Figure 1710 example of three way handshakes 9

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Figure: 17.10 Example of Three-Way HandShakes 9. Describe the TCP Header Format. (20marks) Solution TCP uses only a single type of protocol data unit called a TCP segment. One header must serve to perform al protocol mechanisms with a minimum length of 20 octets. The fields are as follows: Source port (16 bits): source TCP user. Destination port (16 bits): destination TCP user. Sequence number (32 bits): sequence number of the first data octet in this segment except when SYN flag is set. If SYN is set, it is the initial sequence number (ISN) and the first data octet is ISN+1. Acknowledgment number (32 bits): a piggybacked acknowledgement. Contains the sequence number of the next data octet that TCP entity expects to receive. Data offset (4 bits): number of 32-bit words in the header. Reserved (6 bits): reserved for future use. Flags (6bits): URG : urgent pointer field significant ACK : acknowledgment field significant PSH : push function RST : reset the connection SYN : synchronize the sequence numbers FLN : no more data from sender Window (16bits): flow control credit allocation, in octets. Contains the number of data octets beginning with the one indicated in the acknowledgement field that the sender is willing to accept. Checksum (16 bits): the ones complements of the sum modulo 216 -1 of all the 16 –bit words in the segment plus a pseudo header. (Or)
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