18 User Guide
Loopback
The Radiance multi-rate line card features loopback testing capability to help
verify proper operation and to isolate problems within a particular segment of
the network. During loopback, the LBK LED is yellow. Loopback is enabled/
disabled in two ways: (1) setting the LBCK DIP switch(es), or (2) through
software by enabling loopback on Port 1 and/or 2. Once loopback is enabled, the
card remains in this mode until you reset the DIP switch or change the software
setting.

Normal Operation

During normal operation (loopback disabled), data from a local device enters the
local multi-rate line card through Port 1, passes through the fiber line between
the two cards, exits through Port 1 on the remote multi-rate line card, then enters
the remote device. The path is reversed for incoming data to the local device.
Local Multi-Rate
Line Card Remote Multi-Rate
Line Card
Local
Device
Remote
Device
Port
1Port
1
Port
2
Port
2

Local Port Loopback

Loopback can be applied individually to either port on a multi-rate line card.
The following diagrams illustrate the flow of data when loopback is enabled
independently on Port 1 and on Port 2.
Local Multi-Rate
Line Card Remote Multi-Rate
Line Card
Local
Device
Remote
Device
Port
1Port
1
Port
2
Port
2
Local Multi-Rate
Line Card Remote Multi-Rate
Line Card
Local
Device
Remote
Device
Port
1Port
1
Port
2
Port
2