User Guide: Technical Reference SECTION 4 NETWORK MANAGEMENT FOR
ioLink 4
PRELIMINARY
Customer Support (202) 333-7031
4-3
The
ioWave
Management Information Base (MIB) includes several options for placing the modem into a
loopback mode. These modes are useful for testing sub-sections of the modem when attempting to
isolate a failure. The subsections that are present are the Line Interface Unit (LIU), the Forward Error
Correction (FEC) unit, the Baseband processing section and the Intermediate Frequency (IF) section. A
useful means for performing tests of the modem is to use a Bit Error Rate Tester (BERT) as the input
device. The specific test modes that may be configured via the front panel or the agent are:
•
LIU Loopback:
There are three loopback modes available from within the line interface section of the
modem.
1. Local
The data from the far end of the link is looped back to it as well as passed through to the
DSX or G.703 interface of the near-end modem. Input from the near-end DSX or G.703 interface
is ignored. By setting the far-end modem into this mode, a test of the complete link may be made.
2. Remote
The data from the user device connected to the DSX or G.703 interface is looped
back to it as well as passed through the modem to the far end of the link. Data from the far end of
the link is ignored. This is useful for testing the line interface unit of the near-end modem.
3. Network
The line interface chip looks at the data stream received from the DSX or E1
interface for the NLOOP enable and disable data patterns. When the enable pattern is repeated
for five seconds, the modem is placed into remote loopback (as above). The modem is removed
from this loopback mode by receiving the NLOOP disable pattern for five seconds or by turning
the network loopback mode off.
•
FEC Loopback:
When the modem is in FEC loopback mode, the input data passes through the line
interface unit, the FEC encoder, the FEC decoder and then the line interface unit. This allows the
user to determine whether the line interface and forward error correction sections of the modem are
operating correctly.
