Here we see a count of CRC errors
on an automotive CAN communication link.
Signal integrity problems usually show up at the protocol level as disparity errors, coding errors, or CRC errors. Before jumping into the cause of bit-level errors it is important to understand that 10-bit characters are transmitted to represent each 8-bit byte, and disparity describes the ratio of 1's to 0's in each 10-bit character.
CRC Errors occur when the 32-bit CRC value at the end of each frame is incorrect.
To effectively assess the bit-error rate of the air interface, power management or call signaling of the mobile subscriber, WAP testing requires analysis of CRC errors
of the protocol data units (PDUs), TCP datagram time-outs and the WAP protocols.
The initiator will then read back and compare the data and check for parity and CRC errors
. If the test fails, the initiator will repeat the test at the next lower speed, until a compatible speed is detected.
The switches route and monitor individual cells, but without decoding, AAL5 cannot analyze length or CRC errors.
In the following example, the router experiences a high number of CRC errors, while the Internet Service Provider (ISP) receives a multitude of complaints from customers experiencing poor Web access.
In this example, the test device reports a constant rate of AAL5 CRC errors, but no length errors, on all channels.
For example, a network administrator tracking down an intermittent fault could have ProbeView furnish an alert whenever CRC errors
exceeded a certain limit.