Transmission Control Protocol (TCP) TCP provides a connection-based, reliable byte-stream service to applications. Microsoft networking relies upon the TCP transport for logon, file and print sharing, replication of information between domain controllers, transfer of browse lists, and other common functions. It can only be used for one-to-one communications. TCP uses a checksum on both the headers and payload of each segment to reduce the chance that network corruption will go undetected. NDIS 5.0 provides support for task offloading, and Windows 2000 TCP takes advantage of this by allowing the NIC to perform the TCP checksum calculations if the NIC driver offers support for this function. Offloading the checksum calculations to hardware can result in performance improvements in very high-throughput environments. Windows 2000 TCP has also been hardened against a variety of attacks that were published over the past couple of years and has been subject to an internal security review intended to reduce susceptibility to future attacks. For instance, the initial sequence number algorithm has been modified so that ISNs increase in random increments, using an RC4-based random number generator initialized with a 2048-bit random key upon system startup.