Test Modes
The Compact mDSL Modem offers a proprietary Remote
Loopback test modes, plus 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 front panel of the unit.
Overview
Figure 10 below shows the major elements used in the loop-back
and 511 pattern tests available in the Compact mDSL Modem. Each
block has several functions. Following Figure 10 are descriptions of the
elements during Test Modes.
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 4 sec-
onds of unframed packets it will restart the box
and begin trying to re-establish a connection
with the the remote Compact mDSL Modem.
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 transmit-
ting 511 patterns, the information is unframed
(because it originates after the framer) and is
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Compact mDSL Modem
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Compact mDSL Modem
intended to be evaluated only by another Processor.
If the units are transmitting data and the pattern gen-
erator is enabled on one end of the link, the far end
will begin receiving unframed packets and assume
that the line has gone down. During test modes, the
pattern generator is forced to time out before it can
cause the DSL link to go down.
Loop Control
This part of the Processor is used to control Remote
Loopback test mode. In a Remote Loop, the
511/511/Edata is looped back to the line and to the
remote unit over the DSL span.
Restart Procedure
The restart procedure is in place to allow the
and Time Outs
units to re-establish a connection after the framer
begins seeing unframed packets. The Test Mode
Timing Chart below shows the amount of time the
framer must see consecutive unframed packets
before the unit will restart and try to establish a new
line connection. The reason that there are different
Restart Times will become apparent after reading the
rest of the document. The 511/511E Time Out shown
refers to the amount of time the 511/511E pattern will
be valid. At the end of this time the pattern will auto-
matically turn itself off and the normal data path will
be re-established. The ER led will flash indicating to
the user that the test has timed out. The ER led will
stop flashing once the 511/511E switch is placed into
the normal position.
Symbol Indicators
This symbol designates the origination or the termi-
nation of a data path. The direction of the arrow con-
nected distinguish the two data paths.
This symbol designates an invalid data path. If there
is data present it should be ignored.
Pattern
Gen/Det
Loop
Control
Loop
Control
Pattern
Gen/Det
Processor
Processor
Framer
Framer
DSL
Span
Figure 10:
Block Diagram- Two Compact mDSL Modems Communicating Over the DSL Span
Test Mode Timing
Item
Elapsed Time (seconds)
Start Up
50
Data Mode
4
511/511E Generator Enabled 60 (The generator will stop after 45 seconds.)
Remote End of an RDL
60
511/511E Time Out
45 (The pattern generator will automatically turn
off after 45 seconds. The ER LED will flash until
the user turns off the 511/511E switch.)
