The essence of ALE techniques is the use of automatic channel selection, scanning receivers, selective calling, handshaking, and robust burst modems. An ALE node decodes all received ALE signals heard on the channel(s) it monitors. It uses the fact that all ALE messages use forward error correction (FEC) redundancy. By noting how much error-correction occurred in each received and decoded message, an ALE node can detect the "quality" of the path between the sending station and itself. This information is coupled with the ALE address of the sending node and the channel the message was received on, and stored in the node's Link Quality Analysis (LQA) memory. When a call is initiated, the LQA lookup table is searched for matches involving the target ALE address and the best historic channel is used to call the target station. This reduces the likelihood that the call has to be repeated on alternate frequencies. Once the target station has heard the call and responded, a bell or other signalling device will notify both operators that a link has been established. At this point, the operators may coordinate further communication via orderwire text messages, voice, or other means. If further digital communication is desired, it may take place via external data modems or via optional modems built into the ALE terminal.