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30-2
Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 30 Bit Error Rate Testing
Feature Overview
• To determine if the remote serial port returns the BERT pattern unchanged, you must manually
enable network loopback at the remote serial port while you configure a BERT pattern to use in the
test at specified time intervals on the local serial port.
Restrictions
• BERT affects the functionality of any configured protocol on a controller on which it is initiated.
The configured protocol functionality is resumed after the BERT process is completed or
successfully aborted.
• BERT is not supported for channelized E1/T1 (per timeslot).
Feature Overview
The BERT feature is used to test the integrity of the physical layer. Using this feature, you can test cables
and diagnose signal problems in the field.
BERT generates a specific pattern on to the egress data stream of a E1/T1 controller and then analyzes
the ingress data stream for the same pattern. The bits that do not match the expected pattern are counted
as bit errors.
The bit error rate (BER) is determined by comparing the erroneous bits received with the total number
of bits received. You can display and analyze the total number of error bits transmitted and the total
number of bits received on the link. You can retrieve error statistics anytime during the BERT.
The ASR 901 router uses Pseudo-Random Binary Sequences (PRBSs) for the BERT. The following table
lists the PRBSs supported on the ASR 901 routers.
Table 30-1 BERT Pattern Supported in Cisco ASR 901 Routers
How to Configure BERT
The ASR 901 router supports BERT on all 16 E1/T1 controllers simultaneously. Additionally, you can
abort an already initiated BERT.
This section describes how to configure and perform a BERT on E1/T1 controllers, and how to stop or
verify the test:
• Performing BERT on a T1/E1 Line, page 30-3 (Required)
BERT Pattern Description
0’s Test pattern consisting of all 0’s that is used to test line coding
1’s Test pattern consisting of all 1’s that is used to test alternating line volt and
repeaters
2^11 Pseudo-random repeating test pattern that consists of 2,048 bits
2^15 Pseudo-random repeating test pattern that consists of 32,767 bits
2^20 QRSS Pseudo-random repeating test pattern that consists of 1,048,575 bits
Alt 0’s and 1’s Test pattern consisting of alternating 0’s and 1’s that is used to test the
preamp and equalizer