VeEX MTT-14B, Руководство пользователя

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Number of
pulses
(since last
substitution).
Polarity of Previous Pulse
Even
(substitute
B00V)
1 0 0 1 1 0 0 1
Odd
(substitute
000V)
0 0 0 1 0 0 0 1
Figure 59 HDB3 Encoding
The E1 module can be configured to detect the one of the two
types of HDB3 substitution codes, even if they are not matched
to the proper number of pulses since the last substitution.
4.2.6 Signal Levels
Ideal Pulse Actual Pulse G.703 Mask
Figure 60 Pulse Shape
Once a signal has been encoded into a binary format and as
-
sembled into a bit stream, the pulses in the bit stream are then
converted to actual voltage levels suitable for E1 transmission.
In Figure 59, a typical signal level for an E1 pulse with 75 W im-
pedance is either ± 2.37 volts (for a binary 1 value) or 0 volts (for
a binary 0 value). Real-world values are typically ± 10%. Ideally,
each pulse transmitted would be perfectly symmetrical. However,
in the real-world, each pulse is slightly distorted when generated
and more so when it travels down the line. In Figure 60, the shape
of an ideal pulse is compared to an actual pulse.
An E1 pulse might need to conform to a standardized pulse
shape. This is often determined by comparing it to a specified
‘mask’. A commonly used pulse mask is defined by ITU-T G.703,
it is shown in the G.703 Mask illustration in Figure 60.
Note : For an E1 pulse with 120 W impedance, the signal level
is either ± 3 volts (for a binary 1 value) or 0 volts (for a binary 0
value) with real world values typically be ± 10%.
MTT-14B e_Manual D07-00-083P RevA00 Page 85 of 101