Cisco 7000 Series Hardware Installation And Maintenance Manual page 72

Site Requirements
Multimode Power Budget Example with Sufficient Power for Transmission
The following is an example multimode power budget calculation based on the following variables:
Estimate the power budget as follows:
The value of 2.5 dB indicates that this link would have sufficient power for transmission.
Multimode Power Budget Example of Dispersion Limit
Following is an example with the same parameters as the previous example, but with a multimode
link distance of 4 km:
The value of 1.5 dB indicates that this link would have sufficient power for transmission. However,
due to the dispersion limit on the link (4 km x 155.52 MHz > 500 MHzkm), this link would not work
with multimode fiber. In this case, single-mode fiber would be the better choice.
Single-Mode Transmission
The single-mode signal source is an injection laser diode. Single-mode transmission is useful for
longer distances, because there is a single transmission path within the fiber and smear does not
occur. In addition, chromatic dispersion is also reduced because laser light is essentially
monochromatic.
The maximum overload specification on the single-mode receiver is –14 dBm. The single-mode
receiver can be overloaded when using short lengths of fiber because the transmitter can transmit up
to –8 dB, while the receiver could be overloaded at –14 dB, but no damage to the receiver will result.
To prevent overloading the receiver connecting short fiber links, insert a 5 to 10 dB attenuator on the
link between any single-mode SONET transmitter and the receiver.
2-12 Cisco 7010 Hardware Installation and Maintenance
Length of multimode link = 3 kilometers (km)
4 connectors
3 splices
Higher order loss (HOL)
Clock recovery module (CRM)
PB = 11.5 dB – 3 km (1.0 dB/km) – 4 (0.5 dB) – 3 (0.5 dB) – 0.5 dB (HOL) – 1 dB (CRM)
PB = 11.5 dB – 3 dB – 2 dB – 1.5 dB – 0.5 dB – 1 dB
PB = 2.5 dB
PB = 11.5 dB – 4 km (1.0 dB/km) – 4 (0.5 dB) – 3 (0.5 dB) – 0.5 dB (HOL) – 1 dB (CRM)
PB = 11.5 dB – 4 dB – 2 dB – 1.5 dB – 0.5 dB – 1 dB
PB = 1.5 dB