What is CRC checking? (SCI45409)

Answer

CRC was introduced at 4.3.00. CRC is Cyclical Redundancy Check. Each TCP buffer has CRC applied against the whole buffer and the number is placed in the TCP Header sent with each buffer sent over the connection. When the buffer is received - the CRC is calculated by the receiving side and matched against the CRC that the Sending side sent. A mismatch indicates network data corruption.As you know - Extended Compression will also detect network data corruption and pump out a message when the Network corrupts the data. The message issued is SCPA065I. However, with Extended Compression - the process will stop when the error is detected.The good thing about CRC is it will Detect when there is Network Data Corruption and instead of giving the SCPA065I message - which Stops the Process, CRC will Automatically Restart the Process from the Last Checkpoint Record. * A message will be issued when CRC finds an error so the customer will be aware that network data corruption was detected. The customer should check on the EC levels for their Routers to make sure they are not the source of the data corruption (this is usually - probably 99% of the time - the source of the data corruption. During heavy loads on the network - a router will corrupt the data. 
No, there is not much overhead with CRC - it's only a very few instructions that makes this calculation.The Administration Guide discusses CRC - specified in the Initialization Parameters and in the NETMAP.