Symmetricom SDU-2000, User Manual

Page: 146 / 470

Input Module Reference Data
1-Port and 3-Port E1 Input Modules
146 SSU-2000 User’s Guide 12713020-002-2 Revision D – April 2004
The firmware running in the E1 Input module performs the following functions:
Determines module type (distinguishes between E1 and DS1 frame chips)
Supports unframed clock signals at the following rates: 1 MHz, 1.544 MHz, 2.048
MHz, 5.0 MHz, 10.0 MHz
Enables/disables the Input module on command (when disabled, it does not
report any alarms or measurement data and blinks the STATUS LED repeatedly)
Enables or disables individual ports on command (disabled ports clear all existing
alarms and do not report any additional alarms or measurement data)
Maintains a provisioned SSM for each port
Stores a priority for each port
Three-Sigma Test
The Input module uses a three-sigma test as part of the phase averaging algorithm
in order to avoid the use of erroneous phase readings. In such tests, the standard
deviation sigma of the phase readings is maintained. Any reading which falls more
than three sigma above or below the mean is considered erroneous.
MTIE Calculation
MTIE is a measurement of the relative noisiness of an input signal. The Input
module automatically (without user intervention) calculates MTIE for its inputs in
accordance with the specifications in (ANSI) T1.101 and reported on demand for a
24 hour period.
MTIE data is retrieved on hour boundaries, though the stop time used may be
current time. Reported time periods include: 0.05, 0.1, 1.0, 10.0, 100.0, 1000.0,
10000.0, and 100000.0 seconds.
MTIE Alarms
The Input module monitors the ongoing MTIE calculations and logs an alarm if the
MTIE calculation for any of several window sizes exceeds user-set masks.
The input module software maintains two alarm masks, each with thresholds at 10,
100, 1000, 10,000, and 100,000 seconds. MTIE readings which violate either mask
at any point cause an alarm at a user-set level (Minor, Major, or Critical). Refer to
Changing Factory Defaults , on page 100, for more information on setting alarm
levels.
Although MTIE is continuously calculated against both clocks, MTIE alarms are
logged only if the measurements against the currently selected clock violate one of
the MTIE alarm masks.