Evaluating The Power Budget; Managing Receiver Overload - Cisco 10000 Series Troubleshooting Manual

Optical Signal Input/Output Problems
Table 6-1
Card Type
OC-12 Packet Over SONET line card
Gigabit Ethernet line card
1. Mode-conditioning patch cord (CAB-GELX-625 or equivalent) is required. If you use an ordinary patch cord with MMF,

Evaluating the Power Budget

Use the following equation to ensure that an appropriate power budget has been allotted to optical links
terminating at the Cisco 10000 series router.
The power budget (PB) is the maximum possible amount of power transmitted. The following equation
shows the calculation of the power budget:
Where:
Insufficient power budget occurs when the power margin (PM) is less than 0. PM is equal to the power
budget minus the link loss (LL).
Three factors contribute to link loss:
•
•
•
These are typical values; refer to the manufacturer for the actual values.
Note

Managing Receiver Overload

Receiver overload can occur when (PR
receiver power and PT
use an attenuator on the link between any singlemode SONET transmitter and the receiver. Doing so
increases the value of LL.
Cisco 10000 Series Router Troubleshooting Guide
6-2
Optical Fiber Types for Cisco 10000 Series Router Line Cards
1000BaseLX/LH GBICs, and a short link distance (10s of meters), you can cause transceiver saturation, resulting in an
elevated bit error rate (BER). In addition, if you use the LX/LH GBIC with 62.5-micron diameter MMF, you must install a
mode-conditioning patch cord between the GBIC and the MMF cable on both the transmit and receive ends of the link. The
mode-conditioning patch cord is required for link distances greater than 984 ft. (300 m).
PB = PTmin – PRmin
PTmin = Minimum transmitter power
PRmin = Minimum receiver sensitivity
PM = PB – LL
Fiber attenuation (single mode) 0.5 dB/km
Connector 0.5 dB
Splice 0.5 dB
is maximum transmitter power. To prevent overloading the receiver, you can
max
Appropriate Fiber Type
Single mode.
The appropriate fiber type for the gigabit Ethernet
line card is dependent upon the installed GBIC.
1000BaseSX, multimode.
1.
1000BaseLX/LH, single mode and
2.
multimode
1000BaseZX, single mode.
3.
– (PT – LL)) is less than 0, where PRmax is maximum
max max
Chapter 6 Troubleshooting Serial Lines
1
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OL-0439-02