Figure 11: Block Diagram Compact mDSL Modem
Framer
The framer is used to determine 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, CTS and CD will be active. If
framed packets are not received, CTS and CD
will be inactive. 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 Compact mDSL
Modem receives 4 seconds of unframed packets
it will restart and begin trying to re-establish a
connection with the far end. 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
intended to be evaluated only by another
Processor. If the units are in Data Mode and the
pattern generator 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, we force the pattern
generator to time out before it can cause the link
to be killed.
Loop Control
This part of the Processor is used to control
loop-backs. In a Local Loop, the data is looped
back towards the local DTE. In a Remote Loop,
the data is looped back to the line, but it is also
allowed to pass through to the framer and to the
remote DTE.
Pattern
Gen/Det
Loop
Control
Loop
Control
Pattern
Gen/Det
Processor
Processor
Framer
Framer
Line
17
Compact mDSL Modem
18
Compact mDSL Modem
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 Model 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 rea-
son 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
automatically 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
termination of a data path. The direction of the
arrow connected distinguish the two data paths.
This symbol designates an invalid data path. If
there is data present it should be ignored.
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.)
