Identifying Physical Layer Problems
Cabling faults – fiber and coax

All fiber links are crossed over. The connectors are always the same on stations and infrastructure equipment, so the TX output is connected to the RX input through careful attention to the cable polarity. Check fiber for swapped RX/TX connections when polarized or small form factor multi-fiber connectors are not used. Figure shows the coaxial cable and Figure shows the fiber-optic cable.

If a fiber power test fails, inspect and clean all connections on the link. While walking the cable run route, watch for excessively tight bends and over tightened cable ties that cause micro bends.

Test fiber for power level and link indicator LEDs.

Coaxial Cable
Problems with coaxial cable often occur at the connectors. When the center conductor on the coaxial cable end is not straight and of the correct length, a good connection will not be achieved.

When the center conductor is not straight or is not the correct length, cut the coaxial cable behind the connector end, and strip the insulation back. Make sure that the newly exposed center conductor is straight. Before replacing the new cable connector end, check the general condition of the cable. Make sure that the new cable conductor end is securely crimped to the cable. The center connector should extend 3.2 mm (1/8 inch) beyond the end of the connector.

Check that the coaxial cable end is securely screwed onto the F-connector at the back of the cable access router. Hand-tighten the connector, making sure that it is finger tight; then give it a 1/6 turn.