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RE: Connector Return Loss

Good point on passive splitter systems. Similar concerns exist for
bi-directional transmission on the same fiber at the same wavelength. For
EFM, both of these systems will probably be only on singlemode fiber and use
singlemode connectors. While outside the scope of Structured Cabling
Standards, the improved return loss performance that may be required for SM
connectors is found elsewhere. For example, Telcordia now requires at least
40 dB return loss for singlemode connectors. Fortunately, products exist
that easily meet this performance level. 

	From:  Geoff Thompson [SMTP:gthompso@xxxxxxxxxxxxxxxxxx]
	Sent:  Wednesday, April 11, 2001 6:22 PM
	To:  Kolesar, Paul F (Paul)
	Cc:  802.3ae; 'Doug.Coleman@xxxxxxxxxxx'
	Subject:  RE: Connector Return Loss


	The only thing that I would add is that there is a 25 dB return loss

	requirement for MM in 10BASE-F ( for 10BASE-FP (Passive
Star). As 
	we start to consider both passive splitter systems and single fiber
	in EFM return loss may again rear its ugly head.


	At 11:02 AM 4/11/01 -0400, Kolesar, Paul F (Paul) wrote:

	>Here are my views:
	>The 20 dB level for MM connectors is historical in that that has
been the
	>spec used by previous generations of application standards and is
	>agreement with cabling standards.
	>The 26 dB level for SM connectors initiated in Fibre Channel in the
early to
	>mid nineties. I believe this was at the request of 1300 nm
	>vendors. It is also in agreement with cabling standards. It is
	>to not that Telcordia (formerly Bellcore) used 27 dB in the past,
which I
	>believe was in concert with SONET equipment standards.
	>The use of isolators in the transceiver is a design choice and not
	>by IEEE 802.3. The receiver is specified with a minimum return loss
	>the value of which has been the subject of debate.
	>What type of testing are you referring to? Transceiver or cabling?
	>Paul Kolesar
	>Lucent Technologies
	>         ----------
	>         From:  Doug.Coleman@xxxxxxxxxxx
	>         Sent:  Wednesday, April 11, 2001 9:23 AM
	>         To:  802.3ae
	>         Subject:  Connector Return Loss
	>         Does anyone know the history behind the connector return
	>         proposed for 10 GbE?
	>         The return loss for multimode connections shall be greater
than 20
	>         The return loss for single mode connections shall be
greater than 26
	>         Do the transceivers integrate isolators into them to
address return
	>         Has any testing be done to demonstrate compatibility?
	>         Thanks
	>         Doug Coleman
	>         Corning Cable Systems