16
IDT82V2048 OCTAL T1/E1 SHORT HAUL LINE INTERFACE UNIT INDUSTRIAL TEMPERATURE RANGES
2.4.6.1 BPV DETECTION AND REPORTING IN AMI LINE CODING
AMI stands for Alternative Mark Inversion. It uses bipolar pulses to
represent logical values. A logic 0 is represented by no symbol and a
logic 1 by pulses of alternating polarity. In AMI line coding, marks
(pulses) are transmitted or received alternatively on tip and ring. If a
mark (pulse) is transmitted or received in the same polarity as the prior
mark (pulse), it is a bipolar violation.
Bipolar violation (BPV) is a non-zero signal element in an AMI signal
that has the same polarity as the previous non-zero signal element.
Figure-7 AMI Bipolar Violation
2.4.6.2
EXZ AND BPV DETECTION IN HDB3
The purpose of HDB3 is to prevent transmission of more than 3
consecutive zeros while maintaining DC balance. HDB3 encoder will
encode any 4 consecutive zeros as 000V or B00V where V is a bipolar
violation and B is a balancing pulse that is opposite in polarity to the
previous V. If there is an odd number of B pulses since the last V, then
the four consecutive zeros will be substituted as 000V. If there is an even
number of B pulses since the last V, then B00V substitution is chosen.
The HDB3 decoder, once receiving correctly encoded 000V or B00V, will
automatically restore the pattern back into 4 consecutive zeros.
HDB3 decoder will report an EXZ (excessive zero) when it receives 4
consecutive zeros.
The detection of code violation in 000V, coded for 4 consecutive
zeros in HDB3 line coding, depends on the number of alternate ones
between two consecutive ‘V’ (code violation) in the input data pattern. If
the number of alternate ones between two consecutive violations is an
odd number, no violation detection is reported. In Figure-8 input pattern,
there is one code violation detection for two 000V patterns. It can be
inferred that in Figure-8, there is another code violation prior to the first
000V pattern, and the number of alternate pulses between these two
violations is an odd number.
Conversely, if the number of alternate pulses between two violations
is an even number, there is a code violation reported for 000V as in
Figure-9.
Table-7 AIS Condition
ITU G.775 for E1
(Register LAC defaulted to ‘0’)
ETSI 300 233 for E1
(Register LAC set to ‘1’)
ANSI T1.231 for T1
AIS Detected
Less than 3 zeros contained in each of two
consecutive 512-bit stream are received
Less than 3 zeros contained in a 512-bit
stream are received
Less than 9 zeros contained in a 8192-bit stream (a ones
density of 99.9% over a period of 5.3 ms) are received
AIS Cleared
3 or more zeros contained in each of two
consecutive 512-bit stream are received
3 or more zeros contained in a 512-bit
stream are received
9 or more zeros contained in a 8192-bit stream are
received
Table-8 Error Detection
Hardware Mode Host Mode
Line Code Pin CVn Reports Line Code CODVn in e-CODV CZERn in e-CZER Pin CVn Reports
AMI Bipolar Violation AMI - - Bipolar Violation
B8ZS/
HDB3
Bipolar Violation +
Code Violation
B8ZS/HDB3
0 0 Bipolar Violation + Code Violation
0 1 Bipolar Violation + Code Violation + Excessive Zeros
1 0 Bipolar Violation
1 1 Bipolar Violation + Excessive Zeros
Bipolar Violation detectedBipolar Violation
RCLKn
RTIPn
RRINGn
RDn
CVn
1
2
3
4
5V
6
7
12 345 6V
