Full and half duplex transmissions

When studying telecommunications standards, it is important to understand the differences between half duplex and full duplex transmissions.

In a half duplex (HDX) transmission, a data packet is sent by one system and received by the other. Another data packet cannot be sent until the receiving system sends an acknowledgment back to the sender.

In a full duplex (FDX) transmission, both the sending and receiving systems communicate with each other simultaneously; in other words, both modems can send and receive data at the same time. This means a modem can be receiving a data packet while acknowledging the receipt of another.