The SOURCE PORT is assigned by your machine and the DESTINATION PORT by the remote machine. The header contains a SEQUENCE NUMBER that is used by the destination machine to build the message and to see if any datagrams are missing. The CHECKSUM is a number that is computed by adding up all of the octets in the datagram, and the result is put in the header. Once the computer at the remote end receives the datagram and verifies the checksum, it places an Acknowledgment number in the header and sends it back to the source computer. So, now is when TCP hands it off to IP. The amount of datagrams depends on the file size. Details of IP The main brake lining manufacturers things in this header are the SOURCE and DESTINATION address, and they are the same as the TCP header. The PROTOCOL tells IP which protocol to deliver it to, either TCP or one of the other protocols brake pad suppliers that use IP. The CHECKSUM in the IP header is verified at the other computer to make sure the datagram was not damaged in transit. The time to live field is how long the packet will live before it's erased. The reason for this is not to have stranded packets clogging up the network. For File transfers, mail sending and retrieval, and remote logins TCP/IP is the protocol of choice. It has the minimum lose of data, while insuring pinpoint delivery. TCP/IP is invisible to the user; therefore, the user doesn't have to worry about configuring TCP/IP.