Internet (IP) checksum
treat segment contents as sequence of 16-bit integers
checksum: addition (1’s complement sum) of segment contents
sender puts checksum value into UDP checksum field
compute checksum of received segment
check if computed checksum equals checksum field value:
- NO - error detected
- YES - no error detected. But maybe errors nonethless? More later ….
Goal: detect “errors” (e.g., flipped bits) in transmitted segment (note: used at transport layer only)