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Section 3, Configuration
Network Interface
• Loop
• Free-Run
• External Nonrevertive
• External Revertive
Loop
Loop timing configures the unit to recover timing from the STS-1 receive signal. Loss of the STS-1 receive
signal or reception of AIS causes the unit to enter hold-over mode (refer to
information on hold-over mode). The STS-1 receive signal must be valid for at least 10 seconds for the unit
to exit hold-over mode and restore loop timing.
Free-Run
When the unit is configured for Free-Run timing mode, timing is derived from a +/–20 ppm internal refer-
ence providing a SONET Minimum Clock (SMC).
External Nonrevertive
Setting the unit to External Nonrevertive or External Revertive timing mode configures the unit to derive
timing from one of the two external sources selected in the Primary External Clock (
ary External Clock
(Sec Ext)
sets of wire-wrap pins on the back of the MX2800 chassis. The external clock source may be disabled (if
only one source exists, or no external clock sources are desired). When both sources are configured, failure
of one source causes the unit to switch to the other source (if it is a valid source).
When in External Nonrevertive timing mode, the timing source does not switch back to the Primary exter-
nal clock in the event that it becomes available.
External Revertive
When in External Revertive timing mode, the timing source switches back to Primary External clock if it
becomes available.
Failure of both sources causes the unit to enter hold-over mode. At least one external clock source must be
valid for at least 10 seconds for the unit to exit hold-over mode and restore external clock timing.
XCV Threshold
The XCV Threshold (excessive code violations threshold) sets a limit on code violations accepted by the
unit before it switches controller cards. If set to Disabled, code violations do not cause the unit to switch
controller cards. The threshold limits are described in the following chart:
Setting
The unit switches controller cards if...
-3
1E
more than one out of every 1,000 bits received on the STS-1 contains a code violation
-4
1E
more than one out of every 10,000 bits received on the STS-1 contains a code violation
-5
1E
more than one out of every 100,000 bits received on the STS-1 contains a code violation
-6
1E
more than one out of every 1,000,000 bits received on the STS-1 contains a code violation
3-6
options. These are external BITS clocks that may be terminated on the two
MX2800 STS-1 User Manual
Loop Mode
on page 1-4 for
) and Second-
PRI Ext
61204659L1-1A
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