Cisco CX-AIP-TM Installation And Configuration Manual page 9

Attenuation is significantly lower for optical fiber than for other media. For multimode transmission,
chromatic and modal dispersion reduce the available power of the system by the combined
dispersion penalty (dB). The power lost over the data link is the sum of the component, dispersion,
and modal losses.
Table 2 lists the factors of attenuation and dispersion limit for typical fiber-optic cable.
Table 2
Limits
Attenuation
Dispersion
1. The product of bandwidth and distance must be less than
500 megahertz per kilometer (MHzkm).
Approximating the AIP Power Margin
The LED used for a multimode transmission light source creates multiple propagation paths of light,
each with a different path length and time requirement to cross the optical fiber, causing signal
dispersion (smear). Higher order mode loss (HOL) results from light from the LED entering the fiber
and being radiated into the fiber cladding. A worst case estimate of power margin (PM) for
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.
For SONET versions of the AIP module, the signal must meet the worst case parameters listed
in Table 3.
Table 3
PT
PR
PM
The power budget (PB) is the maximum possible amount of power transmitted. The following
equation shows the calculation of the power budget:
PB = PT – PR
PB = –18.5 – (–30)
PB = –18.5 + 30
PB = 11.5 dB
The power margin (PM) calculation is derived from the power budget minus the link loss (LL), as
follows:
PM = PB – LL
If the power margin is positive, as a rule, the link will work.
Typical Fiber-Optic Link Attenuation and Dispersion Limits
Single-Mode
0.5 dB
No limit
AIP SONET Signal Requirements
Single-Mode Multimode
–18.5 dB –15 dB
–30 dB –28 dB
11.5 dB 13 dB
Asynchronous Transfer Mode Interface Processor (AIP) Installation and Configuration
Multimode
1.0 dB/km
1
500 MHzkm
AIP Installation Prerequisites
9