Filter
Top Products
Introduction 54
Model 3088 Series User Manual 4 • Operation
Loopbacks
The 3088 supports both Local Analog Loopbacks (LAL) and Remote Digital Loopbacks (RDL). These can be
initiated either from the optional front panel switches or by the console command dsl set loopback
<off|lal|rdl>. The data path for the LAL is shown in figure 22.
.
Figure 22. Local Analog Loopback diagram
The data received from the serial interface is looped back before going out on the DSL line. Note that this
loopback occurs after the pattern generator/BER meter. This means that running a 511 pattern in conjunction
with an LAL should result in no error detected by the meter.
The data path for the RDL is shown in figure 23.
Figure 23. Remote Digital Loopback diagram
The RDL causes the remote unit to loop the data received from the DSL line back tow the DSL line.
Patterns
The 3088 can generate and detect 511 and 511 with Error patterns. These can be initiated either by the
optional front panel switches or by the console command dsl set pattern <off|511|511e>. When the pattern is
started, the DSL framer uses its internal 511 pattern generator for its DSL TX data instead of the data received
from the serial interface. Also, the framer’s internal BER Meter tries to detect a 511 pattern in the DSL
RX Data.
Because the BER Meter always runs when the pattern generator runs, the meter will detect errors if either the
pattern is not either looped back or the remote unit is not transmitting a 511 pattern.
One point to note is that the way errors are generated in the 511E pattern generates CRC errors. This can
cause the DSL error monitor to restart the link if the thresholds are set low enough.
DSL
Framer
511 Pattern
Generator
511 BER
Meter
DSL
Framer
511 Pattern
Generator
511 BER
Meter
Line
DSL
Framer
511 Pattern
Generator
511 BER
Meter
DSL
Framer
511 Pattern
Generator
511 BER
Meter
Line