Specifications

4-3
Cisco ONS 15530 Planning Guide
OL-7708-01
Chapter 4 Optical Loss Budgets
Overall Optical Loss Budget
Calculating Optical Loss Budgets
Using the optical loss characteristics for the Cisco ONS 15530 components, you can calculate the optical
loss between the transmitting laser on one node and the receiver on another node. The general rules for
calculating the optical loss budget are as follows:
• The maximum power loss between the nodes cannot exceed the minimum transmit power of the laser
minus the minimum sensitivity of the receiver and network-level penalty.
Note Determine the proper network-level penalty to the receive power based on your actual
network topology characteristics, such as dispersion.
• The minimum attenuation between the nodes must be greater than the maximum transmitter power
of the laser minus the receiver overload value.
The following example shows how to calculate the optical loss budget for 2.5-Gbps data channels using
the values in Table 4-1:
• The power loss between the transmit laser and receiver must not exceed 33 (5 – (–28)) dB or the
signal will not be detected accurately.
• At least 18 (10 – (–8)) dB of attenuation between neighboring nodes prevents receiver saturation.
To validate a network design, the optical loss must be calculated for each band of channels. This
calculation must be done for both directions if protection is implemented, and for the OSC between each
pair of nodes. The optical loss is calculated by summing the losses introduced by each component in the
signal path.
At a minimum, any data channel path calculation must include line card transmit loss, channel add loss,
fiber loss, channel drop loss, and line card receive loss (see Figure 4-1). In ring topologies, pass-through
losses must be considered. Losses due to external devices such as fixed attenuators and monitoring taps
also need to be included.