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6.3 Test Modes
The mDSL Line Driver offers a proprietary Remote Loopback test mode. It also
has a built-in V.52 BER test-pattern generator to evaluate the communication status
between units. Activate this test mode by toggling the Test Mode switch on the
unit’s front panel.
6.3.1 O
VERVIEW
Figure 6-2 shows the major elements used in the loopback and 511 pattern tests
available in the mDSL Line Driver. Each block has several functions. Following
Figure 6-2 are descriptions of the elements during Test Modes.
Figure 6-2. Block diagram: two mDSL Line Drivers
communicating over the DSL span.
• Framer: The framer determines the status of the line. In normal operation,
the framer transmits and expects to receive framed packets from the far end. If
the framer receives framed packets from the far end, the DSL Link LED will
turn on. If framed packets are not received, the DSL Link LED will turn off.
The restart procedure uses this information to determine if a valid connection
is made (cable disconnect, poor cable quality, etc). In normal Data Mode, if
the box receives four seconds of unframed packets it will restart the box and
begin trying to re-establish a connection with the the remote mDSL Line
Driver. The distinction between framed packets and unframed packets
becomes important when we discuss the pattern generator.
• Pattern Gen./Det.: This part of the processor generates and detects the
511/511E patterns. When transmitting 511 patterns, the information is
unframed (because it originates after the framer) and is intended to be
evaluated only by another processor. If the units are transmitting data and the
pattern generator is enabled on one end of the link, the far end will begin
CHAPTER 6: Operation
Framer
Processor
Processor
Framer
Pattern
Gen./Det.
Pattern
Gen./Det.
Loop
Control
Loop
Control
DSL
Span
