name	speed	wavelngth	mode	XMIT Max (dBm)	XMIT Min (dBm)	Rcvr sensitivity (dBm)	Loss Budget (dB)	Dist Limit	Optics pair cost
10 FL	10 Mb/s	850 nm	mm	-12	-20	-32.5	12.5	2000 M
100 FX	100 Mb/s	1300 nm	mm	-14	-20	-31	11	2000 M
1000 SX	1 Gb/s	815 nm	mm	-3.2	-9.5	-17	7.5	220 M	$1,000
1000 LX	1 Gb/s	1310 nm	mm	-9	-11.5	-19	7.5	550 M **	$2,000
1000 LX	1 Gb/s	1310 nm	sm	-9	-11	-19	8.0	5 KM	$2,000
1000 ZX	1 Gb/s	1550 nm	sm	5.2	0.0	-24	8 to 24	70 KM	$12,000

mm = multimode ; these numbers are for FDDI grade 62.5 micron fiber core

sm = singlemode ; 9 micron fiber core

optics costs are Cisco full list price for a pair of GBICs

ZX has a minimum loss requirement to avoid saturating the receiver. Other types will not saturate even with short low loss jumper cables.

10 and 100 Mb/s use diode emitters; 1 Gb/s uses class I laser emitters

** A special mode conditioning cable is required to achieve more than 200 meters with multimode fiber.

Emerging standards for 10 G/s LAN fiber interconnect.

name	speed	wavelength	mode	Dist Limit
10GbaseLR	10 Gb/s	1310 nm	sm	10 KM
10GbaseER	10 Gb/s	1550 nm	sm	40 KM
10GbaseSR	10 Gb/s	850 nm	mm **	65 M
10GbaseLX4	10 Gb/s	1310 nm WDM	mm **	300 M

** The multimode fiber contemplated here is "laser enhanced" 50 micron core diameter. 65 meters may be a soft limit depending on the detailed bandwidth specification of the fiber. LX4 encodes the data over four separate wavelengths.

dBm is a measure of power, like watts.  
         0 dBm = 0.001  Watt
        10 dBm = 0.010  Watt
       -10 dBm = 0.0001 Watt

Loss budget = Min_Transmit_Power - Rcvr_Sensitivity

If you attach a power meter with a 62.5 micron jumper to one of the mm
sources above, you expect to see a power level between Min and Max.

Rcvr sensitivity means with at least this much power delivered
to the receiver the design error rate can be achieved. 1:1,000,000,000

At 10 and 100 Mb/s, the distance limit for full duplex systems is due
to loss of light.  At 1 Gb/s over multimode fiber, the limit is due
to fiber bandwidth.

If too much power is delivered to the receiver it is possible to
overload it.  With long range ZX optics, if the fiber link provides
less than 8 dB of loss, additional attenuation should be added.

It is technically permissible to use LX for short range fiber applications
because the fiber path is not required to have attenuation to prevent
overload.

Rules of thumb 

   At Gig speeds, most of our light losses come from the connectors 
   and only a very small amount from the fiber.

   The faster we go, the lower the loss budget we get to work with.
   The more important it is to treat connectors with great respect and
   minimize patch cables.  Using ZX to make up for connector losses is 
   a very expensive proposition.

   Over its useful life, an ordinary light bulb loses about half its
   brightness before it burns out.  The same is true for fiber optic
   light sources.  The loss budget numbers allow for expected lower
   output over the useful life of the fiber transceiver.  The aging
   process "settles down" after a few thousand hours.  Fiber light
   sources don't have a "burn out" mechanism that is similar to light
   bulb filaments.

Version of Dec 15, 2002