ISN (Initial Sequence Number)

RU: ISN (начальный номер последовательности)

Initial Sequence Number: the 32-bit value a TCP endpoint picks for its first byte when opening a connection, exchanged in the SYN segment. RFC 6528 requires ISNs to be generated with a cryptographic hash of the connection tuple and a secret, so an off-path attacker cannot predict the ISN and inject or hijack the stream.