User guide

140 RealCT Direct API Developer Guide
Chapter 4: E1 Networking
Using Loopbacks
Loopback configurations loop data back to where it originated.
These configurations help troubleshoot where errors occur.
There are several forms of loopbacks, depending on what you
want to test.
Set software loopbacks using CONFIG_CARRIER as described
in Configuring the Carrier on page 105. There are two software
loopbacks:
Test whether the board’s receiver and transmitter work
properly using a local loopback. In this mode, the board
receives the same data it transmits without passing
through any cabling. To do a local loopback, set the
loopback mode in CONFIG_CARRIER to local.
Test the cabling and verify that the CO can send and
receive valid data using a remote loopback. In this mode,
the board immediately transmits all data it receives back
to the CO. To do a remote loopback, set the loopback mode
in CONFIG_CARRIER to remote.
Figure 22 shows remote and local loopbacks.
Figure 22. Remote and Local Loopbacks in E1
Board
Board CSU
Data stream to trunk A
Data stream from trunk A
CO
Remote Loopback
Local Loopback