Optics and Hardware Configuration Guide for Cisco 8000 Series Routers

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Pseudo random binary sequences

Updated: June 16, 2026

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Introduces pseudo random binary sequences and explains the core idea and technical context. Highlights the main characteristics and usage guidance needed before configuration.

The Pseudo Random Binary Sequence (PRBS) feature provides a robust mechanism for performing data integrity checks on router interfaces by generating and analyzing pseudo-random bit patterns. It operates simultaneously on both the transmit (Tx) and receive (Rx) directions without generating actual client traffic, ensuring that the optical links and interfaces maintain a good state and are error-free.

Feature Name Release Information Feature Description
PRBS support for high-speed optical interfaces Release 25.4.1

Introduced in this release on: Modular Systems (8800 [ASIC: Q200])

The Pseudo Random Binary Sequence (PRBS) feature provides data integrity checks on router interfaces by generating and analyzing pseudo-random bit patterns, PRBS15 and PRBS31 between the Cisco 88-LC0-36FH router line card and QDD-400G-FR4 optics.

CLI:

This feature introduces these commands:

  • controller Optics R/S/I/P prbs-mode <source/sink/source-sink> pattern <pn15/pn31> direction <line/system>

  • show controllers optics R/S/I/P prbs-details

The feature supports PRBS15 and PRBS31 patterns, which correspond to pseudo-random sequences of lengths 2^15-1 and 2^31-1 bits respectively.

PRBS is typically employed during system installations, or when replacing line cards or nodes, especially in Ethernet-based lossless fabric environments such as simple two-tier leaf and spine network designs.

PRBS operational modes

PRBS testing uses three primary operational modes to check data integrity on links without generating live client traffic

You can configure PRBS in one of the modes on the optics controller.

  • Source mode — The device continuously generates the PRBS signal on the line according to the configured pattern.

  • Sink mode — The device locks onto the incoming PRBS signal, analyzes it, and reports any errors detected.

  • Source-Sink mode — The device acts as both transmitter and receiver, generating the PRBS pattern and simultaneously verifying the incoming signal for errors.

Limitations for PRBS on optics controllers

  • The PRBS support is limited to modules that comply with the QSFP-DD Common Management Interface Specification (CMIS).

  • User-defined pattern is not supported.

  • Configuration is supported only on the main controller and is not supported on breakout controllers.