Introduction to Data Communications
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3. Back at the Transmit End:

a. Modem sends CD(Tx) - We're connected and they are sending us good carrier!
b. PC sends RTS(Tx) - Okay send them our carrier (1170 Hz).
c. Modem waits - Delay so that Rx modem can lock to the carrier
d. Modem sets CTS(Tx) - Okay now we should be ready to send data
e. PC sends TxD(Tx) - Here's some data to send over.

4. At the Receive End:

a. Modem sends CD(Rx) - We're connected & they're sending good carrier (1170 Hz
b. Modem sends Rxd(Rx) - Here's some data for you.

The communication program then interprets the data and decides if a reply is required or if more data is coming. The communication programs handle the transfer of the data and the direction.

5. Both Originate or Answer can end the communication:

a. DTE(Tx) drops RTS(Tx) or DTR(Tx) - I'm done, hang-up the phone.
b. DCE(Tx) modem drops DSR(Tx) and the Carrier (1170 Hz) - I've disconnected.
c. DCE(Rx) modem drops CD(Rx) - No carrier, they're hanging up
d. DTE(Rx) drops RTS(Rx) - Hang up on them
e. DCE(Rx) modem drops DSR(Rx) and the Carrier (2125 Hz) - I've disconnected.

Introduction to Data Communications
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