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Overview
Figure 13 shows the major elements used in the loop-back and pattern
tests available in the Model 1088. Each block has several functions. Fol-
lowing Figure 13 are descriptions that show how the elements are used
during Test Modes.
Figure 13.
Block Diagram Model 1088
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 pro-
cedure uses this information to determine if a valid connection
is made (cable disconnect, poor cable quality, etc). In normal
Data Mode, if the Model 1088 receives 4 seconds of unframed
packets it will restart and begin trying to re-establish a connec-
tion 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 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 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.
Restart Procedure and Time Outs
The restart procedure is in place to allow the units to re-estab-
Pattern
Gen/Det
Loop
Contr
ol
Loop
Contro
l
Pattern
Gen/Det
Processor
Processor
Framer
Framer
Line