Troubleshooting guide

8-13
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 8 Troubleshooting the Cisco Catalyst 6509
Troubleshooting Serial Lines
Using Bit Error Rate Tests
This section discusses problem isolation using bit error rate (BER) tests. The topics discussed are:
• Configuring a BER Test on a T1 Line, page 8-13
• Sending a BER Test Pattern on a T1 Line, page 8-13
• Viewing the Results of a BER Test, page 8-14
• Terminating a BER test, page 8-16
Configuring a BER Test on a T1 Line
BER test circuitry is built into the CT3 line card. With BER tests, you can test cables and signal problems
in the field. You can configure individual T1 lines to run BER tests, but only one BER test circuit exists
for all 28 T1 lines. Hence, only one BER test can be run at once on a single T3 port.
The onboard BER test circuitry can generate two categories of test patterns: pseudorandom and
repetitive. Pseudorandom test patterns are exponential numbers and conform to CCITT/ITU O.151 and
O.153 specifications; repetitive test patterns are all zeros, all ones, or alternating zeros and ones.
Here is a description of each type of test pattern:
• Pseudorandom test patterns:
– 2^11 (per CCITT/ITU O.151)
– 2^15 (per CCITT/ITU O.151)
– 2^20 (per CCITT/ITU O.153)
– 2^20 QRSS (per CCITT/ITU O.151)
– 2^23 (per CCITT/ITU O.151)
• Repetitive test patterns:
– All zeros (0s)
– All ones (1s)
– Alternating zeros (0s) and ones (1s)
Both the total number of error bits received and the total number of bits received are available for
analysis. You can set the testing period from 1 minute to 14,400 minutes (240 hours), and you can also
retrieve error statistics anytime during the BER test.
When running a BER test, your router expects to receive the same pattern that it is transmitting. To help
ensure this:
• Use a loopback at a location of your choice in the link or network.
• Configure remote testing equipment to transmit the same BER test pattern at the same time.
Sending a BER Test Pattern on a T1 Line
You can send a BER test pattern on a T1 line with the controller command. The unframed option causes
the BER test pattern to use the entire T1 bandwidth, including the T1 framing as well as payload bits. If
unframed is omitted, then the T1 is either SF or ESF framed, as configured by the T1 framing command,
and the BER test pattern occupies only the T1 payload bits.