Patton electronic 3088 Series user manual Loopbacks, Patterns

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 <offlalrdl>. The data path for the LAL is shown in figure 22.

511Pattern Generator

511BER

Meter

	.
DSL		DSL
Framer		Framer
	Line

511Pattern Generator

511BER

Meter

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.

511 Pattern		Line
Generator
511 BER	DSL		DSL
Meter
	Framer		Framer

Figure 23. Remote Digital Loopback diagram

511Pattern Generator

511BER

Meter

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 <off511511e>. 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.

Introduction 54