basic-message-flow.msc

msc {
    arcgradient=10;

    a [label="Client"], b [label="Server"];

    a=>>b [label="startup packet\n\n"];

    a<<=b [label="auth request | auth OK\n\n"];

    a=>>b [label="(optional) PasswordMessage\n\n"];

    |||;

    b=>>a [label="ParameterStatus\n\n"];
    b=>>a [label="ParameterStatus\n\n"];
    b=>>a [label="ParameterStatus\n\n"];

    b=>>a [label="BackendKeyData\n\n"];

    b=>>a [label="ReadyForQuery\n\n"];
}