User guide

40 RealCT Direct API Developer Guide
Chapter 3: T1 Networking
Notice that in AMI line coding, each one alternates polarity and
the voltage returns to zero between pulses. Two subsequent
ones with the same polarity are called a bipolar violation.
Figure 7 shows a proper AMI signal and two bipolar violations.
Bipolar violations could lead to crackling on the line. To check
for bipolar violations, call RHT_GET_STATUS. See
Troubleshooting on page 81 for more information about how to
handle bipolar violations.
Figure 7. A Bipolar Violation in an AMI Signal
In AMI signaling, a long series of zeros is represented by a
constant 0V signal. The two ends can lose timing if there is no
signal on the line to synchronize them. To maintain ones
density on the line, some carriers replace zeros on the line with
ones. T1 devices support two line coding methods for
maintaining the appropriate ones density: ZCS and B8ZS.
In ZCS (Zero Count Substitution), the transmitting end replaces
the most significant bit of each eight-bit timeslot with a one,
regardless of whether the bit was a one or a zero. This method
is also called bit stuffing.
00110 0110
ar Violation