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CHAPTER 6: Operation
Figure 6-2. Block diagram of the major elements used in the tests.
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 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 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/E data is looped back to the line and to the remote unit
over the DSL span.
Framer
Processor
Processor
Framer
Pattern
Gen./Det.
Pattern
Gen./Det.
Loop
Control
Loop
Control
DSL
Span
