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DarkStar User Guide
3: Software
www.xkl.com
incoming signal levels fall beneath the module's receiver direction sensitivity threshold, the DarkStar system reports LOS
against that interface. LOS masks Loss of Lock (LOL).
•
Loss of Lock (LOL):
The CDR circuitry is normally locked on the encapsulation or clock frequency assigned to the given
interface. When the CDR circuitry fails to lock on the signal, the DarkStar system may report LOL against the interface. LOL
can occur on an interface's receive or transmit direction.
Use the
show interface
command to view the line status of transport interfaces and detect other fault conditions that can
interfere with data integrity.
3.3.6 Error Forwarding
DarkStar system use LOL forwarding to forward errors and accomplish the following:
•
Protect DarkStar wave interfaces from variations in power levels caused by noise or invalid client interface signals.
•
Facilitate consistent DarkStar error states when an interface detects an upstream signal integrity problem.
•
Facilitate consistent signal integrity error detection by client-connected systems when upstream signal integrity problems
are detected.
•
For interfaces with virtualight enabled, LOL forwarding disables the downstream interface transmitter.
•
For interfaces with virtualight disabled, LOL forwarding sends a signal to the downstream interface when a signal integrity
error is detected upstream. The error forwarding signal stabilizes transmitter power levels, avoiding damage to DWDM
transmitters/receivers. The signal integrity error is detected consistently further downstream.
Some modules may report incorrect statuses when error forwarding occurs. Therefore, it may be possible for different
modules, even if the modules are the same model, to report different line statuses.
In the absence of client signals, error forwarding across the wave interfaces may result in client equipment reporting unusual
errors, such as a loss of frame.
XKL recommends leaving Virtualight mode enabled for client interfaces, which is its default setting. If client interfaces are set
up with loopbacks and they have Virtualight disabled, the interfaces may cycle rapidly between up and down states.
The error forwarding state of an interface is displayed by the
show interface
command. For interfaces not connected to
another interface on the switch board, the
show interface
command may report
Error Forwarding Enabled
or
Laser Shutdown by virtualight
Use the virtualight commands available in configuration mode to configure transport interface error forwarding and control.
When a transport interface is shut down with
laser shutdown
and restarted with
no laser shutdown
, some lasers
may briefly display a
Down
line status and a
Fault
alarm status in the show interface display. This result is usually a transient
condition and does not represent a problem with the laser. If you run
show interface
again a few seconds later, the line
will be up and its alarm status will no longer be
Fault
.
3.4 BERT (Bit Error Ratio Test)
The Bit Error Ratio (BER) is an important measure of the transmission quality of an interface. BER is the ratio of the bit error
count to the total transmitted bit count.
BER = (bit errors) / (bit total)
