Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 8 Troubleshooting the Cisco Catalyst 6509
Troubleshooting Serial Lines
Fiber-Optic Connections
An optical signal I/O problem can be caused by
• Incorrect type of fiber
• Defective fiber
• Transmit (TX) and Receive (RX) fibers reversed
• Insufficient power budget on the optical link
• Receiver overload on the optical link
Be sure to use single-mode fiber for a single-mode interface and multimode fiber for a multimode
interface. Table 8-1 describes fiber types appropriate for each Cisco 10000 ESR line card.
Evaluating the Power Budget
Proper operation of an optical data link depends on modulated light reaching the receiver with enough
power to be demodulated. The power budget (PB) is the difference between transmitter power (PT) and
receiver sensitivity (PR). For instance, if transmitter power is –20 dB and receiver sensitivity is –30 dB,
the power budget is 10 dB:
PB = PT – PR
PB = –20 dB – (–30 dB)
PB = 10 dB
The SONET specification requires the signal to meet the worst-case requirements listed in Table 8-2.
Table 8-1 Optical Fiber Types for Cisco 10000 ESR Line Cards
Card Type Fiber Type
OC-12 Packet over SONET line
card
Single mode
Gigabit Ethernet line card Depends on installed GBIC:
1. 1000BaseSX, multimode
2. 1000BaseLX/LH, single mode and multimode
1
3. 1000BaseZX, single mode
1. A mode-conditioning patch cord (CAB-GELX-625 or equivalent) is required. If you use an ordinary patch cord
with MMF, 1000BaseLX/LH GBICs, and a short link distance (tens 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 transmit and receive ends of the link. The mode-conditioning patch cord is required for link
distances greater than 1000 ft (300 m).
Table 8-2 SONET Signal Requirements
MM SMI SML
Transmitter power –20 dBm –15 dBm –5 dBm
Receiver sensitivity –30 dBm –31 dBm –34 dBm
Power budget 10 dB 16 dB 29 dBm