc is charged with
producing a proposal for a 850-specific eye mask which would preserve the
transmitter integrity requirements of the current draft standard but remove
the need for rise time specification and measurement. This might be like a
scaled OC-12 or 1GigE mask. Please email and join next week's call if
interested.
ORL
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We understand that ORL is total Optical Return Loss measured by
disconnecting a transmitter from a link and measuring the link with a
reflectometer. The far end receiver remains attached. Historically this
has been a requirement of SONET but not of Ethernet. It seems that it
guards against multiple reflection effects (parasitic etalons) in single
mode links, where reflections that are individually within spec combine to
create a problem.
The following is a table (E&OE):
| G.691 | 10GE |
Discrete | 27 | 27 | 26 | 26 |
Receiver | 14 | 24 | 12 | 26 |
ORL | 14 | 24 | - | - |
RIN test | - | - | 12 | 21 |
If the ORL requirement is there to protect the transmitter from back
reflection, 10G Ethernet could reasonably use the same numbers for ORL spec
as it uses for RIN test. Input from the fibre and cabling community on the
merit of an ORL spec at 1310 and/or 1550 nm is needed: please email or join
next week's call!
Receiver overload
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Suggested re-calculating the Tx max mean power from current likely Tx min.
mean power + 5 dB for tolerances (keeping the 5 dB range we started with).
How is stressed eye ISI value derived?
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Thought to be calculated using a high receiver bandwidth rather than the
usual 7.5 GHz, and with TP3 DCD (6 ps) rather than TP4 (8 ps). If this is
right, to be recorded in "Notes" page of link model at next revision.
Jitter
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0.015 UI sigma_RJ thought to be too small. Obviously too much causes an
error floor, but maybe 0.025 UI would be in the right ball park? But we
don't know what would cause Tx RJ apart from RIN, because most oscillator
phase noise is expected to be <4 MHz and tracked out by Rx PLL.
We have accounted for some DJ in the model with the DCD factor. We are
still thinking in the range 0.3 to 0.35 UI.
Next meeting
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Agenda items to include:
850 nm mask proposals
ORL spec
Receiver overload
Refining jitter DJ and RJ spec numbers
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