Verilink 1558D (34-00255) Product Manual - Manual (Page 19)

Operation 3-3 1558D APS CSU/DSU
APS Switching Parameters
The 1558D unit switches from the active line to the standby
line based upon user definable alarm parameters. The alarm
performance parameters that can configured by the user are
Errored Seconds, Consecutively Severely Seconds, Loss of
Signal, and Loss of Framing. These alarm parameters and
their definition are described below.
Errored Seconds (ES) - The user can define that the 1558D
switches from the active line to the standby line when a cer-
tain number of errored seconds have been detected during
the current 15 minute performance interval (900 seconds).
The ES threshold can be set from 0 (setting this parameter to
a zero value disables ES switching) to 900 seconds. The
1558D is configured at the factory with 20 errored seconds
as the default errored second value. The definition of an ES
is a second containing one or more CRC errors.
Consecutive Severely Errored Seconds (CSES) - Custom-
ers can define the 1558D switches from the active line to the
standby line when a certain number of Consecutive Severely
Errored Seconds have been detected during the current 15
minute performance interval (900 seconds). The CSES
threshold can be set from 0 (setting this parameter to a zero
value disables CSES switching) to 900 seconds. The 1558D
is configured at the factory with 2 consecutive severely
errored seconds as the default CSES value. The definition of
a CSES is when two or more consecutive SES have been
detected (note that CSES are transparent to the boundary
between 15 minute intervals). A severely errored second is
defined as a second containing 320 or more ESF errors.
Loss of Signal (LOS) - The user can define that the 1558D
switches from the active line to the standby line when a loss
of signal state has been detected. The 1558D is shipped
from the factory with loss of signal parameter enabled. The
definition of a loss of signal is when the receive signal from
the network contains
≥
175 consecutive bit intervals contain-
ing all zeros (no pulses). The condition will be cleared when
one or more intervals contain a one.
Loss of Frame (LOF) - The user can define that the 1558D
switches from the active line to the standby line when a loss
of frame error state has been detected. The 1558D is shipped
from the factory with the loss of frame parameter enabled.
An LOF alarm condition occurs when 32 or more consecu-
tive ESF frames contain frame bit errors.
When the current count of either ES or CSES is greater than
or equal to the threshold setting or when a LOS or LOF (if
enabled) is detected, the service shall be transferred from
the active path to the standby path as long as the standby
path is available (not in an alarm state or in a looped state).
A requirement for the standby path to be available is that the
timer circuitry, described below, is not active and a LOS or
LOF condition does not exist.
Line Availability Timer
The line availability timer is used to quantify when a path is
eligible to accept service.Line availability is determined by
the APS by observing a defined window of time in which no
active error events have occurred. The APS line availability
timer can be set to any value from 0-900 seconds. This
value represents the minimum amount of time, free of active
error events, that must expire before this path is declared as
ready to accept service. The factory default setting for the
line availability timer is 60 seconds.
The line availability timer requires storage for the timer set-
ting and the active timer count. If the timer setting is 0, the
timer circuitry is disabled and the path is always available
for service, assuming that there are no active alarm condi-
tions present. If the timer setting is set to a value ranging
from 1 to 900 seconds and a service transfer takes place, the
standby unit initializes the active timer count to the timer
setting. When the timer expires, this standby path becomes
available for a service transfer. This timed period must be
free of errors for all active events. If an error occurs, the
active timer count is reset.
When operated in the optional revertive mode, the path
availability timer serves to force restoration of service back
to the default access, Path A. That is, when service is
switched from Path A, it will remain on the standby path
(Path B) only until Path A’s availability timer expires. The
factory default is Revert set to OFF.
Status and Performance Information
The current status and performance parameters are stored in
the internal registers of the 1558D. Access to this informa-
tion is via the 1559 APSM site manager (optional) or the
LAPS (local access protection switch) PC software. The
LAPS software is shipped with each 1558D unit.
The following information can be viewed by the user using
either the 1559 APS Site Manager or the provided APS
Local Access DOS Software.
• This path is currently carrying the service.
• This path is currently in a failed state.
• This path is currently in an inhibit state.
• The LB of this path is currently activated.
• The other path is currently in a failed state.
• The other path is currently in an inhibit state.
• The LB of the other path is activated.
• The manual locked control state.
• Current status
• Current interval Occurrences
• Current interval Duration
• Current Interval Timer