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NE40E V800R010C00 Feature Description - WAN Access 01

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Basic Principles

Basic Principles

PRBS tests use the PRBS technique to generate a PRBS stream, encapsulate the PRBS stream into CES packets, send and receive the CES packets over CES service channels, and calculate the proportion of error bits to the total number of bits to obtain the BER of CES service channels for measuring service connectivity.

PRBS Stream

A PRBS stream is a pseudo random binary sequence of bits.

  1. PRBS stream generation: A PRBS stream is generated by a specific carry flip-flop using a multinomial. The multinomial varies according to the length of a sequence.
  2. PRBS stream measurement Figure 6-1 shows how PRBS stream measurement is implemented. After the PRBS module of PE1 generates a PRBS stream, the PRBS stream is encapsulated to CES packets, which are then sent by the network-side high-speed TX interface to PE2 over a PW. Upon receipt, PE2's line-side E1 interface performs a local loopback and sends the CES packets through the network-side interface to PE1's RX interface. After PE1 receives the packets, it compares the sent and received data and counts the error bits.

    Figure 6-1  PRBS stream measurement over a PW
  3. Bit error insertion during tests: During the tests, bit errors can be inserted to the PRBS stream. PE1 generates a PRBS stream and inserts bit errors. After the PRBS receive unit receives bit errors, PE1 can determine the test validity.
  4. Test termination by PRBS streams: If a PRBS test lasts for a long time, you can stop sending and receiving the PRBS stream to terminate the test.

PRBS tests are offline detections and interrupt services. Therefore, this function applies to site deployment and fault detection after a service interruption.

BER Calculation

The BER is calculated using the following equation:

BER = Number of error bits/(Interface rate x Test period)

Real-time and Historical Test Result Query

During the test, you can check the real-time test result to determine the real-time link quality. After the test ends, you can also check the historical test result to determine the historical link quality.

Updated: 2018-07-04

Document ID: EDOC1100027168

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