+---------------------------+
                        |  Fiber Optic Loss Budget  |
                        +---------------------------+



    The following  figures  represent  the  calculated loss budget for
    fiber optic segments used to interconnect the following devices:

         DECRepeater 90FA  (DEFAR)
         DECRepeater 90FL  (DEFMR)
         DECBridge   90FL  (DEWGF)
         DECrepeater 90FS  (DEFMI)
         DECrepeater 900FP (DEFMM)

    These figures account  for  the  connectors  at  either end of the
    segment.  Furthermore, these  figures  are  calculated  using  the
    transmit and receive optical power  levels of the above equipment.
    When connecting to or from different  devices,  the  transmit  and
    receive optical power levels of the other  devices  must  be taken
    into account.



    10-Base FL Worst-case Loss Budget (0 to 50 degrees C, end of life) 
    ------------------------------------------------------------------

Multimode, Graded 
Index Fiber Size      (um)   50/125  50/125  50/125  62.5/125  85/125  100/140

Numerical Aperture 
(NA)                   -      0.20    0.21    0.22    0.275     0.26    0.30

Minimum Average 
Transmit Power        (dBm)  -22.8   -23.3   -22.9   -19.0     -16.8   -13.5

Minimum Average 
Receive Sensitivity   (dBm)  -32.5   -32.5   -32.5   -32.5     -32.5   -32.5

10-BaseFL Loss Budget
(Pt,avg - Pr,avg)     (dB)     9.7     9.2     9.6    13.5      15.7    19.0



                         FOIRL Compatibility
                         -------------------

    The older 802.3 FOIRL standard specified a -27.0  dBm minimum PEAK
    receive power (Pr, avg = -30.0 dBm).  This  power level represents
    a  2.5 dB lower receiver sensitivity.  The worst-case loss  budget
    for FOIRL  compatibility  purposes should include this decrease in
    receiver sensitivity and is given below.





     FOIRL Worst-case Loss Budget (0 to 50 degrees C, End of Life)
     -------------------------------------------------------------

Multimode, Graded 
Index Fiber Size      (um)   50/125  50/125  50/125  62.5/125  85/125  100/140

Numerical Aperture 
(NA)                   -      0.20    0.21    0.22    0.275     0.26    0.30

Minimum Peak
Transmit Power       (dBm)   -19.8   -20.3   -19.9   -16.0    -13.8   -10.5

Minimum Peak 
Received Power       (dBm)   -27.0   -27.0   -27.0   -27.0    -27.0   -27.0

FOIRL Loss Budget    (dB)      7.2     6.7     7.1     11.0    13.2    16.5


    The older 802.3  FOIRL  standard specified a maximum -9.0 dBm PEAK
    receive power, Pr,peak (Max  Pr,avg  = -12 dBm), and a maximum -10
    dBm  PEAK launch power, Pt,peak  (Max  Pt,avg  =  -13dBm).    When
    calculating the loss budget for FOIRL  devices,  a concern is that
    the higher output from the DEFAR, DEFMR, and DEWGF, in conjunction
    with the increased launch power into the two  largest  fiber sizes
    (85/125,  and  100/140),  does not overload FOIRL receivers.   The
    worst  case numbers for FOIRL devices should therefore include the
    maximum launch power figures, which are given below.



     Best Case Maximum (Peak) Launch Power (0 to 50 deg. C, )
     --------------------------------------------------------

Multimode, Graded 
Index Fiber Size      (um)   50/125  50/125  50/125  62.5/125  85/125  100/140

Numerical Aperture 
(NA)                   -      0.20    0.21    0.22    0.275     0.26    0.30

Maximum Peak
Transmit Power       (dBm)   -12.8   -13.3   -12.9    -9.0     -6.8*   -3.5*



*  Additional attenuation is required when connecting the above devices via 
   short lengths of 85/125 micron and 100/140 micron fiber optic cable.