Cisco 7000 Series Hardware Installation And Maintenance Manual page 71

multimode transmissions assumes minimum transmitter power (PT), maximum link loss (LL), and
minimum receiver sensitivity (PR). The worst case analysis provides a margin of error, although not
all of the parts of an actual system will operate at the worst case levels.
The power budget (PB) is the maximum possible amount of power transmitted. The following
equation lists the calculation of the power budget:
PB = PT – PR
PB = –18.5 dBm – (–30 dBm)
PB = 11.5 dB
The power margin calculation is derived from the power budget and subtracts the link loss, as
follows:
PM = PB – LL
If the power margin is positive, as a rule, the link will work.
Table 2-10 lists the factors that contribute to link loss and the estimate of the link loss value
attributable to those factors.
Table 2-10 Estimating Link Loss
Link Loss Factor
Higher order mode losses
Clock recovery module
Modal and chromatic dispersion Dependent on fiber and wavelength used
Connector
Splice
Fiber attenuation
After calculating the power budget minus the data link loss, the result should be greater than zero.
Results less than zero may have insufficient power to operate the receiver.
For SONET versions of the AIP module, the signal must meet the worst case parameters listed
in Table 2-11.
Table 2-11 AIP Minimum SONET Signal Requirements
Single-Mode Multimode
PT –18.5 –15
PR –30 –28
PB –11.5 –13
Estimate of Link Loss Value
0.5 dB
1 dB
0.5 dB
0.5 dB
1 dB/km
Site Requirements
Preparing for Installation 2-11