User`s guide

Device Management
7-6
6700-A2-GY31-70
July 1999
If the selected device is a DSU and the Dial Backup Module selection is No, the
VF status menu item is disabled.
The VF impairments are listed in the left portion of the window. To the right of
each impairment is a bar graph displaying the current status of the impairments.
The device reports the VF conditions; NMS performs the analysis using the
user-defined limits.
The user-defined limits, set within NMS, are shown as up arrows below each bar
graph (see
Defining Thresholds for VF Impairments in Chapter 4, Configuration ).
The number to the side of each arrow represents the limit’s numeric value.
Numeric values to the left of an arrow indicate a lower limit. Numeric values to the
right of an arrow indicate an upper limit. Use the scroll bar to view those VF
impairments not currently displayed within the window. Just below the VF Status
title bar is the time the last sample was received.
To start the collection of impairments, choose Execute. To pause (freeze) the
display, choose Pause. The display stops updating the VF Status and Resume
replaces Pause. To continue updating the display, choose Resume.
Table 7-3 lists the VF impairment types with a brief description of each; VF
impairments display is device dependent.
Table 7-3. VF Impairments (1 of 2)
VF Impairment Name
Description
Receive Level Expressed in decibels referenced to one milliwatt (dBm); the
actual strength of the received signal.
Signal/Noise Ratio Expressed in decibels (dB), the ratio of the amplitude of the
signal plus the noise to the amplitude of the noise.
Phase Jitter
(20–300 Hz)
Expressed in degrees, the amount of phase difference
(out-of-phase) between the transmitted carrier signal and the
received carrier signal.
Non-Liner Distortion Expressed in dB, the portion of the channel output that is
nonlinear in relation to the input signal. Harmonic and
intermodulation distortion would cause this kind of distortion.
Frequency Offset Expressed in Hertz (Hz), the difference between the
transmitted carrier frequency and the received carrier
frequency.
Gain Hits The number of positive or negative gain hits during the
previous 15 minutes. A gain hit is a three dB change lasting
more than four milliseconds.
Phase Hits The number of phase hits during the previous 15 minutes. A
phase hit is a phase change to a 1004 Hz test signal greater
than 20 degrees.
Impulse Noise The number of impulse hits during the previous 15 minutes.
An impulse hit is a voltage surge of within six dB of the normal
carrier level lasting more than four milliseconds.
Drop Outs The number of dropouts during the previous 15 minutes. A
dropout is a normal carrier level decrease greater than
12 dB lasting more than four milliseconds.
Retrains The number of retransmissions during the previous
15 minutes.