Specifications

CHAPTER
4-1
Cisco ONS 15530 Planning Guide
OL-7708-01
4
Optical Loss Budgets
The optical loss budget is an important aspect in designing networks with the Cisco ONS 15530. The
optical loss budget is the ultimate limiting factor in distances between nodes in a topology. This chapter
contains the following major sections:
• About dB and dBm, page 4-1
• Overall Optical Loss Budget, page 4-2
• Optical Loss for Transponder Line Cards, page 4-4
• Optical Loss for 2.5-Gbps ITU Trunk Cards, page 4-5
• Optical Loss for 10-Gbps ITU Tunable and Non tunable Trunk Cards, page 4-6
• Optical Loss for OADM Modules, page 4-6
• Optical Loss for PSMs, page 4-7
• Client Signal Latency on Aggregation Card, page 4-7
• Fiber Plant Testing, page 4-10
Note The optical specifications described in this chapter are only for the individual components and should
not be used to characterize the entire network performance.
Note The information in this chapter applies only to nonamplified network design.
About dB and dBm
Signal power loss or gain is never a fixed amount of power, but a portion of power, such as one-half or
one-quarter. To calculate lost power along a signal path using fractional values, you cannot add 1/2 and
1/4 to arrive at a total loss. Instead, you must multiply 1/2 by 1/4. This makes calculations for large
networks time-consuming and difficult.
For this reason, the amount of signal loss or gain within a system, or the amount of loss or gain caused
by some component in a system, is expressed using the decibel (dB). Decibels are logarithmic and can
easily be used to calculate total loss or gain just by doing addition. Decibels also scale logarithmically.
For example, a signal gain of 3 dB means that the signal doubles in power; a signal loss of 3 dB means
that the signal halves in power.