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For TCP to establish a connection between two systems the following must occur first:

1. Client sends a SYN connection from a random local port above 1024 to the destination Server Port which includes the Client's initial Sequence Number
2. If port is available the server responds with a new SYN to the source port of the Client. The Server sends a new random Sequence number and includes an Acknoledgement of the Client's originating Sequence number
3. The Client finalizes the three way handshake with an ACK that the request was received, with an Ack of the Servers Sequence number and a SEQ number of the Server's Acknoledgement which was originally based on the initial connection.