When Do Particular BIP Errors Occur?
Under some conditions, the output of the show controllers pos command reports only one level of BIP errors. The reason is that the reported BIP errors vary depending on where the code violation or bit flip actually occurs. In other words, parity bytes monitor and detect errors over different parts of a SONET frame. A BIP error can occur anywhere in the frame. This diagram illustrates a typical SONET network: When you connect two router POS interfaces point to point, over a dense wavelength division multiplexing (DWDM) link without intermediate SONET or Synchronous Digital Hierarchy (SDH) equipment, all three BIP mechanisms monitor the same segment, and typically detect the same errors. However, in this configuration, B2 must provide the most accurate bit error count. An increment in B1 and B2 errors, without an increment in B3 errors is statistically improbable. This condition occurs only if the errors affect parts of the frame that the B3 byte does not monitor. Recall that the B3 byte
