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Interface Diagnostics

BERT allows you to troubleshoot problems by checking the quality of links. You can configure any of the following interfaces to execute a BERT when the interface receives a request to run this test: E1, E3, T1, T3; the channelized DS3, OC3, OC12, and STM1 interfaces; and the channelized DS3 IQ, E1 IQ, and OC12 IQ interfaces.

A BERT test requires a line loop to be in place on either the transmission devices or the far-end router. The local router generates a known bit pattern and sends it out the transmit path. The received pattern is then verified against the sent pattern. The higher the bit error rate of the received pattern, the worse the noise is on the physical circuit. As you move the position of the line loop increasingly downstream toward the far-end router, you can isolate the troubled portion of the link.

To configure BERT, you must configure the duration of the test, the bit pattern to send on the transmit path, and the error rate to monitor when the inbound pattern is received.

To configure the duration of the test, the pattern to send in the bit stream, and the error rate to include in the bit stream, include the bert-period, bert-algorithm, and bert-error-rate statements, respectively, at the [edit interfaces interface-name interface-type-options] hierarchy level:



[edit interfaces interface-name interface-type-options]

bert-algorithm algorithm;

bert-error-rate rate;

bert-period seconds;

By default, the BERT period is 10 seconds. You can configure the BERT period to last from 1 through 239 seconds on some PICs and from 1 through 240 seconds on other PICs.

rate is the bit error rate. This can be an integer from 0 through 7, which corresponds to a bit error rate from 10^–0 (1 error per bit) to 10^–7 (1 error per 10 million bits).

algorithm is the pattern to send in the bit stream. For a list of supported algorithms, enter a ? after the bert-algorithm statement; for example:

[edit interfaces t1-0/0/0 t1-options]

user@host# set bert-algorithm ?

Possible completions:
  pseudo-2e11-o152     Pattern is 2^11 -1 (per O.152 standard)
  pseudo-2e15-o151     Pattern is 2^15 - 1 (per O.152 standard)
  pseudo-2e20-o151     Pattern is 2^20 - 1 (per O.151 standard)
  pseudo-2e20-o153     Pattern is 2^20 - 1 (per O.153 standard)
        ...

For specific hierarchy information, see the individual interface types.

Note: The 4-port E1 PIC supports only the following algorithms:

pseudo-2e11-o152     Pattern is 2^11 -1 (per O.152 standard)
pseudo-2e15-o151     Pattern is 2^15 - 1 (per O.151 standard)
pseudo-2e20-o151     Pattern is 2^20 - 1 (per O.151 standard)
pseudo-2e23-o151     Pattern is 2^23 (per O.151 standard)

When you issue the help command from the CLI, all BERT algorithm options are displayed, regardless of the PIC type, and no commit check is available. Unsupported patterns for a PIC type can be viewed in system log messages.

Table 24 shows the BERT capabilities for various interface types.

Table 24: BERT Capabilities by Interface Type

Interface	T1 BERT	T3 BERT	Comments
E1 or T1	Yes (port 0–3)	Yes (port 0–3)	Single port at a time Limited algorithms
E3 or T3	Yes (port 0–3)	Yes (port 0–3)	Single port at a time
Channelized OC12	N/A	Yes (channel 0–11)	Single channel at a time Limited algorithms No bit count
Channelized STM1	Yes (channel 0–62)	N/A	Multiple channels Only one algorithm No error insert No bit count
Channelized T3 and Multichannel T3	Yes (channel 0–27)	Yes (port 0–3 on channel 0)	Multiple ports and channels Limited algorithms for T1 No error insert for T1 No bit count for T1

These limitations do not apply to channelized IQ interfaces. For information about BERT capabilities on channelized IQ interfaces, see Channelized IQ and IQE Interfaces Properties.

Starting and Stopping a BERT Test

Before you can start the BERT test, you must disable the interface. To do this, include the disable statement at the [edit interfaces interface-name] hierarchy level:



[edit interfaces interface-name]

disable;

After you configure the BERT properties and commit the configuration, begin the test by issuing the test interface interface-name interface-type-bert-start operational mode command:



user@host> test interface interface-name interface-type-bert-start

The test runs for the duration you specify with the bert-period statement. If you wish to terminate the test sooner, issue the test interface interface-name interface-type-bert-stop command:



user@host> test interface interface-name interface-type-bert-stop

For example:



user@host> test interface t3-1/2/0 t3-bert-start

user@host> test interface t3-1/2/0 t3-bert-stop

To view the results of the BERT test, issue the show interfaces extensive | find BERT command:



user@host> show interfaces interface-name extensive | find BERT

For more information about running and evaluating the results of the BERT procedure, see the JUNOS System Basics and Services Command Reference.

Note: To exchange BERT patterns between a local routing platform and a remote routing platform, include the loopback remote statement in the interface configuration at the remote end of the link. From the local routing platform, issue the test interface command.

Example: Configuring Bit Error Rate Testing

Configure a BERT test on a T3 interface. In this example, the run duration lasts for 120 seconds. The configured error rate is 0, which corresponds to a bit error rate of 10^–0 (1 error per bit). The configured bit pattern of all-ones-repeating means that every bit the interface sends is a set to a value of 1.



[edit interfaces]
t3-1/2/0 {


t3-options {
bert algorithm all-ones-repeating;
bert-error-rate 0;
bert-period 120;
}


}

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