To conclude, here are the three most important points to remember about CRC in G.704 frames:

• CRC is an Error Detective: Its fundamental job is to detect if errors have occurred in a block of data during transmission. It does this by comparing a calculated “digital fingerprint” with one sent by the source.
• Context is Everything in G.704: The specific type of CRC used (e.g., CRC-4, CRC-6) and where its bits are located within the data stream depends entirely on the transmission speed (hierarchical level) and its corresponding frame structure as defined by the standard.
• Monitoring, Not Fixing: The ultimate goal of CRC in this context is to monitor the performance and health of a connection. It provides the essential data needed to know if a line is healthy or faulty, but it does not correct the data itself.