3Com 155 PCI manual Constructing Loopback Plugs, Fiber-Optic Loopback Plug

6-16 CHAPTER 6: DIAGNOSTICS AND TROUBLESHOOTING

Constructing Loopback Plugs

To run the external loopback test, you must first insert a loopback plug into the cable connectors of the 3C975 ATMLink NIC. The following instructions describe how to construct a loopback plug for the 3C975-F and the 3C975-UTP ATMLink NICs.

Fiber-Optic Loopback Plug

The loopback plug lets the ATMLink NIC to transmit and receive on a closed loop. A fiber-optic loopback plug for the 3C975-F NIC may be constructed from a single strand or a double strand of standard fiber-optic cable.

To construct a loopback plug from a single strand of fiber-optic cable, insert the male connectors at both ends of the cable into the female connectors on the NIC.

To construct a loopback plug from a double-strand fiber-optic cable, uncouple the connectors at both ends of the cable, and insert the two male connectors of one of the strands into the connector ports on the NIC. A double-strand fiber-optic cable has writing on one of the strands in the pair, but not on the other.

The following procedure for creating a loopback plug from a common type of double-strand cable is provided for your reference. The way the connectors clip together may vary with the manufacturer.

1Unclip the connectors at both ends of the double-strand cable, as shown in Figure 6-10.

2Clip together the connectors of one of the strands (one strand has markings on it, the other does not), as shown in Figure 6-11.

3Insert the connectors into the SC connector ports of the 3C975-F ATMLink NIC.