The Receive Window size in a TCP segment is used to:
~ make sure that a sending application does not overflow the buffers in the sender's TCP implementation
~+ make sure that a sending application does not overflow the buffers in the receiver's TCP implementation
~ make sure that a sending application does not contribute to excessive network congestion
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If the Receive Window size is smaller than the bandwidth delay product for a TCP connection:
~+ The sender will not be able to use all of the available bandwidth for the connection
~ The sender may cause network congestion
~ The sender may overflow the receiver's buffers
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To achieve the simultaneous goals of preventing congestion and preventing receiver buffer overflow:
~ The sender must have at least as many unacknowledged bytes as the minimum of the receive window size and the sender's calculated congestion window size.
~+ The sender must have no more unacknowledged bytes than  as the minimum of the receive window size and the sender's calculated congestion window size.
~ The sender must have no more unacknowledged bytes than the maximum of the receive window size and the sender's calculated congestion window size.
~ The sender must have more unacknowledged bytes than as the maximum of the receive window size and the sender's calculated congestion window size.
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When a client initiates a TCP connection to a server, the 3-way handshake is initiated by:
~ the socket system call performed by the client
~ the accept system call
~ the bind system call
~+ the connect system call