SFP Module Connection Issues in Fiber Optic Networks

Lack of Connectivity Between SFP Modules When Connecting Buildings via Fiber Optic

Lack of connectivity between SFP modules when connecting buildings via fiber optic can be caused by several typical issues, including module incompatibility, connector contamination, incorrect polarity, or switch configuration problems. For diagnosis, you need to sequentially check the physical connection, module parameters, port configuration, and optical signal status.

Contents

• Main Reasons for Lack of Connectivity
• Step-by-Step Problem Diagnosis
• Solving Common Malfunctions
• Equipment Compatibility Check
• Diagnostic Tools
• Connection Recommendations
• Troubleshooting Checklist

Main Reasons for Lack of Connectivity

Lack of connectivity between SFP modules when connecting buildings via fiber optic can be caused by the following main reasons:

1. Module parameter incompatibility - Although you’re using identical OSNOVO SFP-S1LC13-G-1550-1310 modules, it’s important to ensure they are properly recognized by the D-Link switches.

2. Optical connector contamination - This is one of the most common causes of fiber optic problems. Connector contamination can significantly weaken or completely block the optical signal.

3. Incorrect connection polarity - When using WDM (Wavelength Division Multiplexing) with different wavelengths (1550nm TX, 1310nm RX), it’s important to properly connect the connectors.

4. Optical power issues - Even when light passes through the fiber (as you checked with a flashlight), the actual optical power may be insufficient for proper operation.

5. Switch configuration issues - Switch ports may be in an err-disabled state or have incorrect settings.

Step-by-Step Problem Diagnosis

1. Visual Inspection of Connections

Start by checking the physical condition of the connections:

• Inspect SFP module connectors for visible damage or contamination
• Ensure all connector latches are fully secured
• Make sure the fiber optic cable has no kinks or damage
• Verify that patch cords are correctly connected to the cross-connect

Important: Do not use a regular flashlight for testing - it won’t show the actual quality of the optical signal. Professional optical testers are required for diagnosis.

2. Equipment Compatibility Check

Research data shows that OSNOVO SFP-S1LC13-G-1550-1310 modules are designed to work with:

• Single Mode cables
• Transmission distances up to 20 km
• Speeds up to 1.25 Gbit/s
• LC connectors
• WDM technology (1550nm TX, 1310nm RX)

Ensure that the D-Link DGS-1250-28X and DGS-1250-52X switches support the SFP modules being used and have appropriate port settings.

3. Switch Port Status Verification

Execute the following commands on the switches for diagnosis:

show interface status
show interface gigabitethernet X/X
show transceiver details
show interface counters errors

These commands will help determine:

• Port status (up/down)
• Presence of errors on interfaces
• SFP module recognition details
• Transmission error statistics

4. Optical Power Measurement

For accurate diagnosis, you need to measure optical power at both ends of the line:

• Transmitter (TX) power measurement should show a level of approximately -3 to -5 dBm
• Receiver (RX) power measurement should match the module sensitivity (22 dBm for OSNOVO)

Insufficient optical power can be caused by:

• Connector contamination
• Cable damage
• Use of poor quality patch cords
• Line length that is too long

Solving Common Malfunctions

1. Cleaning Optical Connectors

Research shows that connector contamination is one of the most common causes of SFP module problems:

Connector cleaning: Use a special optical cleaning pen for cleaning LC/SC connectors. Thoroughly clean both ends of the connection.

Cleaning process:

1. Disconnect the cable from the SFP module
2. Use an optical cleaner to clean the connector
3. Repeat the procedure for the second end
4. Reconnect the cable and check the result

2. Verifying WDM Connection Correctness

OSNOVO SFP-S1LC13-G-1550-1310 modules use WDM technology with different wavelengths for TX and RX:

• Transmission (TX): 1550 nm
• Reception (RX): 1310 nm

Ensure that modules with identical parameters are used at both ends of the connection. If one end uses a module with TX 1550nm/RX 1310nm and the other uses TX 1310nm/RX 1550nm, connectivity will not work properly.

3. Equipment Reboot

Sometimes a simple reboot can solve the problem:

1. Reboot the switches
2. Reinstall the SFP modules into the ports
3. Check how the equipment recognizes the modules after reboot

4. Switch Configuration Verification

Configure switches for proper operation with fiber optic connections:

• Ensure ports are not in err-disabled mode
• Check speed and duplex settings
• Disable power saving features on optical ports
• Check for restrictions on unauthorized SFP modules

Equipment Compatibility Check

OSNOVO SFP-S1LC13-G-1550-1310 Compatibility

Research data shows that these modules have the following specifications:

• Type: Single Mode
• Speed: Up to 1.25 Gbit/s
• Transmission distance: Up to 20 km
• Optical budget: 13 dB
• Receiver sensitivity: 22 dBm
• Supply voltage: 3.3 V DC
• Current consumption: Less than 280 mA

D-Link Switch Compatibility

D-Link DGS-1250-28X and D-Link DGS-1250-52X switches should support:

• Standard SFP modules
• Speeds up to 1 Gbit/s and higher
• Automatic parameter detection of modules
• DDM/DOM support for status monitoring

If switches do not recognize the modules, a firmware update may be required or verification of restrictions on third-party SFP modules may be necessary.

Diagnostic Tools

Essential Diagnostic Tools:

1. Optical Power Meter

   • For measuring actual optical power
   • Allows determining signal level in dBm

2. Light Source

   • For verifying fiber integrity
   • More precise than a regular flashlight

3. Optical Cleaner

   • Special pen cleaners for LC/SC connectors
   • Lint-free wipes for optics

4. Optical Microscope

   • For visual inspection of connector condition
   • Detection of micro-cracks and contamination

Software Diagnostic Tools:

Use commands built into switches for diagnosis:

• show transceiver details - detailed module information
• show interface status - interface status
• show interface counters - error statistics
• show logging - system messages and errors

Connection Recommendations

Proper Connection Sequence:

1. Equipment Preparation:

   • Ensure all cables and modules are functional
   • Verify connector cleanliness before connection
   • Allow switches to fully boot up

2. Connection Process:

   • Install SFP modules in appropriate ports
   • Connect optical patch cords to modules
   • Connect cable ends on the cross-connect panel
   • Connect the other ends of patch cords to switches

3. Connectivity Verification:

   • Monitor port status via command line
   • Check for LED indication on SFP modules
   • Use ping commands to verify accessibility

Preventive Measures:

1. Regular Connector Cleaning

   • Clean connectors every 3-6 months
   • Use only specialized cleaning supplies
   • Avoid touching working connector surfaces

2. Contamination Protection

   • Use protective caps on unused connectors
   • Store cables in clean places
   • Avoid working with optics in dusty areas without protection

Troubleshooting Checklist

Basic Checks:

• [ ] Visual Inspection - No visible damage to cables or modules
• [ ] Connector Cleaning - Cleaning LC connectors with optical cleaner
• [ ] Power Check - Switches are receiving power, modules are recognized
• [ ] Parameter Matching - Both modules have identical characteristics
• [ ] Cable Quality - Cable meets Single Mode requirements
• [ ] Line Length - Does not exceed 20 km for used modules
• [ ] Connection Polarity - Correct WDM module connection
• [ ] Port Configuration - Ports not in err-disabled mode
• [ ] Optical Power - Measure TX/RX power levels
• [ ] Switch Firmware - Latest firmware version

Additional Checks:

• [ ] Test with Different Cable - Use a known working cable
• [ ] Test with Different Port - Move modules to other ports
• [ ] Test with Different Equipment - Connect to other switches
• [ ] Cross-Connect Verification - Rule out cross-connect problems
• [ ] Electromagnetic Interference Check - No strong interference near cable

Sources

1. GLGNET - Why Is My SFP Port Not Working? Common Issues and Fixes
2. Excentis - SFP+ compatibility issues? Here are 5 troubleshooting tips!
3. FS Community - How to Troubleshoot A Fiber Optic Transceiver
4. Switch SFP - 5 troubleshooting tips for connecting the SFP’s
5. DSSL - OSNOVO SFP-S1LC13-G-1550-1310: SFP module for connecting to a switch via fiber optic
6. OSNOVO - SFP-S1LC13-G-1550-1310 - SFP modules, description with photos and application diagram
7. Cisco Meraki - Basic SFP Troubleshooting Guide
8. Reddit - r/networking on Troubleshooting Fiber Cables

Conclusion

Lack of connectivity between SFP modules when connecting buildings via fiber optic is most often caused by connector contamination, module parameter incompatibility, or incorrect equipment configuration. To successfully resolve the issue, you need to perform diagnosis sequentially, starting with checking physical connections and cleaning connectors, then proceeding to equipment compatibility verification and optical power measurement.

It is recommended to regularly perform preventive maintenance of optical equipment, use only verified cables and modules, and have the necessary tools for diagnosing optical lines available. For complex malfunctions, always consult the equipment’s technical documentation or contact fiber optic network specialists.