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5.2 TEST MODES
The 3088RC offers test modes in the form of loopbacks, PRBS pattern
generators, and combinations of both (see Figure 17 on page 45).
Figure 18 is a block diagram of the Model 3088RC with respect to test
modes.
Figure 18. 3088RC Block Diagram
Loopbacks
The 3088RC 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 19.
Figure 19. 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 gen-
erator/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 20.
Figure 20. Remote Digital Loopback Diagram
The RDL causes the remote unit to loop the data received from the DSL
line back to the DSL line.
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
DSL
Framer
511 Pattern
Generator
511 BER
Meter
DSL
Framer
511 Pattern
Generator
511 BER
Meter
Line