What is a PRBS Test?
PRBS stands for Pseudo-Random Binary Sequence. It’s a standard method used to evaluate the integrity and performance of transmission links by measuring bit errors.
Why is it used?
The PRBS test helps verify link stability and detect any issues that may cause data corruption. If the link introduces errors, it indicates potential problems with the fiber, transceiver, or configuration.
How does it work?
A sequence of pseudo-random bits is generated and transmitted from one end of the link. The receiver then compares the incoming bit stream against the expected pattern:
- If all bits match, the Bit Error Rate (BER) is zero, meaning the link is stable.
- If mismatches occur, bit errors are counted - signaling an unstable or degraded link.
How to perform the test:
You can perform a PRBS test using:
- External test instruments such as EXFO or Viavi.
- Network management systems (NMS) that support built-in PRBS functionality.
- Command-Line Interface (CLI) commands.
Example CLI command:
test interface et-0/1/3 prbs-test-start pattern-type <type> direction <0|1|2>
(Where direction defines transmit, receive, or both.)
After running the test, check the results using:
show interfaces
Types of PRBS Tests:
- Unidirectional: The bit stream is sent from one end and analyzed at the other.
- Bidirectional: The stream is sent from the local end and looped back from the remote side.
Both ends must have PRBS enabled for accurate results.
Applications:
PRBS testing is widely used to validate link quality, bit error performance, stability, and transceiver health - even on high-speed connections such as 100G, 200G, and beyond.
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