Troubleshooting guide

E-2
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Appendix
Understanding show controllers Command Output
Understanding show controllers Command Output
The show controllers atm command displays any active alarms and non-zero error counters, referred to
in the output as facility statistics. Non-zero values indicate a problem with the physical wire between
this ATM switch router interface and another network device, typically an Add-Drop Multiplexer (ADM)
or an ATM switch.
Line Coding
Each binary one or zero on a digital link represents an electrical pulse. Digital systems alternate the
polarity of each successive binary one to ensure a sufficient amount of voltage transitions. Such alternate
mark inversion (AMI) is designed to ensure that the receiving device properly synchronizes and
determines when the binary ones and zeros arrive. Two consecutive pulses with the same polarity (both
positive or both negative) create a bipolar violation.
In addition to AMI, DS-3 links also support bipolar three zero substitution (B3ZS) and high-density
bipolar three (HDB3), respectively. These line coding methods area also used to maintain
synchronization by ensuring a sufficient number of binary ones.
Table E-1 explains Line coding errors displayed in the output of the show controllers atm command.
Note All parameters are accumulated in 15-minute intervals, and up to 96 intervals (24 hours worth) are
kept by the ATM switch router. Fewer than 96 intervals of data are available if the ATM switch router
has restarted within the last 24 hours. In addition, each performance parameter has a rolling 24-hour
total.
Table E-1 show controller Display Facilities Statistics and Explanations
Facility Statistic Explanation
Line Code Violation
(LCV)
Indicate the number of bipolar violation (BPV) or excessive zeros (EXZ)
errors. The conditions that cause this error to increment will vary with the
line coding.
Bipolar violation:
AMI—Receiving two successive pulses of the same polarity.
B3ZS or HDB3—Receiving two successive pulses of the same polarity, but
these pulses are not part of zero substitution.
Excessive zeros:
AMI—Receiving more than 15 contiguous zeros.
B3ZS—Receiving more than seven contiguous zeros.
Framing Bit Error (BE) Indicate the number of times that an incorrect pattern for the F1-to-F4
framing bits was detected.
Summed Excessive
Zeros (EZD)
Indicate the number of times that an “excessive” number of adjacent binary
zeros was detected. Excessive is defined as greater than three zeros for B3ZS
and greater than four zeros for HDB3.