RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Hi Rao,
10GBASE-E has:
Table 52-18
Return loss of the receiver (min) 26 dB
Table 52-19 and 52.14.2.2
Return loss for any device in the optical link 26 dB. This is equivalent to
ITU-T's maximum discrete reflectance.
Table 52-26
Optical return loss of the Fiber optic cabling (channel) 21 dB
(editor: this should say "(min)"). This is equivalent to ITU-T's ORL. It
does not have a return loss spec on the transmitter, which 10GBASE-L does
have. 10GBASE-S differs again.
If this is not sufficiently clear, please suggest better wording to the
editors.
Thank you,
Piers
-----Original Message-----
From: Christensen, Benny [mailto:benny.christensen@intel.com]
Sent: 12 February 2002 09:26
To: Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
Subject: FW: [802.3ae_Serial] 12 dB return loss for transmitter?
-----Original Message-----
From: Christensen, Benny
Sent: 12. februar 2002 10:25
To: 'Rao Tatavarti'
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Hi Rao
You are quite right about this. But that specification is related to the
optical fiber link installed, not the PMD of the 10GE port.
Brillouin backscattering is mainly a problem with high launch power (in
excess of 10 dBm, ie. when one uses EDFA with up to 30 dBm lauch power). It
depends very much on the optical spectrum power density (which can be
broadened by chirp of the laser/modulator or low frequency laser current
modulation - spreading the spectrum. This technique is coverd by a patent
(BT as far as I remember).
Rayleigh backscattering is always present an has some effective length of
around 20 km and a level of around -60 dB (as recalled from my mind). This
is normally not a problem and far less than discrete reflections in the
fiber (connectors and splices)
Benny
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GIGA, an Intel company
Benny Christensen, M.Sc.E.E, Ph.D.
Mileparken 22, DK-2740 Skovlunde, Denmark
Tel: +45 7010 1062, Fax: +45 7010 1063
e-mail: benny.christensen@intel.com, http://www.giga.dk
-----Original Message-----
From: Rao Tatavarti [mailto:rao@ceyba.com]
Sent: 12. februar 2002 00:53
To: Christensen, Benny; Ron Miller; Lindsay, Tom; Serial reflector 802.3ae
(E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Hi all,
Optical Return Loss (ORL) according to ITU is a optical spec specified at
the Transmitter. This denotes the returned power from the entire fibre
including both discrete reflections and distributed backscattering such as
Brillouin or Rayleigh scattering.
ITU has no specifications for target link distances of 10km as in 10GE
spec. The closest is the I-64.2 or the SR-1 in GR253 which has a value of
14dB.
Another specification that is specified along with ORL is a max discrete
reflectance specification for the optical path between S and R, which in the
ITU case is -27dB max. I am not aware of 10GE equivalent spec for this
parameter.
Rao Tatavarti. Ph.D
Ceyba Inc.,
450 March Road,
Kanata, Ontario K2K 3K2
Email: rao@ceyba.com
Tel: 613 599-5797 ext 5083
Fax: 613 599-1247
-----Original Message-----
From: Christensen, Benny [mailto:benny.christensen@intel.com]
Sent: Friday, February 08, 2002 3:33 AM
To: 'Ron Miller'; 'Lindsay, Tom'; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Hi all
My perception is, that this is an optical specification and as such it is
the optical return loss (measured from the fiber side).
Just like SDH/SONET specifications, 10GE is an interface specification (at
optical connections points S (=TP2) and R (=TP3)), and (optical) properties
of the TX (jitter, rise/fall, eye mask etc.) and RX (sensitivity, tolerance
etc.), ie. things that can be measured from the outside of the modules.
All 3 standards does not cover internal components specifications like the
optical modulators S11 (electrical return loss) nor the MUX (driver)
rise/fall time, output swing or S22. These things are 'implementation
specific' and as such it is unimportant, as long as the functionality and
specifications are fulfilled at point S and R.
From a module vendors point of view, it will of course be nice to have some
standard definitions for the interfaces at a component level, but I think it
is out of scope for the 10GE standard.
XSBI/OIF/MSA interface (where instantiated) are covered in the same way.
Benny
--------------------------------------------
llllllll ii llllllll llllll
ll ll ll ll
ll llll ll ll llll llllllllll
ll ll ll ll ll ll ll
llllllll ll llllllll ll ll
GIGA, an Intel company
Benny Christensen, M.Sc.E.E, Ph.D.
Mileparken 22, DK-2740 Skovlunde, Denmark
Tel: +45 7010 1062, Fax: +45 7010 1063
e-mail: benny.christensen@intel.com, http://www.giga.dk
-----Original Message-----
From: Ron Miller [mailto:rmiller@brocade.com]
Sent: 8. februar 2002 06:44
To: 'Lindsay, Tom'; Ron Miller; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Hi Tom
I believe that this is the electrical connection to the electro/optical
module.
In the case of the optical transmitter(optical output) the same logic is
appropriate. However,
it is typically possible to get 30 or more db return loss. also in the
optical arena the source laser
can often be pulled in frequency by the reflected wave from the load, which
may be a more important
source of degradation than the third pass signal combining with the incident
signal at the receiver end.
Insertion loss S21 is from input to output. Return loss is reflected power
and at the sending end is usually
referred to as S11, and at the receiving end S22. All parameters are
complex numbers.
Good luck
Ron
-----Original Message-----
From: Lindsay, Tom [mailto:tlindsay@stratoslightwave.com]
Sent: Thursday, February 07, 2002 4:04 PM
To: Ron Miller; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Does everyone agree with Ron?
Ron, do you understand that this is an optical spec?
Thanks, Tom
-----Original Message-----
From: Ron Miller [mailto:rmiller@brocade.com]
Sent: Tuesday, February 05, 2002 10:40 PM
To: Lindsay, Tom; Serial reflector 802.3ae (E-mail)
Subject: RE: [802.3ae_Serial] 12 dB return loss for transmitter?
Tom
This is the return loss looking back into the transmitter. Typically it is
measured with the
drive circuit powered. It is an AC measurement, and may vary according to
the signal that
the transmitter is sending out.
The value of this measurement is in calculating or simulating the third pass
signal, which is the
combination of the driving signal together with the reflection from the
destination, coming back to the
source and reflecting again. The total reflection from the source
termination and the load termination
should be at least 20 db total for +/-10 percent ripple in the rails of the
eye pattern. So, 12 db at
each end would be 24 db or about +/ -6 percent ripple. So, you normally
want to do better. 20 db is
a very safe number at both ends resulting in 40 db or only about +/-1%
ripple in the rails.
Ron miller
-----Original Message-----
From: Lindsay, Tom [mailto:tlindsay@stratoslightwave.com]
Sent: Tuesday, February 05, 2002 9:24 PM
To: Serial reflector 802.3ae (E-mail)
Subject: [802.3ae_Serial] 12 dB return loss for transmitter?
Dave Kabal, Dubravko and I were discussing the 12 dB return loss spec in
Table 52-12.
What is it? Is this return loss looking back into the transmitter port from
outside, or is it tolerance to return loss of the cable plant and receiver
combination?
If the former, what is the technical reasoning? If the latter, it should at
least be renamed or more preferably removed.
Thanks, Tom
Stratos NW
425/672-8035 x105